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Python Variables - Beginner's Guide with Examples and Exercises

Learn Python variables with this beginner-friendly guide. Understand variable naming rules, assignments, and operations with examples and exercises. Perfect for students and professionals starting their Python journey.

2.1 Variables

Storage containers for data (numbers, text, etc.).

2.2 What is a variable

A variable is a named storage location in a computer’s memory that is used to hold data or values. It allows programmers to store and manipulate data within a program.

Purpose: Variables provide a way to store and manage data that can be used and manipulated throughout a program. They make programs more flexible and allow for dynamic data storage.

Assignment statement: in Python is used to assign a value to a variable. Its primary purpose is to store and manage data within a program.

Imagine variables as labeled boxes:

You have boxes for storing different things (numbers, words, etc.).
Each box has a name (label) to identify what’s inside.
You can put things in, take them out, and change what’s inside.

2.3 Variable names

In Python, valid variable names must adhere to the following rules:

Begin with a letter or an underscore: The first character of a variable name must be a letter (a-z, A-Z) or an underscore (_).
Followed by letters, digits, or underscores: After the first character, the variable name can contain letters, digits (0-9), or underscores.
Case-sensitive: Variable names are case-sensitive. For example, myVariable and myvariable would be considered different variables.
No reserved keywords: Variable names cannot be Python reserved keywords (e.g., if, for, while, class, etc.).

video:Function and Variable Naming |Python Best Practices video:Python Variables and Assignment video: Meaningful Variable Names | Python Best Practices video: Asterisk (*) in Variable Assignment

Example #1: Storing a name

name = "Muhammad Hamza"
print(name)

Example #2: Tracking a score:

score = 0
score = score + 10 # adds 10 to the score
print(score)

Example #3: Remembering a favorite color

favorite_color = "blue" #stores "blue"  in variable
print(favorite_color)

Example #4: Calculating the area of a rectangle

length = 10
width = 5

# calculates the area
area = length * width
print(area)

Example 5: How to assign multiple values to multiple variables?

Example 6: How to Swap Variables Without a Third Variable in Python

Example 7: Calculate the Area of a Circle with Radius

Example 8: Python Variable Names: Case-Sensitive? Avoid This Coding Mistake!

Key Points:

Choose meaningful names: Use names that describe what the variable stores (e.g., pizza_slices instead of x).
- video: Meaningful Variable Names | Python Best Practices
Assign values using =: The equals sign is used to put a value into a variable.
Change values: You can update a variable’s value later in your code.
Use variables in calculations and operations: Variables can be used just like regular numbers or text in expressions.
Think of variables as placeholders: They hold information that can change as your program runs.

Key Terms

Fix the Errors!

Using an undefined variable

name = "Ahmad"
print(f"Hello, {lastname}")  # lastname not defined

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

Variable names in Python are case-sensitive.
In Python, variables must be declared with a specific data type before they can be used.
The statement x = 5 both creates the variable x and assigns it the value 5.

Answer Key (True/False):

True
False
True

Multiple Choice (Select the best answer)

What is a variable in Python?
- A) A reserved word in Python
- B) A placeholder for storing data values
- C) A function that prints data
- D) A built-in library in Python
Which statement best describes a variable in Python?
- A) A variable can hold multiple values at once.
- B) A variable must be declared with a data type.
- C) A variable is a name that refers to a value.
- D) A variable is used only in loops.
What is the output of the following code?
```
x = 10
print(x)
```
- A) 10
- B) x
- C) Error
- D) None
Which of the following is not true about variables in Python?
- A) Variables can be reassigned to different data types.
- B) Variables must start with a letter or an underscore.
- C) Variables are case-sensitive.
- D) Variables must be declared before use.
What will be the output of the following code? [Python Quiz #76]
```
x = 5
y = x
x = 7
print(y)
```
- A) 7
- B) 5
- C) 0
- D) None
Why is it important to use meaningful variable names?
- A) It is required by the Python interpreter.
- B) It helps make the code more readable and maintainable.
- C) It increases the execution speed of the program.
- D) It is necessary for the code to run without errors.
What will be the output of the following code? [Python Quiz #77]
```
a = 1
b = a
a = a + 1
print(a, b)
```
- A) 1 1
- B) 2 1
- C) 1 2
- D) 2 2
Which of the following is a valid variable name in Python?
- A) 2ndValue
- B) value#2
- C) _value2
- D) value-2
Which of the following is a correct way to declare a variable in Python?
- A) int x = 5
- B) x = 5
- C) declare x = 5
- D) var x = 5
What is the output of the following code? [Python Quiz 78]
```
   x = 5
   y = "Hello"
   print(x + y)
```
- A) 5Hello
- B) Hello5
- C) TypeError
- D) Hello 5
Which of the following is not a valid variable name in Python?
- A) my_var
- B) _var
- C) 2var
- D) var2
Which of the following statements is true about variable assignment in Python?
- A) Variables must be declared before they are assigned a value.
- B) Variables are created when they are first assigned a value.
- C) Variable names must begin with a number.
- D) Python variables must be declared with a type.

38 What is the purpose of declaring a variable in Python?

a) To reserve memory space for the variable b) To give the variable a name c) To initialize the variable with a value d) All of the above Answer: d

Answer key (Mutiple Choice):

B) A placeholder for storing data values
C) A variable is a name that refers to a value.
A) 10
D) Variables must be declared before use.
B) 5
B) It helps make the code more readable and maintainable.
B) 2 1
C) _value2
B) x = 5
C) TypeError
- Explanation: In Python, the + operator is used for both arithmetic addition and string concatenation. However, it cannot be used to add an integer and a string directly. The code provided attempts to add an integer (x = 5) to a string (y = “Hello”), which is not a valid operation and will result in a TypeError.
C) 2var
- Explanation: In Python, variable names must start with a letter or an underscore and cannot start with a number. Thus, my_var, _var, and var2 are valid, but 2var is not.
B) Variables are created when they are first assigned a value.
A) 5

Fill in the Blanks

Variable names in Python must start with a letter or an ____.
Variables in Python are ____, meaning they can change type when assigned a new value.
The assignment operator in Python is the ____ symbol.

Answer Key (Fill in the Blanks):

underscore (_)
dynamic
equals (=)

Exercises

Exercise 1: Basic Variable Assignment

Create a variable called name and assign your name to it.
Create a variable called age and assign your age to it.
Create a variable called city and assign the city you live in to it.
Print all three variables.

Exercise 2: Variable Reassignment

Create a variable called favorite_color and assign your favorite color to it.
Print the value of favorite_color.
Reassign a new color to favorite_color.
Print the new value of favorite_color.

Exercise 3: Variable Operations

Create two variables called a and b and assign them the values 5 and 10, respectively.
Create a new variable called sum and assign it the value of a plus b.
Create a new variable called difference and assign it the value of a minus b.
Create a new variable called product and assign it the value of a times b.
Print the values of sum, difference, and product.

Exercise 4: String Concatenation

Create a variable called first_name and assign your first name to it.
Create a variable called last_name and assign your last name to it.
Create a new variable called full_name and assign it the value of first_name concatenated with last_name (with a space in between).
Print the value of full_name.

Example Solution:

first_name = "Alice"
last_name = "Johnson"

full_name = first_name + " " + last_name
print(full_name)

Exercise 5: Input and Variables

Use the input() function to get the user’s name and store it in a variable called user_name.
Use the input() function to get the user’s age and store it in a variable called user_age.
Print a message saying “Hello [user_name], you are [user_age] years old.”

Example Solution:

user_name = input("Enter your name: ")
user_age = input("Enter your age: ")

print("Hello", user_name + ", you are", user_age, "years old.")

Calculate the Area of a Circle with Radius Example Solution
How to Swap Variables Without a Third Variable in Python. Example Solution
How to assign multiple values to multiple variables. Example Solution

Review Questions

1. What is a variable in computer programming? Answer: A variable is a named storage location in a computer’s memory that is used to hold data or values. It allows programmers to store and manipulate data within a program.

2. What is the purpose of using variables in programming? Answer: Variables provide a way to store and manage data that can be used and manipulated throughout a program. They make programs more flexible and allow for dynamic data storage.

3. What is the difference between declaring and initializing a variable? Answer: Declaring a variable involves specifying its name and data type, while initializing a variable means giving it an initial value. Initialization usually follows declaration but is not always required.

What is a variable in computer programming? Give examples of integer, string, float, and Boolean variables.

References and Bibliography

🧠 Practice & Progress

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