Python: Flow Control Statements

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Python: Flow Control Statements

Flow control statements

Flow control statements in Python determine the order in which your code is executed. They allow you to make decisions, repeat actions, and control the program’s flow based on specific conditions.

Conditional Statements (if, else, elif)
Looping Statements (for, while)
Loop Control Statements (break, continue, pass)
Match Statement (Python 3.10+)

Conditional Statements (if, else, elif)

The if statement in Python is a conditional statement that allows you to execute a block of code only if a certain condition is met.
Make decisions using if, elif, and else statements.

The general syntax of the if statement is as follows:

if condition:
    # code to execute if condition is True

The condition can be any logical expression. If the condition is evaluated to true, the block of statements is executed. Otherwise, the block of statements is skipped.

Here is a simple example of an if statement in MATLAB:

Example #1:

x = 10

if x > 5:
    print('x is greater than 5.')

This code will print the message x is greater than 5. to the console.

You can also use elif statements to check for multiple conditions. The general syntax of the elif statement is as follows:

if condition1:
    # code to execute if condition1 is True
elif condition2:
    # code to execute if condition2 is True

If the condition for the if statement is evaluated to false, the python interpreter will check the condition for the first elif statement. If the condition for the elif statement is evaluated to true, the corresponding block of statements is executed. Otherwise, the python interpreter will check the condition for the next elif statement, and so on.

Here is an example of an if statement with an elif statement:

x = 3

if x > 5:
    print('x is greater than 5.')
elif x < 5:
    print('x is less than 5.')

This code will print the message “x is less than 5.” to the console.

You can also use an else statement to check for all other conditions. The general syntax of the else statement is as follows:

if condition1:
    # code to execute if condition1 is True
elif condition2:
    # code to execute if condition2 is True
else:
    # code to execute if none of the conditions are True

If all of the conditions for the if and elseif statements are evaluated to false, the block of statements in the else statement is executed.

Here is an example of an if statement with an elif statement and an else statement:

x = 2

if x > 5:
    print('x is greater than 5.')
elif x == 5:
    print('x is equal to 5.')
else:
    print('x is less than 5.')

Output: This code will print the message “x is less than 5.” to the console.

Example #2: Basic If-Else

number = 10

if number > 0:
    print("The number is positive")
else:
    print("The number is not positive")

Explanation: This code checks if the variable number is greater than 0. If true, it prints “The number is positive”, otherwise it prints “The number is not positive”.

Example #3: Checking Even or Odd

Example #4: Age Group Classification

age = 25

if age < 18:
    print("Minor")
else:
    print("Adult")

Explanation: This code classifies a person as a “Minor” if their age is less than 18, and as an “Adult” otherwise.

Example #5: Grade Assignment

realted video

score = 85

if score >= 90:
    print("Grade: A")
elif score >= 80:
    print("Grade: B")
elif score >= 70:
    print("Grade: C")
else:
    print("Grade: F")

Explanation: This code assigns a grade based on the score. It uses multiple elif statements to check for different score ranges.

Example #6: Nested If-Else

number = -5

if number >= 0:
    if number == 0:
        print("The number is zero")
    else:
        print("The number is positive")
else:
    print("The number is negative")

Explanation: This code uses nested if-else statements to check if the number is zero, positive, or negative.

Example #7: Temperature Check

temperature = 30

if temperature > 30:
    print("It's a hot day")
else:
    print("It's not a hot day")

Explanation: This code checks if the temperature is greater than 30. If true, it prints “It’s a hot day”; otherwise, it prints “It’s not a hot day”.

Example #8: Voting Eligibility [video]

age = 17

if age >= 18:
    print("You are eligible to vote")
else:
    print("You are not eligible to vote")

Explanation: This code checks if a person is eligible to vote based on their age. If age is 18 or more, it prints “You are eligible to vote”; otherwise, it prints “You are not eligible to vote”.

Example #9: Checking String Length

string = "Hello, World!"

if len(string) > 10:
    print("The string is long")
else:
    print("The string is short")

Explanation: This code checks if the length of the string is greater than 10. If true, it prints “The string is long”; otherwise, it prints “The string is short”.

Task #1: Password Check

Objective: Write a Python program that checks if the provided password matches the correct password and prints an appropriate message.

Instructions:

Define a variable password and set it to a string value.
Create an if-else condition to compare the password with the correct password "password123".
If the password matches "password123", print "Access granted".
If the password does not match, print "Access denied".

Example Input/Output:

Input 1:

password = "password123"

Output 1:

Access granted

Input 2:

password = "wrongpassword"

Output 2:

Access denied

Explanation:

The program compares the variable password with the correct password "password123".
In Example 1, since the password is correct, the output is "Access granted".
In Example 2, since the password is incorrect, the output is "Access denied".

Task #2: Compare Two Numbers in Python

Write a Python program that compares two numbers a and b. If a is greater than b, the program should print the message “a is greater than b”. Otherwise, it should print “a is not greater than b”.

Input:

The program sets two variables a and b to specific values (15 and 20 in this case).
The comparison is then made based on these values.

Expected Output:

The program will print one of the following outputs depending on the values of a and b:
1. If a is greater than b:
  Output:
  "a is greater than b"
2. If a is less than or equal to b:
  Output:
  "a is not greater than b"

Example:

Input:
a = 15, b = 20

Output:
"a is not greater than b"
Input:
a = 25, b = 20

Output:
"a is greater than b"

Explanation: This code checks the relationship between a and b. If a is greater than b, it prints a message saying so; otherwise, it prints a different message.

Task #3: Determine if a Number is Negative, Zero, or Positive

Write a Python program that checks whether a number x is negative, zero, or positive. The program should print:

“Negative” if x is less than 0,
“Zero” if x is equal to 0, and
“Positive” if x is greater than 0.

Input:

The program sets a variable x to a specific value (10 in this case).

Expected Output:

The program will print one of the following outputs based on the value of x:
1. If x is less than 0:
  Output:
  "Negative"
2. If x is equal to 0:
  Output:
  "Zero"
3. If x is greater than 0:
  Output:
  "Positive"

Example:

Input:
x = 10

Output:
"Positive"
Input:
x = -5

Output:
"Negative"
Input:
x = 0

Output:
"Zero"

Explanation: This code checks whether the value of x is less than 0, equal to 0, or greater than 0, and prints the corresponding message based on the comparison.

Task #4: Compare Two Input Numbers

Write a program that takes two numbers as input and prints whether the first number is greater than, less than, or equal to the second number.

Input:

Enter the first number: 10
Enter the second number: 5

Sample Output:

10 is greater than 5

Another Sample Input:

Enter the first number: 4
Enter the second number: 4

Output:

4 is equal to 4

Task #5: Age Checker

Write a simple program that asks for the user’s age and checks if the user is older than 18.

Sample Input:

Enter your age: 20

Sample Output:

You are older than 18.

Another Sample Input:

Enter your age: 16

Output:

You are younger than 18.

Task #6: Divisibility Check

Write a program that checks if a given number is divisible by both 2 and 3.

Input:

A single integer, n.

Output:

Print “Yes” if the number is divisible by both 2 and 3.
Print “No” otherwise.

Example:

Input:
6
Output:
Yes
Input:
10
Output:
No

Task #7: Voting Eligibility Check

Create a program that takes the age and country of a person as input and checks if they are eligible to vote in that country (consider the voting age as 18 and the country as “USA”).

Input:

An integer age, representing the person’s age.
A string country, representing the person’s country.

Output:

Print “Eligible to vote” if the person is 18 years or older and from the USA.
Print “Not eligible to vote” otherwise.

Example:

Input:
age = 20
country = USA
Output:
Eligible to vote
Input:
age = 17
country = USA
Output:
Not eligible to vote
Input:
age = 25
country = Canada
Output:
Not eligible to vote

loops

There are two ways to create loops in Python: with the for-loop and the while-loop.
Repeat actions using for and while loops.

for loop

A for loop in Python is a programming statement that repeats a block of code a fixed number of times.
The for-loop is always used in combination with an iterable object¹, like a list or a range.
The Python for statement iterates over the members of a sequence in order, executing the block each time.

video: What is it and Why do we Use it? | Python For loop Tutorial

Syntax:

for item in iterable:
    # code block

iterable is a sequence of elements such as a list, tuple, dictionary, set, or string. item is a variable that takes on the value of each element in the sequence, one at a time. The code block is executed once for each element in the sequence.

range() function:

We can use the range() function as an iterable in a for loop in Python. The range() function returns a sequence of numbers, starting from 0 by default, and increments by 1 (by default), and ends at a specified number.
We can also specify the starting value and the increment value of the sequence using the range() function. For example, range(2, 10, 2) returns a sequence of numbers starting from 2, incrementing by 2, and ending at 8. read more …

Here are the common usages:

Single Argument (stop):
```
range(stop)
```
- Generates numbers from 0 up to, but not including, stop.
```
range(5)  # Output: 0, 1, 2, 3, 4
```
Two Arguments (start, stop):
```
range(start, stop)
```
- Generates numbers from start up to, but not including, stop.
```
range(2, 5)  # Output: 2, 3, 4
```
Three Arguments (start, stop, step):
```
range(start, stop, step)
```
- Generates numbers from start up to, but not including, stop, incrementing by step. The step can be positive or negative.
```
range(1, 10, 2)  # Output: 1, 3, 5, 7, 9
range(10, 1, -2) # Output: 10, 8, 6, 4, 2
```

Note: range() produces an immutable sequence type, which is often used in loops. To get a list of numbers, you can convert the range object to a list:

list(range(5))  # Output: [0, 1, 2, 3, 4]

Example #9: Print Numbers from 1 to 5

video

Question: Write a Python program to print the numbers from 1 to 5, using a for loop.

for i in range(6):
    print(i)

Example #10: Printing “Building the future, one line at a time.” 5 Times Using a for Loop

Question: Write a Python program to print the string “Building the future, one line at a time.” 5 times, using a for loop.

for i in range(5):
    print("Building the future, one line at a time.")

Example #11: Sum of Numbers from 1 to N

Question: Write a python program to calculate the sum of the first N natural numbers using a for loop.

video: Calculate the sum of the first N natural numbers | Python for loop example

Task #8: Sum of Numbers in a Range

Description:

Write a Python program that asks the user to input two numbers, a start and an end value, and calculates the sum of all the numbers in that range (inclusive) using a for loop.

Input:

The program should prompt the user to enter two integers:
1. The start of the range.
2. The end of the range.

Output:

The program should display the sum of all the numbers in the given range.

Example:

Input:

Enter the start of the range: 1
Enter the end of the range: 5

Output:

The sum of numbers from 1 to 5 is: 15

Requirements:

Use a for loop to iterate through the range.
Accumulate the sum of numbers using a variable inside the loop.

Task #9: Display Even Numbers in a Range

Description:

Write a Python program that asks the user to input two numbers, a start and an end value, and displays all the even numbers between the two values (inclusive) using a for loop.

Input:

The program should prompt the user to enter two integers:
1. The start of the range.
2. The end of the range.

Output:

The program should display all the even numbers in the range in ascending order, one number per line.

Example:

Input:

Enter the start of the range: 2
Enter the end of the range: 10

Output:

Requirements:

Use a for loop to iterate through the range.
Check if a number is even using the modulus (%) operator.

Example #12: Print Even Numbers from 2 to 10 and sum of even numbers

Question: Write a Python program to display the even numbers from 2 to 10 and sum of even numbers, inclusive, using a for loop.

sum = 0
for i in range(2,11):
    if i%2 == 0:
        sum +=i
        print(i)
print(f"Sum of even numbers: {sum}")

Task #10: Display Multiplication Tables**

Description:

Write a Python program that asks the user to input a number and displays its multiplication table up to 10 using a for loop.

Input:

The program should prompt the user to enter an integer value.

Output:

The program should display the multiplication table for the entered number in the following format:

n x 1 = n
n x 2 = 2n
...
n x 10 = 10n

Example:

Input:

Enter a number: 5

Output:

x 1 = 5
x 2 = 10
x 3 = 15
x 4 = 20
x 5 = 25
x 6 = 30
x 7 = 35
x 8 = 40
x 9 = 45
x 10 = 50

Requirements:

Use a for loop to generate and display the multiplication table.

Example #13: String as an iterable

video: String as an iterable

Example #14: Lists as an iterable

collection = ['python', 5, 'd']
for x in collection:
    print(x)

Example #15: Loop over Lists of lists

list_of_lists = [ [1, 2, 3], [4, 5, 6], [7, 8, 9]]
for list in list_of_lists:
    for x in list:
        print(x)

A nested loop is a loop inside another loop. It is a powerful programming technique that can be used to solve a wide variety of problems.

Example #16 Nested Loops - Multiplication Tables

for i in range(1, 11):
    print(f"Multiplication table of {i}")
    for j in range(1, 11):
        print('%d * %d = %d' % (i, j, i*j))

Why We Use Variables in For Loops

In Python, a variable in a for loop is used to iterate over a sequence (like a list, tuple, string, or range) and access each element in that sequence one at a time. This variable is often called the “loop variable” or “iterator variable.”

Understanding the Role of the Variable:

Accessing Elements: The loop variable allows you to access each element in the sequence during each iteration of the loop. This makes it possible to perform operations on each element.
Dynamic Assignment: The loop variable automatically takes the value of the next element in the sequence during each iteration. This saves you from having to manually update the variable’s value.
Readability and Simplicity: Using a loop variable makes the code more readable and easier to understand. You can name the variable in a way that reflects the data it represents, making the code more self-explanatory.
Control Over Iteration: The loop variable gives you control over the loop’s execution. You can use it to control the flow, such as skipping certain elements, breaking out of the loop early, or performing specific actions based on the variable’s value.

Example #17: Loop Through a List of Fruits in Python

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

In this example, the loop variable fruit takes on the value of each element in the list fruits during each iteration. The output will be:

apple
banana
cherry

The variable fruit is used to access and print each element in the fruits list.

Use of underscore in ‘For Loop’

In Python, an underscore (_) is often used as a variable name in a for loop (or any other context) when the value of the variable is not needed.
This is a common convention to indicate that the value is intentionally being ignored or discarded.

For example, if you want to repeat an action a certain number of times but don’t need to use the loop variable, you can use _:

Example #18: Using an Underscore in a Loop to Print “Hello” Multiple Times

for _ in range(5):
    print("Hello")

Here, _ is used instead of a variable name like i or j because the value is not important. The loop will simply print “Hello” five times without using the loop index. This helps to make the code more readable by signaling to other programmers that the loop variable is not used in the loop’s body.

video: Underscore to Ignore Values in for loop

while loop

A while loop in python is a control flow statement that repeatedly executes a block of code until a specified condition is met.

Syntax:

while condition:
    # code block

Here, condition is a boolean expression that is evaluated before each iteration of the loop. If the condition is True, the code block is executed. The loop continues to execute as long as the condition remains True.

video: Python while loop example - Learn how to use while loop

Example #19: Print numbers from 1 to 10 using while loop

Question: Write a Python program to print the numbers from 1 to 10, using a while loop?

count = 1  # Start counting at 1
while count <= 10:  # Keep counting as long as we're less than or equal to 10
    print(count)  # Print the current number
    count += 1  # Add 1 to the count for the next round

Example #20: Print “Hello, world!” 5 times using while loop

Question: Write a Python program to print the string “Hello, world!” 5 times, using a while loop?

i = 1
while i <= 10:
    print('Hello, world!')
    i += 1

Task #10: Display Multiplication Tables**

Description:

Write a Python program that asks the user to input a number and displays its multiplication table up to 10 using a while loop.

Input:

The program should prompt the user to enter an integer value.

Output:

The program should display the multiplication table for the entered number in the following format:

n x 1 = n
n x 2 = 2n
...
n x 10 = 10n

Example:

Input:

Enter a number: 5

Output:

x 1 = 5
x 2 = 10
x 3 = 15
x 4 = 20
x 5 = 25
x 6 = 30
x 7 = 35
x 8 = 40
x 9 = 45
x 10 = 50

Requirements:

Use a while loop to generate and display the multiplication table.

Task #11: Sum Integers from 1 to 100 Using While Loop

Write a Python program that calculates the sum of all integers from 1 to 100. The program should use a while loop to iterate through these integers and accumulate their sum.

Input:

The program initializes a variable i to 1 and a variable sum to 0.
The loop continues while i is less than or equal to 100.

Expected Output:

The program will print the total sum of integers from 1 to 100 in the following format:
Sum = {sum}

Example Output:

Sum = 5050

Explanation: This code uses a while loop to iterate through the integers from 1 to 100. In each iteration, the current value of i is added to the variable sum, and i is incremented by 1. After the loop completes, the total sum is printed.

Example #21: Sum of even numbers from 2 to 20 using while loop

Question: Write a Python program to calculate the sum of the even numbers from 2 to 20 using a while loop.

sum = 0  # Initialize a variable to store the sum
number = 1  

while number <= 20:
    if number%2 == 0:
      sum += number  # Add the current number to the sum
    number += 1

print(f'The sum of even numbers from 1 to 20 is: {sum}')

Task #12: Calculate Squares of Numbers from 1 to 4 Using While Loop

Write a Python program that calculates and prints the square of the numbers from 1 to 4. The program should use a while loop to iterate through these numbers.

Input:

The program initializes a variable i to 1 and continues looping while i is less than 5.

Expected Output:

The program will print the square of each number from 1 to 4 in the following format:
Square of {i} is {square}

Example Output:

Square of 1 is 1
Square of 2 is 4
Square of 3 is 9
Square of 4 is 16

Explanation: This code uses a while loop to calculate the square of the variable i, which starts at 1 and increments by 1 in each iteration until it reaches 5. The squares of the numbers 1 through 4 are printed during each iteration.

Example #22: Prompt User for Input Until Blank Line is Entered

Question: Write a Python program to prompt the user to enter lines of text until the user enters a blank line. The program should then display the message “You entered a blank line.”.

inputStr = 'Start'

while inputStr != "":
  inputStr = input("Enter a line of text:")

print('You entered a blank line.')

Example #23: Sum User-Entered Numbers Until Zero is Entered

Question: Write a Python program to add all the numbers entered by the user until the user enters zero. The program should display the sum of the numbers.

sum = 0; # Initialize the sum

# Prompt the user to enter a number
number = int(input('Enter a number: ')) # int() Convert string input to integer

# While the number entered is not zero, add the number to the sum and prompt the user to enter another number
while number != 0:
    sum += number
    number = int(input('Enter another number: ')) # int() Convert string input to integer
    
# Display the sum of the numbers
print(f'The sum of the numbers is: {sum}')

Task #13: Sum User-Entered Numbers Until a Negative Number is Entered

Write a Python program that prompts the user to enter numbers. The program should keep accepting numbers until the user enters a negative number. Once a negative number is entered, the program should stop and display the sum of all the numbers entered (excluding the negative number).

Sample Input:

Enter a number (negative number to stop): 10
Enter another number (negative number to stop): 20
Enter another number (negative number to stop): 5
Enter another number (negative number to stop): -1

Sample Output:

The sum of all numbers is: 35

Task #14: Number Guessing Game

Instructions:

Write a Python program where the computer picks a random number between 1 and 10, and the user has to guess it.
The program should continue asking the user for a guess until they guess the correct number.
After each incorrect guess, the program should give a hint whether the guess is too low or too high.

Example Code:

import random

# Step 1: Computer picks a random number between 1 and 10
secret_number = random.randint(1, 10)

# Step 2: Initialize the guess variable to None
guess = None

# Step 3: Use a while loop to keep asking the user for input

# write your code here

Sample Input and Output:

Guess a number between 1 and 10: 4
Too low! Try again.
Guess a number between 1 and 10: 9
Too high! Try again.
Guess a number between 1 and 10: 7
Too low! Try again.
Guess a number between 1 and 10: 8
Congratulations! You guessed the correct number.

This sample demonstrates:

How the user is prompted repeatedly.
Feedback on whether their guess is too low or too high.
A congratulatory message when the correct guess is made.
Example #24: Infinite Loop Printing Messages with Counter

Video: Learn how to use INFINITE while loop)

x = 1
while True:
    print("To infinity and beyond! We're getting close, on %d now!" % (x))
    x += 1

while loop examples:

See also:

[video: Python Loops Performance Comparison: For vs. While

Which is Faster?](https://youtu.be/6JNeo6TVQN8)

Loop Control Statements (break, continue, pass)

These statements modify the behavior of loops.

break: Terminates the loop entirely. continue: Skips the current iteration and moves to the next one. pass: Does nothing, often used as a placeholder.

`break`

Exits the loop prematurely.

for item in sequence:
    if some_condition:
        break  # exit the loop

`continue`

Skips the current iteration and proceeds to the next iteration of the loop.

for item in sequence:
    if some_condition:
        continue  # skip the rest of the code in this iteration
    # code to execute if some_condition is False

`pass`

A null statement, used as a placeholder.

if condition:
    pass  # do nothing

Example #: Using Break Statement in a Loop with Range

for x in range(3):
    if x == 1:
        break

Example #: Print Odd Numbers Less Than 5 with Loop Control Statements (break, continue)

for i in range(10):
    if i == 5:
        break  # exit the loop when i is 5
    if i % 2 == 0:
        continue  # skip even numbers
    print(i)  # print only odd numbers less than 5

The else Clauses on Loops

In Python, the else clause can be used with loops (for and while). This may be surprising at first since most people associate else with if statements. However, in loops, the else clause has a unique behavior:

The else block is executed only if the loop completes all its iterations without encountering a break statement.
If the loop is exited early because of a break, the else block is skipped.

The else clause in loops (for and while) in Python is a bit unusual because most people associate else with if statements. In the context of loops, the else clause is executed only when the loop finishes normally, meaning it wasn’t interrupted by a break statement.

How It Works:

With a for loop:
- The else block runs if the loop completes all its iterations without hitting a break.
- If the loop is terminated by a break, the else block is skipped.
With a while loop:
- The else block runs if the while loop condition becomes False naturally.
- If the loop is terminated by a break, the else block is skipped.

Example with a `for` loop

Let’s say we’re searching for a specific number in a list.

# List of numbers
numbers = [1, 2, 3, 4, 5]

# Number we want to find
target = 6

# Iterate over the list
for num in numbers:
    if num == target:
        print("Found the target!")
        break
else:
    print("Target not found in the list.")

Explanation:

The loop checks each number to see if it matches the target.
If the number is found, the loop breaks, and the else clause is skipped.
If the loop finishes without finding the target (i.e., without a break), the else block runs, printing “Target not found in the list.”

Example with a `while` loop

# Counter
i = 1

# Loop condition
while i <= 5:
    if i == 3:
        print("Breaking the loop")
        break
    print(i)
    i += 1
else:
    print("Loop finished without breaking.")

Explanation:

The loop runs while i is less than or equal to 5.
If i equals 3, the loop breaks.
Since the loop is broken before it naturally ends, the else block is skipped.

Why Use the `else` Clause with Loops?

Using else with loops can be helpful when you’re performing a search or some operation where you want to know if the loop completed successfully or was interrupted by a break. It’s a clean way to handle scenarios where the loop might end early.

Example #: for..else

for x in range(3):
    print(x)
else:
    print('Final x = %d' % (x))

Match Statement (Python 3.10+)

The match statement offers a more concise way to handle multiple comparison cases.

def get_fruit_color(fruit):
    match fruit:
        case "apple":
            return "red"
        case "banana":
            return "yellow"
        case _:
            return "unknown"

Key Terms

for
while
range
pass
else
match
break
continue
f-string

Fix the errors in Python

To learn about Common Errors in Python, see Appendix A.

Mistaken Use of elif Instead of if [Python Quiz #43]

Code:

x = 7

if x > 5:
    print("x is greater than 5")
elif x > 0:
    print("x is positive")

Watch the Solution Now ✨:https://youtu.be/oQAvH8N1uPk

Infinite while Loop Due to Missing Update Statement [Python Quiz #44]

Problem Statement: Write a program that starts with a given positive integer and repeatedly prints its value, decreasing it by 1 in each iteration until it reaches 0. However, the initial code runs into an issue: the loop does not terminate because the value of the integer is never updated, leading to an infinite loop.

Code:

n = 10

while n > 0:
    print(n)

Mistake:
The loop will run infinitely because n is never updated, so n > 0 is always true.

Watch the Solution Now ✨

continue Misused in while Loop [Python Quiz #45]

Scenario: You are tasked with debugging a piece of Python code that uses a while loop. The goal of the loop is to print numbers from 0 to 4, skipping the number 2. However, the code as written enters an infinite loop when the value of i becomes 2.

Given Code:

i = 0

while i < 5:
    if i == 2:
        continue
    print(i)
    i += 1

Problem: The continue statement is misused in this code. When i == 2, the continue statement is executed, causing the loop to skip the i += 1 statement. As a result, i remains 2 indefinitely, leading to an infinite loop.

Task:

Identify the mistake in the code that causes the infinite loop.
Correct the code so that it successfully prints all numbers from 0 to 4, except for 2.

Expected Output:

Watch the Solution Now ✨

Incorrect Use of Multiple elif Conditions

Code:

score = 75

if score >= 90:
    print("A")
elif score >= 80:
    print("B")
elif score >= 70:
    print("C")
elif score >= 60:
    print("D")
elif score < 70:
    print("F")

Mistake:
The last elif block (elif score < 70) is redundant because the elif score >= 70 block already covers it.

Improved Code:

score = 75

if score >= 90:
    print("A")
elif score >= 80:
    print("B")
elif score >= 70:
    print("C")
elif score >= 60:
    print("D")
else:
    print("F")

The else block now correctly handles any score below 60.

Syntax Error: Missing Colon [Python Quiz #49]

if x > 5  # Missing colon here
  print("X is greater than 5")

Here’s another question:

Question:

The following code is intended to print the even numbers from 0 to 10, but it contains an error. Identify and fix the error.

for i in range(0, 11):
if i % 2 == 0:
    print(i)

Answer:

The code has an indentation error. The if statement needs to be indented to be part of the for loop.

Fixed Code:

for i in range(0, 11):
    if i % 2 == 0:
        print(i)

Explanation:

In Python, all statements inside a for loop and any nested statements (like if) need to be indented consistently. This indicates that they are part of the respective block.

Which of the following will NOT cause a syntax error in Python?

1st_variable = 10

if x == 10:
print("x is 10")

print("Hello World!"

print "Hello World!)

E) None

Incorrect if Statement Syntax

Code:

x = 10

if x > 5
    print("x is greater than 5")

Mistake:
The if statement is missing a colon (:) at the end.

Corrected Code:

x = 10

if x > 5:
    print("x is greater than 5")

Incorrect Indentation in if-else Statement

Code:

y = -3

if y > 0:
    print("y is positive")
    print("This is always printed")
else:
print("y is not positive")

Mistake:
The else block is not properly indented.

Corrected Code:

y = -3

if y > 0:
    print("y is positive")
    print("This is always printed")
else:
    print("y is not positive")

while Loop with Incorrect Condition

Code:

count = 10

while count > 10:
    print("This will never print")
    count -= 1

Mistake:
The loop condition count > 10 is false at the start, so the loop will never run.

Corrected Code:

count = 10

while count >= 0:
    print("Count:", count)
    count -= 1

for Loop with Incorrect Range

Code:

for i in range(1, 10, -1):
    print(i)

Mistake:
The step value in range(1, 10, -1) is negative, but the start value is less than the stop value, so this loop will not run.

Corrected Code:

for i in range(10, 0, -1):
    print(i)

This prints numbers from 10 to 1.

Using break Incorrectly in a Loop

Code:

for i in range(5):
    if i == 2:
        break
    else:
        print(i)

Mistake:
The else block is not correctly used here. It runs as part of each iteration, not after the loop.

Corrected Code:

for i in range(5):
    if i == 2:
        break
    print(i)
else:
    print("Loop completed without a break")

The else block will only run if the loop completes without a break.

try Block with Unhandled Exception

Code:

try:
    print(5 / 0)
except TypeError:
    print("A TypeError occurred")

Mistake:
The code raises a ZeroDivisionError, but the except block is only catching a TypeError.

Corrected Code:

try:
    print(5 / 0)
except ZeroDivisionError:
    print("You can't divide by zero!")

Misuse of continue Statement

Code:

for i in range(5):
    if i == 3:
        continue
        print("This will never be printed")
    print(i)

Mistake:
The print statement after continue will never be executed.

Corrected Code:

for i in range(5):
    if i == 3:
        continue
    print(i)

The code correctly skips printing 3 and continues with the next iteration.

Logical Error with if-elif Statements

Code:

z = 20

if z > 30:
    print("z is greater than 30")
elif z > 10:
    print("z is greater than 10")
else:
    print("z is less than 10")

Mistake:
The code will print "z is greater than 10" even though z is also greater than 30. This is logically correct, but not what might be intended if you want to check for ranges.

Corrected Code:

z = 20

if z > 30:
    print("z is greater than 30")
elif z > 20:
    print("z is greater than 20 but less than 30")
elif z > 10:
    print("z is greater than 10")
else:
    print("z is less than or equal to 10")

Now, this checks for more specific conditions.

What will be the output of the following code?

for i in range(5):
    print(i)
else:
    break

Incorrect Usage of pass in Control Flow

Code:

for i in range(5):
    if i == 2:
        pass
        print("This should not print")
    print(i)

Mistake:
The pass statement does nothing, but the print("This should not print") will still run.

Corrected Code:

for i in range(5):
    if i == 2:
        pass
    print(i)

Now, the loop will simply skip doing anything when i is 2, without any unintended behavior.

Improper Use of finally in Exception Handling

Code:

try:
    result = 10 / 0
finally:
    print("This will run no matter what.")
except ZeroDivisionError:
    print("You can't divide by zero!")

Mistake:
The finally block must come after except, not before.

Corrected Code:

try:
    result = 10 / 0
except ZeroDivisionError:
    print("You can't divide by zero!")
finally:
    print("This will run no matter what.")

These challenges are designed to highlight common mistakes that occur when working with control flow statements in Python. Working through these examples will help reinforce proper syntax and logical structure.

True/False (Mark T for True and F for False)

Multiple Choice (Select the best answer)

if statement (MCQs)

What is the syntax for a simple if statement in Python? [Python Quiz #50] - A) if x == 10: - B) for x in range(10): - C) while x < 10: - D) if (x == 10) then:

What is the output of the following code Python Quiz #16

x = 10
y = 5

if x == y * 2:
    print("True")
else:
    print("False")

- A) True
- B) False
- C) Error
- D) Nothing

Watch this video for the answer: https://youtube.com/shorts/ExDu2lwjd3c?si=VVq47sCNgRWd7l_i

What is the output of the following code? Python Quiz #31

x = 3
y = 5

if x == 3 and y != 5:
    print("True")
else:
    print("False")

- A) True
- B) False
- C) Syntax error
- D) Name error

Watch the video for the answer: https://youtube.com/shorts/7uAgT3_P4Oc?si=evBHSymYx2kVaEEk

What will be the output of the following code? Python Quiz #39
```
x = 10
if  5 < x < 15:
 print("x is between 5 and 15")
else:
 print("x is not between 5 and 15")
```
- A) x is between 5 and 15
- B) x is not between 5 and 15
- C) Error
- D) No output Watch the video for the answer:https://youtu.be/TkmqlDK8oCg
Which of the following correctly fixes the syntax error in the code below? Python Quiz #40

# fixes the error
x = 10
if x == 10
    print("x is 10")

- A) Remove the comment.
- B) Add a colon after `if x == 10`.
- C) Add parentheses around `x == 10`.
- D) Indent the print statement correctly.

Watch the video for the answer: https://youtu.be/3010E1WuHd8

Which of the following correctly represents the syntax of an if statement in Python?
- A) if condition { block of code }
- B) if(condition) { block of code }
- C) if condition: block of code
- D) None
What is the purpose of the else block in an if statement?
- A) To execute a code block when the if condition is True
- B) To execute a code block when the if condition is False
- C) To create an infinite loop
- D) To define a function
What happens when none of the conditions in an if-elif-else chain are True, and there is no else block?
- A) The program raises an error.
- B) The program executes the first if block.
- C) The program executes the last elif block.
- D) The program does nothing and continues to the next statement.
What will be the output of the following code?

x = 10
y = 5
if x < y:
    print("x is greater than y")

- A) "x is greater than y"
- B) "x is less than y"
- C) Nothing will be printed
- D) An error will occur

What happens if none of the conditions in an if-elif chain are True, and there is no else block?
- A) The program raises an error
- B) The program executes the first if block
- C) The program does nothing and continues to the next statement
- D) The program executes the last elif block
What will be the output of the following code?

number = 10
if number % 2 == 0:
    print("Number is even")
else:
    print("Number is odd")

- A) Number is odd
- B) Number is even
- C) Nothing
- D) Error

Which of the following is the correct way to compare if two variables are equal in an if statement?
- A) if x equals 5:
- B) if x == 5:
- C) if x = 5:
- D) if x := 5:
How can you check if a value is NOT equal to 10 in an if statement?
- A) if x != 10:
- B) if x <> 10:
- C) if x =! 10:
- D) if x not 10:
What does the following code snippet do? ```python if x > 0: print(“Positive”) elif x < 0: print(“Negative”) else: print(“Zero”)

    - A) Prints "Positive" if x is greater than 0, "Negative" if x is less than 0, and "Zero" if x is 0.
    - B) Prints "Positive" if x is less than 0, "Negative" if x is greater than 0, and "Zero" if x is 0.
    - C) Prints "Positive" if x is 0, "Negative" if x is greater than 0, and "Zero" if x is less than 0.
    - D) Causes an error because the conditions are conflicting.

11. **What is the correct syntax for an if-else statement?**
   - A) if condition:
            code block
   - B) if condition:
            code block
        else:
            code block
   - C) if condition:
            code block
        elif condition:
            code block
   - D) if condition:
            code block
        else:
            code block
        elif condition:
            code block

12. **What happens if none of the conditions in an if-elif-else block are true?**
    - A) The program terminates
    - B) The else block is executed
    - C) An error occurs
    - D) The program continues without executing any block

14. **What will be the output of the following code?**
   ```python
   num = 7
   if num % 2 == 0:
       print("Even")
   else:
       print("Odd")

- A) Even
- B) Odd
- C) Error
- D) No output

What will be the output of the following code?

score = 85
if score >= 90:
    print("Grade: A")
elif score >= 80:
    print("Grade: B")
elif score >= 70:
    print("Grade: C")
else:
    print("Grade: F")

- A) Grade: A  
- B) Grade: B  
- C) Grade: C  
- D) Grade: F

What is the output of the following code?

x = 5
if x > 10:
    print("Greater than 10")
elif x > 5:
    print("Greater than 5 but not greater than 10")
else:
    print("5 or less")

- A) Greater than 10  
- B) Greater than 5 but not greater than 10  
- C) 5 or less  
- D) No output

Answer: C

Which of the following is true about the elif statement?
- A) elif stands for “else if” and is used to check additional conditions after the if statement
- B) elif is the same as else
- C) elif must be followed by an else statement
- D) You can have multiple elif statements in one block

Answer: A, D

What will be the output of the following code?

y = 20
if y < 20:
    print("Less than 20")
elif y == 20:
    print("Equal to 20")
else:
    print("Greater than 20")

- A) Less than 20  
- B) Equal to 20  
- C) Greater than 20  
- D) None of the above

Answer: B

What will be the output of the following code snippet?

a = 10
b = 5
if a > b:
    if a > 0:
        print("a is positive")
    else:
        print("a is non-positive")
else:
    print("a is less than or equal to b")

- A) a is positive  
- B) a is non-positive  
- C) a is less than or equal to b  
- D) No output

Answer: A

Which of the following statements is false about if-elif-else statements in Python?
- A) elif statements are optional in an if-elif-else construct
- B) An if statement can be followed by multiple elif statements
- C) An else statement is mandatory in an if-elif-else construct
- D) An if statement can exist without elif or else

Answer: C

What will be the output of the following code?

x = 0
if x:
    print("True")
else:
    print("False")

- A) True  
- B) False  
- C) No output  
- D) Error

Answer: B

Truthy and Falsy Values in Python In Python, certain values are considered False when evaluated in a boolean context (like in an if statement). These values include:

None
False
0 (zero of any numeric type, including 0.0)
Empty sequences and collections (e.g., ‘’, (), [], {})
Any object that implements bool or len to return False or 0, respectively

Which of the following expressions can be used in an if condition to check if a number n is between 1 and 100 inclusive?
- A) if n > 1 and n < 100:
- B) if n >= 1 and n <= 100:
- C) if 1 <= n <= 100:
- D) if n == 1 or n == 100:

Answer: B, C

What will be the output of the following code?

z = 7
if z < 5:
    print("Less than 5")
elif z == 10:
    print("Equal to 10")
elif z > 5:
    print("Greater than 5 but not 10")
else:
    print("Something else")

- A) Less than 5  
- B) Equal to 10  
- C) Greater than 5 but not 10  
- D) Something else

Answer: C

What is the purpose of the else statement in an if-elif-else structure?
- A) To check another condition if the previous ones were false
- B) To execute a block of code if none of the previous conditions were true
- C) To execute a block of code if the previous conditions were true
- D) To end the if-elif-else structure

Answer: B

What will be the output of the following code?

x = 10
if x > 5:
    if x == 10:
        print("x is 10")
    else:
        print("x is greater than 5 but not 10")
else:
    print("x is 5 or less")

- A) x is 10  
- B) x is greater than 5 but not 10  
- C) x is 5 or less  
- D) No output

Answer: A

Which of the following is correct syntax for an if-elif-else statement in Python?

if x > y:
print("x is greater")
elif x == y:
print("x is equal to y")
else:
print("x is less")

if x > y:
    print("x is greater")
elif x == y:
    print("x is equal to y")
else:
    print("x is less")

if (x > y):
    print("x is greater")
elif (x == y):
    print("x is equal to y")
else:
    print("x is less")

if x > y:
    print("x is greater")
elif x == y
    print("x is equal to y")
else
    print("x is less")

Answer: B, C

What will be the output of the following code?

a = 3
b = 4
if a > b:
    print("a is greater")
elif a == b:
    print("a and b are equal")
else:
    print("b is greater")

- A) a is greater  
- B) a and b are equal  
- C) b is greater  
- D) No output

Answer: C

Which of the following statements will execute if n = 7?

if n < 5:
    print("n is less than 5")
elif n < 10:
    print("n is less than 10")
else:
    print("n is 10 or more")

- A) n is less than 5  
- B) n is less than 10  
- C) n is 10 or more  
- D) None of the above

Answer: B

Which keyword is used to check an additional condition if the initial if statement is False?
- A) else
- B) elif
- C) elseif
- D) if

Answer: B

What is the result of the following code?

x = 0
if x > 0:
    print("Positive")
elif x == 0:
    print("Zero")
else:
    print("Negative")

- A) Positive  
- B) Zero  
- C) Negative  
- D) No output

Answer: B

How many elif clauses can be included in an if-elif-else statement?
- A) One
- B) Two
- C) Unlimited
- D) None

Answer: C

What will be the output of the following code?

age = 20
if age < 18:
    print("Minor")
elif age >= 18 and age < 65:
    print("Adult")
else:
    print("Senior")

- A) Minor  
- B) Adult  
- C) Senior  
- D) No output

Answer: B

for loop (MCQs)

What is the output of the following code snippet in Python? Python Quiz #3

for i in range(10):
    if i % 2 == 0:
        print(i)

A) 0 1 2 3 4 5 6 7 8 9 B) 0 2 4 6 8 C) 2 4 6 8 D) IndentationError: expected an indented block

Watch the video for answer: https://bit.ly/3WKH9wE

What is the correct syntax for a for loop in Python?

A) for (int i = 0; i < 10; i++):
B) for i in range(10):
C) for i = 0 to 9:
D) for i in 10:

watch the video for the answer: https://youtu.be/2mhrDgBEp10

What will be the output of the following code? Python Quiz #36

for i in range(5):
  print(i * 2)

- A) 0 1 2 3 4
- B) 2 4 6 8 10
- C) 10 8 6 4 2
- D) 0 2 4 6 8

Watch this video for the answer: https://bit.ly/3WqjjEP

How many times is the print statement executed? Python Quiz #37
```
for i in range(3):
 for j in range(2):
     print(f"i = {i}, j = {j}")
```
- A) 3 times
- B) 5 times
- C) 6 times
- D) 9 times

Watch this video for the answer: https://youtu.be/CYeZI3uCiTI

What will the program output if the number variable is set to 5? ```python
Get user input

number = int(input(“Enter non-negative number:”))

if number < 0: print(“Factorial is not defined for negative numbers.”) result = None elif number == 0 or number ==1: result = 1 else: result = 1 for i in range(2, number + 1): result *= i

if result is not None: print(“Factorial of”, number, “is”, result)

- A) Factorial is not defined for negative numbers.
- B) Factorial of 5 is 5
- C) Factorial of 5 is 120
- D) Factorial of 5 is 24

**Watch this video for the answer:** [https://youtu.be/K5LV5I2hFg4](https://youtu.be/K5LV5I2hFg4)

6. **What will happen if the `number` variable is set to `0`?**

```python
# Get user input
number = int(input("Enter non-negative number:"))

if number < 0:
    print("Factorial is not defined for negative numbers.")
    result = None
elif number == 0 or number ==1:
    result = 1
else:
    result = 1
    for i in range(2, number + 1):
        result *= i

if result is not None:
    print("Factorial of", number, "is", result)

A) The program will raise an error.
B) The program will print “Factorial of 0 is 1”.
C) The program will print “Factorial is not defined for negative numbers.”
D) The program will print “Factorial of 0 is 0”.

Watch this video for the answer: https://youtu.be/K5LV5I2hFg4

What is the primary purpose of a for loop in Python?

- A) To define a function
- B) To iterate over a sequence
- C) To create a conditional statement
- D) To perform mathematical operations

In Python, what does the range() function do when used in a for loop? - A) Generates a sequence of numbers - B) Defines a list - C) Calculates the average - D) Determines the length of a string

How can you create a nested loop in Python?

- A) by using a loop inside another loop with proper indentation
- B) by using a loop inside another loop with parentheses
- C) by using a nested keyword before the inner loop
- D) by using a colon after the outer loop and before the inner loop

Answer: A

Question 4

Consider the following code:

total = 0
for i in range(1, 6):
    total += i
print(total)

What does this code accomplish?

A) It prints numbers from 1 to 5. B) It calculates the sum of numbers from 1 to 5. C) It prints the sum of numbers from 1 to 6. D) It calculates the sum of numbers from 0 to 5.

Explanation: The loop iterates over the range from 1 to 5 (inclusive), summing up the values. The total variable accumulates this sum.

Answer: B

Question 6

How can a for loop be used in a real-life scenario involving data processing?

A) To count the number of words in a large document. B) To open a web browser. C) To create a new file on the desktop. D) To turn off a computer.

Explanation: A for loop can be used to iterate through the words in a document to count them, making it useful for data analysis tasks.

Answer: A

Why might you use a for loop instead of manually performing repeated tasks?

- A) To reduce the chance of human error.
- B) To make the program run slower.
- C) To avoid using variables.
- D) To limit the program to one iteration.

Explanation: Using a for loop automates repetitive tasks, which helps prevent errors and saves time, especially when processing large datasets or performing repetitive calculations.

Answer: A

What does the following code print?

for x in range(5, 8):
    print(x)

- A) 5 6 7
- B) 5 6 7 8
- C) 4 5 6 7
- D) 5 6 7 8 9

Explanation: The range(5, 8) function generates numbers starting from 5 up to, but not including, 8.

Answer: A

What does the following code output?

for i in range(1, 4):
    for j in range(1, 3):
        print(i, j)

A) 1 1 1 2 2 1 2 2 3 1 3 2 B) 1 2 2 3 3 4 C) 1 3 2 3 3 3 D) 1 1 2 2 3 3

Explanation: This is a nested loop, where the outer loop runs from 1 to 3 (inclusive) and the inner loop runs from 1 to 2 (inclusive). It prints all combinations of i and j.

Answer: A

What will be the output of this code?

for i in range(3):
    print(i * i)

A) 0 1 4 B) 0 1 2 C) 1 4 9 D) 0 2 4

Explanation: The loop iterates over the range 0, 1, 2. For each iteration, it prints the square of the current index i.

Answer: A

What will the following code output?

for i in range(5, 10, 2):
    print(i)

A) 5 7 9

B) 5 6 7 8 9

C) 5 7 9 11

D) 5 7 8

Explanation: The range(5, 10, 2) generates numbers starting from 5 up to, but not including, 10 with a step of 2, resulting in 5, 7, and 9.

Answer: A

while loop (MCQs)

What is the output of the following code snippet in Python? Python Quiz #7

i = 1
while i < 10:
    print(i)
    i += 2

- A) 1 2 3 4 5 6 7 8 9
- B) 1 3 5 7 9
- C) 0
- D) IndentationError: expected an indented block

Watch the video for answer: https://youtube.com/shorts/zdLNmwO1u8Y

What is the output of the following code snippet in Python? Python Quiz #4

i = 0
while i < 5:
    print(i)
    i += 1
else:
    print("Done")

- A) 0 1 2 3 4 Done
- B) 0 1 2 3 Done
- C) SyntaxError: invalid syntax
- D) IndentationError: expected an indented block

Watch this video for the answer: https://youtube.com/shorts/9Zw-LuNX9h0

What is the output of the following code? Python Quzi #38

x = 10
while x > 0:
    print(x)
    x -= 2

- A) 9 7 5 3 1
- B) 10 8 6 4 2
- C) 10 9 8 7 6
- D) The code will run indefinitely.

Watch this video for the answer: https://bit.ly/3AdTqka

What is the output of the following code?

count = 0
while count < 3:
    print(count)
    count += 1

- A) 0 1 2
- B) 0 1
- C) 1 2 3
- D) The code will run indefinitely.

What will happen if you try to modify the loop variable within the body of a while loop?

(a) The loop will continue as normal. (b) The loop will terminate immediately. (c) The loop may behave unexpectedly, depending on how the variable is modified. (d) The loop will always run indefinitely.

What is the correct syntax for a while loop in Python?

A) while (condition): B) while condition {} C) while condition: D) while (condition) {}

What is the purpose of the else clause in a while loop?

(a) To execute a block of code if the loop condition is never true. (b) To execute a block of code if the loop completes without being terminated by a break statement. (c) To execute a block of code if the loop encounters an error. (d) The else clause cannot be used with a while loop.

What is the difference between pass and return statements in Python?3

A) pass does nothing and return exits the function B) pass exits the function and return does nothing C) pass and return both do nothing D) pass and return both exit the function Answer: A

How can you create an if-elif-else statement without using elif keyword in Python?2

A) by using nested if-else statements B) by using logical operators with if-else statements C) by using multiple if statements with indentation D) none of the above Answer: A

What is the difference between break and continue statements in Python?3

A) break terminates the loop and continue skips the current iteration B) break skips the current iteration and continue terminates the loop C) break and continue both terminate the loop D) break and continue both skip the current iteration Answer: A

What is the benefit of using control structures in programming languages?3

A) to make the code more modular and reusable B) to control the flow of execution based on certain parameters or conditions C) to implement various algorithms and logic in the code D) all of the above Answer: D

How can you create an if-else statement in one line in Python?2

A) by using a ternary operator with condition and values B) by using a lambda function with condition and values C) by using a colon after if block and before else block D) by using parentheses around if block and else block Answer: A

Loop Control Statements (break, continue, pass) (MCQs)

What is the output of the following code snippet in Python? [Python Quiz #5]
```
for i in range(5):
 if i == 3:
     continue
 print(i)
```
- A) 0 1 2 3
- B) 0 1 2 4
- C) SyntaxError: invalid syntax
- D) IndentationError: expected an indented block

Watch this video for answer: https://youtube.com/shorts/x7CIxqoqccY

What is the output of the following code snippet in Python? [Python Quiz #6]
```
for i in range(5):
 if i == 3:
     break
 print(i)
```
- A) 0 1 2
- B) 0 1 2 3
- C) 1 2 3
- D) 0 1 2 3 4

Watch this video for answer: https://youtube.com/shorts/XNLL6j-P61A

youtube@yasirbhutta

What is the output of the following code?

i = 0
while i < 5:
    i += 1
    if i == 3:
        break
    print(i)
else:
    print("Loop completed")

- A) 1 2
- B) 1 2 Loop completed
- C) 1 2 3
- D) 1 2 3 Loop completed

Watch the Video Tutorial for the Answer: https://youtu.be/LfF9CsyVRgU

How can you create a nested if statement in Python?2

A) by using elif keyword B) by using else keyword C) by indenting the inner if block under the outer if block D) by using parentheses around the inner if block Answer: C What is the purpose of a pass statement in Python?3

A) to skip a block of code that is not needed B) to indicate that a block of code is empty or not implemented yet C) to exit a loop or a function prematurely D) to pass a value or an argument to another function Answer: B

What is the syntax of a while loop in Python?1

A) while condition: statement B) while (condition): statement C) while condition do statement D) while (condition) do statement Answer: A

What is the difference between a break statement and a continue statement in Python?4

A) break terminates the loop, continue skips to the next iteration B) break skips to the next iteration, continue terminates the loop C) break exits the program, continue pauses the program D) break resumes the program, continue exits the program Answer: A

What are the three types of control structures in Python?

A) Sequential, Selection and Repetition B) Conditional, Looping and Branching C) Function, Class and Module D) Input, Output and Processing Answer: A

What is the keyword used to make a selection statement in Python?2

A) select B) if C) switch D) case Answer: B

What are the two types of iteration statements in Python?1

A) while and do-while B) for and foreach C) while and for D) do-while and foreach Answer: C

What are the three basic types of control structures in Python? a) sequence, selection, repetition b) input, output, processing c) function, class, module d) list, tuple, dict Answer: a) sequence, selection, repetition

Which control structure is used to execute a block of code only if a certain condition is true? a) if statement b) for loop c) while loop d) break statement Answer: a) if statement

Which control structure is used to execute a block of code for each item in an iterable object? a) if statement b) for loop c) while loop d) break statement Answer: b) for loop

#51 In Python, What is the output of this code?

name = “Ahmad” if name == “Ahmad”: print(“Hello, Ahmad”) elif name == “Ali”: print(“Hello, Ali”) else: print(“Hello, stranger”)

Ahmad Hello, Ahmad Hello, stranger Syntax Error

#39 Which keyword is used to break out of a loop in Python?

Watch the Video Tutorial for the Answer: https://youtu.be/LfF9CsyVRgU

#python #pythonpoll #MCQsTest #yasirbhutta

a) stop b) break c) end d) exit

Answer: b) break

#34 What is the output of the following code?

for i in range(5): if i == 3: continue print(i)

#python #pythonpoll #MCQsTest #yasirbhutta

a) 0 1 2 4 b) 0 1 2 3 c) 1 2 4 d) 0 1 2 3 4

Answer: a) 0 1 2 4

Which loop is best suited for iterating over a range of numbers?

a) for loop b) while loop c) do-while loop d) foreach loop Answer: a) for loop

Which of the following loops is guaranteed to execute at least once? a) for loop b) while loop c) do-while loop d) foreach loop Answer: c) do-while loop

#36 Which keyword is used to skip to the next iteration of a loop in Python?

Watch the Video Tutorial for the Answer: https://youtube.com/shorts/lf6SYOMIJv8?feature=share

#python #pythonpoll #MCQsTest #yasirbhutta

a) skip b) continue c) next d) go Answer: b) continue

Which of the following is not a looping statement in Python? a) for b) while c) repeat d) do-while

Exercises

if elif else statement Exercises

Problem 1: FizzBuzz

Problem Statement: Write a program that prints the numbers from 1 to n. But for multiples of 3, print “Fizz” instead of the number, and for the multiples of 5, print “Buzz”. For numbers which are multiples of both 3 and 5, print “FizzBuzz”.

Input:

The first and only line contains the integer n.

Output:

Print numbers from 1 to n, replacing multiples of 3 with “Fizz”, multiples of 5 with “Buzz”, and multiples of both with “FizzBuzz”.

Example:

Input:

Output:

1
2
Fizz
4
Buzz
Fizz
7
8
Fizz
Buzz
11
Fizz
13
14
FizzBuzz

Watch the Solution Now ✨

Check Positive, Negative, or Zero

# Write a program to check if a number is positive, negative, or zero.
number = int(input("Enter a number: "))

Even or Odd

# Write a program to check if a number is even or odd.
number = int(input("Enter a number: "))

Largest of Three Numbers

# Write a program to find the largest of three numbers.
a = int(input("Enter first number: "))
b = int(input("Enter second number: "))
c = int(input("Enter third number: "))

Grade Assignment

# Write a program to assign grades based on the score.
score = int(input("Enter your score: "))

Leap Year Check

# Write a program to check if a year is a leap year or not.
year = int(input("Enter a year: "))

Age Group Classification

# Write a program to classify age into child, teenager, adult, and senior.
age = int(input("Enter your age: "))

Temperature Description

# Write a program to describe the temperature (hot, warm, cold).
temperature = float(input("Enter the temperature: "))

Voter Eligibility

# Write a program to check if a person is eligible to vote.
age = int(input("Enter your age: "))

Password Strength Checker

# Write a program to check the strength of a password.
password = input("Enter your password: ")

Simple Calculator

# Write a simple calculator program using if-elif-else.
num1 = float(input("Enter first number: "))
num2 = float(input("Enter second number: "))
operation = input("Enter operation (+, -, *, /): ")

BMI Calculator

# Write a program to calculate BMI and categorize it (underweight, normal, overweight, obese).
height = float(input("Enter your height in meters: "))
weight = float(input("Enter your weight in kilograms: "))

Triangle Type Checker

# Write a program to check the type of a triangle (equilateral, isosceles, scalene).
a = float(input("Enter first side: "))
b = float(input("Enter second side: "))
c = float(input("Enter third side: "))

Day of the Week

# Write a program to print the day of the week based on a number (1 for Monday, 7 for Sunday).
day_number = int(input("Enter a number (1-7): "))

Letter Grade Assignment

# Write a program to convert a numerical score into a letter grade.
score = int(input("Enter your score: "))

Month Days

# Write a program to print the number of days in a given month.
month = int(input("Enter the month number (1-12): "))

Discount Calculator

# Write a program to calculate the discount on a product based on the price.
price = float(input("Enter the price of the product: "))

Character Checker

# Write a program to check if a character is a vowel or consonant.
char = input("Enter a character: ").lower()

Valid Triangle Checker

# Write a program to check if three given lengths can form a triangle.
a = float(input("Enter first side: "))
b = float(input("Enter second side: "))
c = float(input("Enter third side: "))

Multiples of Five

# Write a program to check if a number is a multiple of five.
number = int(input("Enter a number: "))

Alphabet Case Checker

# Write a program to check if an alphabet is uppercase or lowercase.
char = input("Enter a character: ")

Login System

# Write a simple login system that checks username and password.
username = input("Enter username: ")
password = input("Enter password: ")

Divisibility Check

# Write a program to check if a number is divisible by 3 and 5.
number = int(input("Enter a number: "))

Prime Number Checker

# Write a program to check if a number is prime.
number = int(input("Enter a number: "))

Digit or Alphabet Checker

# Write a program to check if a character is a digit or an alphabet.
char = input("Enter a character: ")

Fuel Efficiency

# Write a program to categorize fuel efficiency (excellent, good, average, poor).
mpg = float(input("Enter miles per gallon: "))

Odd or Even List

# Write a program to classify numbers in a list as odd or even.
numbers = [int(x) for x in input("Enter numbers separated by space: ").split()]

Quadratic Equation Solver

# Write a program to solve a quadratic equation and determine the nature of the roots.
a = float(input("Enter coefficient a: "))
b = float(input("Enter coefficient b: "))
c = float(input("Enter coefficient c: "))

User Age Validator

# Write a program to validate the age input by the user (must be between 0 and 120).
age = int(input("Enter your age: "))

Student Result System

# Write a program to check if a student passed or failed based on marks in three subjects.
marks1 = int(input("Enter marks in subject 1: "))
marks2 = int(input("Enter marks in subject 2: "))
marks3 = int(input("Enter marks in subject 3: "))

Shopping Cart Total

# Write a program to calculate the total cost of items in a shopping cart and apply discount if applicable.
item1 = float(input("Enter price of item 1: "))
item2 = float(input("Enter price of item 2: "))
item3 = float(input("Enter price of item 3: "))

For loop Exercises

Basic Exercises

Print “Python” 5 times: Write a for loop to print the word “Python” five times.
- Watch the Solution Now ✨
Print numbers 0 to 9: Write a for loop to print numbers from 1 to 10.
- Watch the Solution Now ✨
Print even numbers 2 to 20: Write a for loop to print all even numbers from 2 to 20.
Print each character in a string: Write a for loop to iterate through the string “Hello, World!” and print each character.
- Watch the Solution Now ✨
Find the factorial of a number: Write a for loop to calculate the factorial of a given number, e.g., 5! = 5 × 4 × 3 × 2 × 1.
- Watch the Solution Now ✨
Squares of numbers 1 to 5: Write a Python for loop that prints the square of each number from 1 to 5.
- Watch the Solution Now ✨
Count down from 10 to 1: Use a for loop to print numbers from 10 down to 1.
- Watch the Solution Now ✨
Calculate the sum of the first N natural numbers
- Watch the Solution Now ✨

Intermediate Exercises

Print the multiplication table for 5: Write a for loop to print the multiplication table for the number 5.
- Watch the Solution Now ✨
Print the first 10 Fibonacci numbers: Write a for loop to generate the first 10 numbers in the Fibonacci sequence.
Check if a number is prime: Write a for loop to check if a given number is prime.
Sum of digits of a number: Write a for loop to calculate the sum of the digits of a given number, e.g., 1234.
Print a pattern of stars: Use nested for loops to print the following pattern:
```
*
**
***
****
*****
```
Print odd numbers between 1 and 20: Write a for loop to print all odd numbers between 1 and 20.
Count vowels in a string: Use a for loop to count the number of vowels in the string “Hello, World!”.

Advanced Exercises

Generate a list of even numbers: Use a for loop to generate a list of even numbers between 1 and 20.
Print numbers divisible by 3 and 5 between 1 and 50: Use a for loop to print all numbers between 1 and 50 that are divisible by both 3 and 5.
Print a right-angle triangle of numbers: Use nested for loops to print the following pattern:
```
1
12
123
1234
12345
```
Print numbers that are multiples of 3 up to 30: Use a for loop to print all multiples of 3 up to 30.
Find numbers divisible by 7 and 11 between 1 and 100: Use a for loop to print all numbers between 1 and 100 that are divisible by both 7 and 11.
Calculate the harmonic sum of n numbers: Write a

While loop Exercises

How to Count Digits in a Positive Integer using Python
- Watch the Solution Now ✨
How to Count Occurrence of a Specific Digit in a Number using Python.
- Watch the Solution Now ✨

Loop Control Statements (break, continue, pass) Exercises

Write a Python program that runs an infinite loop using a while statement. Include a way to exit the loop by using the break statement.
- Watch the Solution Now ✨
Write a Python program using the continue statement in a loop to skip specific iterations, such as skipping over the numbers 0, 1, 2, and 4?
- Watch the Solution Now ✨

Mini Projects

Project #1: Simple Calculator

Write a Python program that allows the user to perform basic arithmetic operations (addition, subtraction, multiplication, and division) until they choose to exit. The program should take two numbers and an operation from the user, perform the calculation, and display the result.

Requirements:

The program should continuously prompt the user for two numbers and an operation.
If the user enters an invalid operation, display an error message and ask for input again.
The user should be able to exit the program by entering ‘exit’.
Handle division by zero gracefully.

Example:

# Function to perform calculations
def calculate(num1, num2, operation):
    if operation == 'add':
        return num1 + num2
    elif operation == 'subtract':
        return num1 - num2
    elif operation == 'multiply':
        return num1 * num2
    elif operation == 'divide':
        if num2 == 0:
            return "Error: Division by zero is not allowed."
        return num1 / num2
    else:
        return "Error: Invalid operation."

# Start the calculator loop
while True:
    user_input = input("Enter 'exit' to quit or press Enter to continue: ")
    
    if user_input.lower() == 'exit':
        print("Exiting the calculator. Goodbye!")
        break
    
    # Get user input for numbers and operation
    try:
        num1 = float(input("Enter the first number: "))
        num2 = float(input("Enter the second number: "))
        operation = input("Enter the operation (add, subtract, multiply, divide): ").lower()
        
        # Perform calculation
        result = calculate(num1, num2, operation)
        print(f"The result is: {result}")
    
    except ValueError:
        print("Error: Please enter valid numbers.")

Sample Output:

Enter 'exit' to quit or press Enter to continue: 
Enter the first number: 10
Enter the second number: 5
Enter the operation (add, subtract, multiply, divide): add
The result is: 15.0
Enter 'exit' to quit or press Enter to continue: 
Enter the first number: 10
Enter the second number: 0
Enter the operation (add, subtract, multiply, divide): divide
The result is: Error: Division by zero is not allowed.
Enter 'exit' to quit or press Enter to continue: exit
Exiting the calculator. Goodbye!

This task helps users practice using while loops for continuous input and performing basic arithmetic operations in Python.

Review Questions

for loop:

What is the difference between a for loop and a while loop in Python?
Can you use a for loop to iterate over a string?

if statement:

Can you have multiple elif blocks in an if-elif-else statement?
What is the purpose of nesting if statements?
References and Bibliography

[2] “ForLoop - Python Wiki,” Python.org, 2017. https://wiki.python.org/moin/ForLoop

Appendices

Appendix A: Common Errors in Python

Here are some common errors in Python, along with examples:

SyntaxError
- Description: This occurs when the code is not written correctly according to the Python syntax.
- Example:
```
if True
    print("Hello")
```
- Error Message: SyntaxError: invalid syntax
- Explanation: The colon (:) is missing at the end of the if statement.
IndentationError
- Description: Python relies on indentation to define the structure of code. If the indentation is incorrect, this error occurs.
- Example:
```
def my_function():
print("Hello, World!")
```
- Error Message: IndentationError: expected an indented block
- Explanation: The print statement should be indented under the function definition.
NameError
- Description: This occurs when a variable or function name is not defined.
- Example:
```
print(x)
```
- Error Message: NameError: name 'x' is not defined
- Explanation: The variable x is used before it is defined.
TypeError
- Description: This occurs when an operation is applied to an object of inappropriate type.
- Example:
```
result = "Hello" + 5
```
- Error Message: TypeError: can only concatenate str (not "int") to str
- Explanation: You cannot add a string and an integer directly.
IndexError
- Description: This happens when you try to access an element in a list using an index that is out of range.
- Example:
```
my_list = [1, 2, 3]
print(my_list[5])
```
- Error Message: IndexError: list index out of range
- Explanation: The list has only three elements, but you are trying to access the sixth element.
KeyError
- Description: This occurs when you try to access a key in a dictionary that does not exist.
- Example:
```
my_dict = {"name": "Alice"}
print(my_dict["age"])
```
- Error Message: KeyError: 'age'
- Explanation: The key 'age' does not exist in the dictionary.
AttributeError
- Description: This happens when you try to access an attribute or method that doesn’t exist for a particular object.
- Example:
```
my_list = [1, 2, 3]
my_list.append(4)
my_list.push(5)
```
- Error Message: AttributeError: 'list' object has no attribute 'push'
- Explanation: The push method does not exist for lists in Python; you should use append.
ValueError
- Description: This occurs when a function receives an argument of the right type but an inappropriate value.
- Example:
```
int("Hello")
```
- Error Message: ValueError: invalid literal for int() with base 10: 'Hello'
- Explanation: The string "Hello" cannot be converted to an integer.
ZeroDivisionError
- Description: This happens when you attempt to divide a number by zero.
- Example:
```
result = 10 / 0
```
- Error Message: ZeroDivisionError: division by zero
- Explanation: Division by zero is undefined in mathematics.
ImportError
- Description: This occurs when you try to import a module that doesn’t exist.
- Example:
```
 import non_existent_module
```
- Error Message: ImportError: No module named 'non_existent_module'
- Explanation: The module you are trying to import does not exist.

Understanding these common errors can help you debug your code more efficiently. Each error comes with a message that can guide you toward fixing the issue.

‌

In Python, an iterable object is an object that you can loop over using a “for” loop. It’s any object that can return its elements one at a time. ↩

Python: Flow Control Statements

Flow control statements

Conditional Statements (if, else, elif)

Example #1:

Example #2: Basic If-Else

Example #3: Checking Even or Odd

Example #4: Age Group Classification

Example #5: Grade Assignment

Example #6: Nested If-Else

Example #7: Temperature Check

Example #8: Voting Eligibility [video]

Example #9: Checking String Length

Task #1: Password Check

Task #2: Compare Two Numbers in Python

Task #3: Determine if a Number is Negative, Zero, or Positive

Task #4: Compare Two Input Numbers

Task #5: Age Checker

Task #6: Divisibility Check

Task #7: Voting Eligibility Check

loops

for loop

range() function:

Example #9: Print Numbers from 1 to 5

Example #10: Printing “Building the future, one line at a time.” 5 Times Using a for Loop

Example #11: Sum of Numbers from 1 to N

Task #8: Sum of Numbers in a Range

Task #9: Display Even Numbers in a Range

Example #12: Print Even Numbers from 2 to 10 and sum of even numbers

Task #10: Display Multiplication Tables**

Example #13: String as an iterable

Example #14: Lists as an iterable

Example #15: Loop over Lists of lists

Example #16 Nested Loops - Multiplication Tables

Why We Use Variables in For Loops

Example #17: Loop Through a List of Fruits in Python

Use of underscore in ‘For Loop’

Example #18: Using an Underscore in a Loop to Print “Hello” Multiple Times

while loop

Example #19: Print numbers from 1 to 10 using while loop

Example #20: Print “Hello, world!” 5 times using while loop

Task #10: Display Multiplication Tables**

Task #11: Sum Integers from 1 to 100 Using While Loop

Example #21: Sum of even numbers from 2 to 20 using while loop

Task #12: Calculate Squares of Numbers from 1 to 4 Using While Loop

Example #22: Prompt User for Input Until Blank Line is Entered

Example #23: Sum User-Entered Numbers Until Zero is Entered

Task #13: Sum User-Entered Numbers Until a Negative Number is Entered

Task #14: Number Guessing Game

Example #24: Infinite Loop Printing Messages with Counter

Loop Control Statements (break, continue, pass)

break

continue

pass

Example #: Using Break Statement in a Loop with Range

Example #: Print Odd Numbers Less Than 5 with Loop Control Statements (break, continue)

The else Clauses on Loops

Example with a for loop

Example with a while loop

Why Use the else Clause with Loops?

Example #: for..else

Match Statement (Python 3.10+)

Key Terms

Fix the errors in Python

Question:

Answer:

Fixed Code:

Explanation:

True/False (Mark T for True and F for False)

Multiple Choice (Select the best answer)

if statement (MCQs)

for loop (MCQs)

Get user input

Question 4

Question 6

while loop (MCQs)

Loop Control Statements (break, continue, pass) (MCQs)

Exercises

For loop Exercises

While loop Exercises

Loop Control Statements (break, continue, pass) Exercises

`break`

`continue`

`pass`

Example with a `for` loop

Example with a `while` loop

Why Use the `else` Clause with Loops?