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.
In Python, a dictionary is a collection of key-value pairs. Each key in a dictionary is unique, and it is associated with a value. Dictionaries are used to store data values like a map or a real-life dictionary where each word (key) has a definition (value). They are mutable, meaning you can change, add, or remove items after the dictionary is created.
You create a dictionary using curly braces {} with keys and values separated by a colon :. Multiple key-value pairs are separated by commas.
# Example of a dictionary
student = {
"name": "John",
"age": 20,
"courses": ["Math", "Science"]
}
You can access the value associated with a specific key by using square brackets [] or the get() method.
# Accessing values
print(student["name"]) # Output: John
print(student.get("age")) # Output: 20
You can add a new key-value pair or update an existing one by assigning a value to the key.
# Adding a new key-value pair
student["grade"] = "A"
# Updating an existing value
student["age"] = 21
You can remove elements using the pop() method or del keyword.
# Removing a specific key-value pair
student.pop("grade")
# Using del keyword
del student["age"]
You can loop through keys, values, or both using a for-loop.
# Looping through keys
for key in student:
print(key)
# Looping through values
for value in student.values():
print(value)
# Looping through key-value pairs
for key, value in student.items():
print(f"{key}: {value}")
Here’s a full example demonstrating how to use a dictionary:
# Creating a dictionary
student = {
"name": "John",
"age": 20,
"courses": ["Math", "Science"]
}
# Accessing and updating data
print(student["name"]) # Output: John
student["age"] = 21
print(student["age"]) # Output: 21
# Adding a new key-value pair
student["grade"] = "A"
# Removing a key-value pair
student.pop("courses")
# Looping through dictionary
for key, value in student.items():
print(f"{key}: {value}")
name: John
age: 21
grade: A
This makes dictionaries a powerful tool for organizing and accessing data in Python!
Answer Key (True/False):
a = ('34.5')
print(type(a))
Watch the video for the answer: https://youtube.com/shorts/uMtHVgPSymw
tup2= 3,4,5
nested_tup = tup2, (6,7)
print(nested_tup)
Watch the video for the answer: Learn 5 Easy Ways to Create Tuples in Python
tup4 = tuple('python')
print(tup4)
- A) 'python'
- B) ['python']
- C) ('python')
- D) ('p', 'y', 't', 'h', 'o', 'n')
Watch the video for the answer: Learn 5 Easy Ways to Create Tuples in Python
What is the output of the following code? [Python Quiz #18]
a = [1, 2, 3]
b = [4, 5, 6]
c = a + b
print(c)
Watch the video for the answer: https://youtube.com/shorts/rEDmm9ry7wE?si=ce2iYVXHbCEjLm6W
What is the output of the following code? [Python Quiz #19]
a = [1, 2, 3, 4]
b = a
b[0] = 0
print(a)
Watch the video for the answer: [https://youtu.be/ZWB4dfUYz1k?si=aYNoLd_81-9oLfR](https://youtu.be/ZWB4dfUYz1k?si=aYNoLd_81-9oLfR)
What is the output of the following code? [Python Quiz #20]
my_list = [1, 2, 3, 4, 5]
print(my_list[1::2])
Watch the video for the answer: https://youtube.com/shorts/UH5znVEFehI
What is the output of the following code? [Python Quiz #21]
my_list = [8, 9, 11, 12]
print(my_list[1:-1])
Watch the video for the answer: https://youtube.com/shorts/PBBnTGfFm4o?si=Z1TlMu24412nVKG_
What is the output of the following code? [Python Quiz #26]
my_list = [
"apple",
"banana",
"cherry"
]
print(len(my_list))
Options:
Watch the video for the answer: https://youtube.com/shorts/t7SVFVPrPlk?si=h9nAfaOPofOLnwu4
What is the output of the following code? [Python Quiz #32] Code Explanation:
a = [1, 2, 3] # Creates a list named 'a' with elements 1, 2, and 3
b = a.copy() # Creates a copy of list 'a' and assigns it to 'b'
a[0] = 4 # Modifies the first element of list 'a' to 4
print(b) # Prints the contents of list 'b'
Watch the video for the answer: https://youtube.com/shorts/Jub8TgDntRQ?si=wt8IPaFgr4BMEk7E
What is the output of the following code? Python Quiz #34
a = [1, 2, 3]
b = a[:]
b[0] = 4
print(a)
Watch the video for the answer: https://youtube.com/shorts/rslioE6VWOQ
What is the output of the following code? [Python Quiz #35] Code:
my_list = [1, 2, 3, 4, 5]
for i in range(len(my_list)):
my_list[i] *= 2
print(my_list)
Options:
Watch the video for the answer: https://youtube.com/shorts/QffZTQasQSs?si=6ZW4auXECcvTGQgn
What is the output of the following code? [Python Quiz #25]
my_dict = {
'a': 1, 'b': 2,
'c': 3
}
for key in my_dict:
print(my_dict[key])
- A) abc
- B) 123
- C) {1, 2, 3}
- D) {a, b, c}
Watch the video for the answer: https://youtube.com/shorts/wofaOXA0SVA?si=EY4-_ndR8_qbB6zF
What is the output of the following code? [Python Quiz #65]
my_dict = {"name": "Alice", "age": 30}
print(my_dict["city"])
What will happen when you run this code?
- A) It will print `None`.
- B) It will print an empty string `""`.
- C) It will raise a `KeyError`.
- D) It will print `city`.
Correct Answer:
C. It will raise a KeyError.
What is the output of the following code?
my_set = {1, 2, 3}
result = my_set.add(4)
print(result)
- A) Error
- B) None
- C) {1, 2, 3, 4}
- D) {4}
What is the data type of the following value? {1, 2, 3} a) list b) tuple c) set d) dict
Answer: c) set
What is the data type of the following value? {1, 2, 3} a) list b) tuple c) set d) dict
Answer: c) set
What is the data type of the following value? (1, 2, 3) a) list b) tuple c) set d) dict
Answer: b) tuple
What is the data type of the following value? {“name”: “Alice”, “age”: 25} a) list b) tuple c) set d) dict
Answer: d) dict
What is the data type of the following value? [1, 2, 3] a) list b) tuple c) set d) dict
Answer: a) list
What is the correct way to create a set in Python?
a) set = [1, 2, 3] b) set = (1, 2 ,3) c) set = {1, 2 ,3} d) set = <1, 2 ,3>
Answer: c) set = {1, 2 ,3}
#58 What is the correct way to create a loop in Python?
a) for i in range(10): b) while i < 10: c) repeat i = 0 to 9: d) either a or b
Answer: d) either a or b
#53 What is the correct way to create a dictionary in Python?
a) dict = [key: value] b) dict = (key: value) c) dict = {key: value} d) dict = <key: value>
Answer: c) dict = {key: value}
#52 What is the correct way to create a list in Python?
a) list = [1, 2, 3] b) list = (1, 2, 3) c) list = {1, 2, 3} d) list = <1, 2, 3>
Watch this video for the answer:
#47 In Python, What is the output of the following code?
a = [1, 2, 3, 4] b = [5, 7, 4, 9,2] print (a[-1] in b)
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True False Error None
#35 What is the output of the following code?
def fun(arr): arr = arr[::-1]
arr = [1,2,3,4,5] fun(arr) print(arr)
Watch the Video Tutorial for the Answer: https://youtube.com/shorts/Ix-h6WR-vQM?feature=share
#python #pythonpoll #MCQsTest #yasirbhutta
[1,2,3,4,5] [5,4,3,2,1] [] Error
Answer: A.
#24 What is the syntax to create a union of two sets in Python?
Watch the Video Tutorial for the Answer: https://youtu.be/YDyCNYCUK9A
#python #pythonpoll #MCQsTest #yasirbhutta
a. set1 + set2 b. set1.union(set2) c. set1 & set2 d. set1.merge(set2)
Answer: b. set1.union(set2)
#26 What is the result of the following code?
set1 = {1, 2, 3} set2 = {3, 4, 5} set3 = set1.union(set2) print(set3)
Watch the Video Tutorial for the Answer: https://youtu.be/YDyCNYCUK9A
#python #pythonpoll #MCQsTest #yasirbhutta
a. {1, 2, 3} b. {3, 4, 5} c. {1, 2, 3, 4, 5} d. {3} Answer: c. {1, 2, 3, 4, 5}
Is it possible to use the union operator | to combine sets with different data types? a. Yes b. No Answer: b. No
#25 Can the union of two sets contain duplicates?
Watch the Video Tutorial for the Answer: https://youtu.be/YDyCNYCUK9A
#python #pythonpoll #MCQsTest #yasirbhutta
a. Yes b. No Answer: b. No
#27 What happens when you try to add an element to a set that already exists in the set?
Watch the Video Tutorial for the Answer: https://youtu.be/YDyCNYCUK9A
#python #pythonpoll #MCQsTest #yasirbhutta
a. A TypeError occurs b. The element is added as a duplicate c. Nothing happens, the element is not added
Answer: c. Nothing happens, the element is not added.
What is the output of the following code?
list1 = [10,20,10,’10’,20] set1 = set(list1) print(set1)
5 3 2 4 Answer: B) 3
What is the output of the following code?
set1 = {1,2,3} set2 = {1,2,3} print(*(set1+set2))
Error {2,4,6} [2,4,6] [1,2,3]
Answer: A) error + operator is not supported for set
What does the “in” operator do in Python? a) check if a value is present in a list b) check if a value is equal to another value c) check if a variable is defined Answer: a) check if a value is present in a list
Can the “in” operator be used with dictionaries in Python? a) yes b) no Answer: a) yes
How would you check if the value “dog” is in the list [‘cat’, ‘dog’, ‘elephant’] using the “in” operator? a) ‘dog’ in [‘cat’, ‘dog’, ‘elephant’] b) [‘dog’] in [‘cat’, ‘dog’, ‘elephant’] Answer: a) ‘dog’ in [‘cat’, ‘dog’, ‘elephant’]
Can the “in” operator be used to check if an element is present in a set in Python? a) yes b) no Answer: a) yes
How would you check if the value “dog” is in the set {‘cat’, ‘dog’, ‘elephant’} using the “in” operator? a) ‘dog’ in {‘cat’, ‘dog’, ‘elephant’} b) {‘dog’} in {‘cat’, ‘dog’, ‘elephant’} Answer: a) ‘dog’ in {‘cat’, ‘dog’, ‘elephant’}
#14 Is the “in” operator faster for checking if an element is present in a set compared to a list in Python?
https://lucasmagnum.medium.com/pythontip-list-vs-set-performance-experiments-dfbe4f72d47f
a) yes b) no Answer: a) yes
#13 What does the “in” operator do in Python?
a) check if a value is present in a list b) check if a value is equal to another value c) check if a variable is defined Answer: a) check if a value is present in a list
Can the “in” operator be used with dictionaries in Python?
a) yes b) no Answer: a) yes
How would you check if the value “dog” is in the list [‘cat’, ‘dog’, ‘elephant’] using the “in” operator?
a) ‘dog’ in [‘cat’, ‘dog’, ‘elephant’] b) [‘dog’] in [‘cat’, ‘dog’, ‘elephant’] Answer: a) ‘dog’ in [‘cat’, ‘dog’, ‘elephant’]
What is the operator used to check if an element is present in a set in python?
in contains has exit
Answer: A) in
What is the output of the following code?
t=(1,2,4,3) t[1:3] a) (1, 2) b) (1, 2, 4) c) (2, 4) d) (2, 4, 3)
#8 What is the output of the following code?
z=set(‘stri$ng’) print(‘r’ in z)
Python YouTube Playlist: https://www.youtube.com/playlist?list=PLKYRx0Ibk7Vi-CC7ik98qT0VKK0F7ikja
a) Error b) True c) False d) No output
Which of the following is a Python tuple?
Python YouTube Playlist: https://www.youtube.com/playlist?list=PLKYRx0Ibk7Vi-CC7ik98qT0VKK0F7ikja
a) {1, 2, 3} b) {} c) [1, 2, 3] d) (1, 2, 3)
#9 Which of the following Python statements will result in the output: 6
A = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]
Python YouTube Playlist: https://www.youtube.com/playlist?list=PLKYRx0Ibk7Vi-CC7ik98qT0VKK0F7ikja
a) A[2][1] b) A[1][2] c) A[3][2] d) A[2][3]
Answer: b Explanation: The output that is required is 6, that is, row 2, item 3. This position is represented by the statement: A[1][2].
11# Which of the following statements is used to create an empty set in Python?
related video:https://youtube.com/shorts/nmI7BGXPA4I
a) ( ) b) [ ] c) { } d) set() Explanation: { } creates a dictionary not a set. Only set() creates an empty set.
#15 What method is used to add an element to the end of a list in Python?
Watch the Video Tutorial for the Answer:https://youtu.be/x98wvk-4MHw
#python #pythonpoll #MCQsTest
A) append() B) insert() C) extend() D) append_list() Answer: A) append()
#16 How do you add an element to a specific index in a list in Python?
Watch the Video Tutorial for the Answer: https://youtu.be/x98wvk-4MHw
#python #pythonpoll #MCQsTest
A) add_index() B) insert() C) extend() D) append() Answer: B) insert()
#17 What function is used to remove the last element from a list in Python?
Watch the Video Tutorial for the Answer:https://youtu.be/x98wvk-4MHw
#python #pythonpoll #MCQsTest #yasirbhutta
A) del_last() B) remove_last() C) pop() D) delete_end() Answer: C) pop()
#18 How can you remove the first occurrence of an element from a list in Python?
Watch the Video Tutorial for the Answer: https://youtu.be/x98wvk-4MHw
#python #pythonpoll #MCQsTest #yasirbhutta
A) remove() B) delete_first() C) pop_first() D) del_first() Answer: A) remove()
What is the output of the following code?
list1 = [12,98,23,70,66] list1[1:4] = [20] print(list1)
[12,20,66] [12,20,23,70,66] [12,98,23,20,66] Error
Which of the following is not a core data type in Python? a) List b) Tuple c) Dictionary d) Class
How would you create a tuple with only one element?
a) my_tuple = (1,) b) my_tuple = (1) c) my_tuple = [1] d) my_tuple = {1}
What is the result of the following code?
x = [1, 2, 3] y = x y[1] = 4 print(x)
a) [1, 2, 3] b) [1, 4, 3] c) [4, 2, 3] d) [1, 2, 4]
What is the result of the following code?
x = [1, 2, 3] y = x y = [4, 5, 6]
print(x) a) [1, 2, 3] b) [4, 5, 6] c) [1, 4, 5, 6] d) [4, 5, 6, 1, 2, 3]
How would you add an element to the end of a list in Python? a) list.append(element) b) list += element c) list.push(element) d) list = list + [element]
#5 What is the result of the following code?
x = {1: ‘a’, 2: ‘b’, 3: ‘c’} y = x.copy() y[1] = ‘d’ print(x)
related video: https://youtube.com/shorts/PXp9uzvKFdU?feature=share
a) {1: ‘a’, 2: ‘b’, 3: ‘c’} b) {1: ‘d’, 2: ‘b’, 3: ‘c’} c) {1: ‘d’, 2: ‘b’, 3: ‘c’, 4: ‘d’} d) {1: ‘a’, 2: ‘b’, 3: ‘c’, 1: ‘d’}
How do you create an empty tuple in Python?
related video: https://youtu.be/nGIWcYXj580
a) tuple() b) {} c) () d) [] Answer: c) ()
How do you create a tuple with multiple elements in Python? related video: https://youtu.be/QpRiHuQycXg
a) tuple(1, 2, 3) b) (1, 2, 3) c) {1, 2, 3} d) [1, 2, 3] Answer: b) (1, 2, 3)
What is the correct way to create a tuple with a single element in Python? related video: https://youtu.be/nGIWcYXj580
a) tuple(1) b) (1,) c) {1} d) [1] Answer: b) (1,)
How do you add an element to an existing tuple in Python? a) tuple.append(element) b) tuple + (element,) c) tuple.extend(element) d) Tuples are immutable, so it is not possible to add an element to an existing tuple. Answer: d) Tuples are immutable, so it is not possible to add an element to an existing tuple.
How do you remove an element from a tuple in Python? a) tuple.remove(element) b) tuple.pop(element) c) Tuples are immutable, so it is not possible to remove an element from a tuple. d) del tuple[element] Answer: c) Tuples are immutable, so it is not possible to remove an element from a tuple.
What is the output of this code in PYTHON? list1=[1,2,3,4,5] print(list1[:4].pop())
[1,2,3,4] 5 [1,2,3,5] 4
What is the output of this code in PYTHON? list1=[1,2,34,5] print(list1[:4].pop())
[1,2,3,4] 5 [1,2,3,5] 4
Answer key (Mutiple Choice):
Answer Key (Fill in the Blanks):
[1] B. E. Prep, “Difference Between Mutable and Immutable in Python | Mutable vs Immutable Objects,” BYJU’S Exam Prep, Sep. 24, 2023. https://byjusexamprep.com/gate-cse/difference-between-mutable-and-immutable (accessed Jul. 27, 2024).
Here’s an expanded list of 50 exercises designed to help beginners understand and practice using for loops in Python. These exercises cover a variety of basic, intermediate, and advanced concepts to provide a comprehensive learning experience.
Print elements of a list: Use a for loop to print each element in the list [10, 20, 30, 40, 50].
for loops to print each element of a 2x2 matrix, e.g., [[1, 2], [3, 4]].for loop to find the largest number in the list [34, 78, 23, 89, 12].for loop to remove duplicates from the list [1, 2, 2, 3, 4, 4, 5].for loop to calculate the average of numbers in the list [10, 20, 30, 40, 50].for loop to transpose a 2x3 matrix, e.g., [[1, 2, 3], [4, 5, 6]] should become [[1, 4], [2, 5], [3, 6]].for loop to find the common elements in the lists [1, 2, 3, 4] and [3, 4, 5, 6].for loop to flatten the list [[1, 2], [3, 4], [5, 6]] into [1, 2, 3, 4, 5, 6].for loop to print all the indexes of the list [10, 20, 30, 40, 50].for loop to create a list of the first 10 square numbers.for loop to print numbers from the list [5, 12, 17, 9, 3, 21] that are greater than 10.for loop to calculate the sum of all even numbers in the list [1, 2, 3, 4, 5, 6, 7, 8, 9, 10].for loop to calculate the product of all numbers in the list [1, 2, 3, 4].for loop to find the smallest number in the list [34, 78, 23, 89, 12].for loop to convert the list [0, 10, 20, 30, 40] to Fahrenheit using the formula (Celsius * 9/5) + 32.Reverse the elements of a list: Write a for loop to reverse the elements of the list [1, 2, 3, 4, 5].
for loop to calculate the sum of the squares of numbers in the list [1, 2, 3, 4, 5].for loop to find the common elements in the lists [1, 2, 3, 4, 5] and [4, 5, 6, 7, 8].for loop to count the occurrences of each element in the list [1, 2, 2, 3, 3, 3, 4, 4, 4, 4].for loop to create a dictionary where keys are numbers from 1 to 5 and values are their squares.for loop to transpose the matrix [[1, 2, 3], [4, 5, 6], [7, 8, 9]].What is the output of the following code? Python Quiz #23
a = [1, 2, 3, 4, 5]
for i in range(0, len(a), 2):
print(a[i])
Watch the video for the answer: https://youtube.com/shorts/yrTnxNkrXH4?si=EUAzZiONKORP4nIU
What is the output of the following code?
fruits = ["Apple", "Banana", "Cherry"]
for i, fruit in enumerate(fruits):
if i == 1:
print(fruit)
related video: https://youtu.be/-FErgsl9njQ
Which of the following is the correct way to iterate over elements in a list using a for loop? a. for item in my_list: b. for i = 0; i < len(my_list): c. for element = my_list: d. for (i, item) in enumerate(my_list):
How can you iterate over both the index and elements of a list using a for loop? a. for i in my_list: b. for (i, element) in enumerate(my_list): c. for element in range(my_list): d. for index, element in my_list:
What is the output of the following code?
numbers = [1, 2, 3, 4, 5]
for x in numbers:
print(x * 2)
a. 2 4 6 8 10 b. 1 2 3 4 5 c. 1 4 9 16 25 d. 2 4 8 16 32
How many times will the following loop execute?
for i in [1, 2, 3, 3]:
print("Hello")
- A) 3
- B) 4
- C) 1
- D) Infinitely
In Python, sets are unordered collections. This means that when you create a set, the elements are stored in no particular order. Unlike lists or tuples, sets do not maintain the order of elements based on how you inserted them.
No Indexing: You cannot access elements in a set using an index like you can with lists or tuples. For example, in a list, you can access elements using indices (my_list[0]), but this is not possible in sets because there is no guaranteed order.
No Sequence: When you add elements to a set, Python may internally arrange them in an unpredictable way for efficiency. Thus, the order of elements in a set may seem random when you print or inspect the set.
my_set = {1, 2, 3, 4, 5}
# Display the set
print(my_set) # Output could be {1, 2, 3, 4, 5} or {3, 1, 4, 2, 5}
If you run the above code multiple times, you might see the elements displayed in a different order each time, but the set still contains the same unique elements.
Sets are implemented using a hash table data structure, which optimizes for operations like checking membership (in), adding, and removing elements. The elements are stored in memory based on their hash values (computed using the hash() function). This hashing process determines where the elements are placed, and their physical position in memory may not correspond to the order in which they were added.
Therefore, when you print or inspect a set, Python shows the elements in a seemingly arbitrary order, influenced by how the hash table organizes them.
my_set = {10, 20, 30, 40, 50}
# Adding new elements
my_set.add(60)
my_set.add(70)
# Display the set
print(my_set) # Output could be {40, 10, 50, 20, 70, 30, 60}
Even though 60 and 70 were added at the end, they might appear at different positions when the set is printed. This demonstrates that sets do not preserve the order of insertion.
No Guarantee of Order: Every time you perform an operation on a set or print it, you should not expect the elements to appear in the same order as you inserted them. You cannot rely on the order of elements for any kind of sequential processing.
Cannot Be Sorted Within a Set: Sets do not support sorting directly because their main property is that they are unordered. However, if you need a sorted version of a set, you can convert it to a list and then sort it.
my_set = {30, 10, 20}
sorted_list = sorted(my_set)
print(sorted_list) # Output: [10, 20, 30]
Iterating Over a Set: Even though sets are unordered, you can still iterate over them. However, the order in which you retrieve elements during iteration is not guaranteed to be the same every time.
for element in my_set:
print(element) # The order of printing is unpredictable
in and not in). Checking if an element is in a set is much faster than in lists because of the underlying hash table.Example:
my_set = {1, 2, 3, 4, 5}
# Checking if an element exists
if 3 in my_set:
print("3 is in the set")
else:
print("3 is not in the set")
Duplicate Elimination: Sets are used to quickly eliminate duplicates from collections, regardless of the order of elements. For example:
my_list = [1, 2, 2, 3, 4, 4, 5]
unique_elements = set(my_list)
print(unique_elements) # Output could be {1, 2, 3, 4, 5}
The unordered nature of sets means:
While this lack of order might seem limiting, it is also what makes sets powerful for specific tasks like ensuring uniqueness and performing fast lookups.