Top Python Interview Questions
1) What are the key features of Python?
- Easy to Learn: Python is simple and easy to read.
- Line-by-Line Execution: Makes finding errors easier.
- No Type Declarations: Python decides variable types automatically.
- Handles Complexity: Takes care of memory and other tough tasks for you.
- Built-In Tools: Has many ready-made features to help you.
- Works Everywhere: Runs on any computer system.
- Flexible Coding: Supports different ways of writing programs.
2) What is the difference between list and tuple in Python?
- Mutability:
- List: Mutable (can be modified after creation).
- Tuple: Immutable (cannot be modified after creation).
- Syntax:
- List: Defined using square brackets
[]. - Tuple: Defined using parentheses
().
- List: Defined using square brackets
- Performance:
- List: Slower for iteration and modification due to its mutability.
- Tuple: Faster because of its immutability.
Example:
# List
3) What are Python decorators, and how do they work?
Decorators are functions that modify the behavior of another function or method. They are applied using the @ symbol.
Example:
def decorator(func):
def wrapper():
print("Before function call")
func()
print("After function call")
return wrapper
@decorator
def say_hello():
print("Hello!")
say_hello()
# Output:
Before function call
Hello!
After function call
4) What is the difference between shallow copy and deep copy in Python?
- Shallow Copy: Copies the reference addresses of nested objects. Changes to nested objects affect the copied object.
- Deep Copy: Copies the actual objects recursively. Changes to nested objects do not affect the copied object.
Example:
import copy
# Shallow copy
original = [[1, 2], [3, 4]]
shallow_copied = copy.copy(original)
shallow_copied[0][0] = 5
print(original) # Output: [[5, 2], [3, 4]] (original is affected)
# Deep copy
deep_copied = copy.deepcopy(original)
deep_copied[0][0] = 9
print(original) # Output: [[5, 2], [3, 4]] (original is not affected)
5) What are Python's built-in data types?
Python's built-in data types include:
- Numeric types:
int,float,complex - Sequence types:
list,tuple,range - Text type:
str - Set types:
set,frozenset - Mapping type:
dict - Boolean type:
bool - Binary types:
bytes,bytearray,memoryview - None type:
NoneType
6) Explain the difference between is and == in Python.
is: Checks if two variables point to the same object in memory (identity comparison).==: Checks if the values of two variables are the same (value comparison).
Example:
a = [1, 2, 3]
b = [1, 2, 3]
print(a == b) # True, values are the same
print(a is b) # False, they are different objects in memory
7) What is a lambda function in Python?
A lambda function is an anonymous function defined using the lambda keyword. It can have any number of arguments but only one expression.
Example:
multiply = lambda x, y: x * y
print(multiply(2, 3)) # Output: 6
8) What are Python generators?
Generators are functions that yield items one at a time using the yield keyword. They provide an efficient way to handle large datasets without loading everything into memory at once.
Example:
def count_up_to(limit):
count = 1
while count <= limit:
yield count
count += 1
counter = count_up_to(5)
for number in counter:
print(number)
9) What are Python modules and packages?
- Module: A file containing Python code, which can define functions, classes, and variables.
- Package: A directory containing multiple modules and a special
__init__.pyfile to indicate it is a package.
Example:
mathis a built-in module.- A package might be a folder structure with multiple
.pyfiles.
10) How do you merge two dictionaries in Python?
You can merge two dictionaries using the update() method or the ** unpacking operator or in Python 3.9 and later, use the | operator
Example:
dict1 = {'a': 1, 'b': 2}
dict2 = {'b': 3, 'c': 4}
dict1.update(dict2) # Output: {'a': 1, 'b': 3, 'c': 4} OR merged_dict = {**dict1, **dict2}
print(dict1) # Output: {'a': 1, 'b': 3, 'c': 4}
OR merged = dict1 | dict2
print(merged) # Output: {'a': 1, 'b': 3, 'c': 4}11) What are Python's mutable and immutable types?
- Mutable types: Objects whose value can be changed after creation
list, dict, set- Immutable types: Objects whose value cannot be changed after creation.
tuple, str, int12) Explain the concept of slicing in Python
Slicing allows you to extract parts of a sequence (e.g., list, tuple, string) by specifying a start, stop, and step.
Example:
my_list = [0, 1, 2, 3, 4, 5] print(my_list[1:4]) # Output: [1, 2, 3] print(my_list[:3]) # Output: [0, 1, 2] print(my_list[::2]) # Output: [0, 2, 4]
13) What is the purpose of the Self keyword in Python?
The self keyword is used to refer to the instance of the class in object-oriented programming. It is used to access instance variables and methods within a class.
Example:
class MyClass:
def __init__(self, name): self.name = name def greet(self): print(f"Hello, {self.name}")
obj = MyClass("pythonbuzz")
obj.greet() # Output: Hello, pythonbuzz
14) How do you handle exceptions in Python?
Exceptions are handled using try, except, and optionally else and finally.
Example:
try:
result = 10 / 0
except ZeroDivisionError:
print("Cannot divide by zero!")
else:
print("No errors!")
finally:
print("This will always execute.")
15) What is the difference between del and remove() in Python?
del: Deletes a variable or a specific index/item from a list.remove(): Removes the first occurrence of a value from a list.
Example:
my_list = [1, 2, 3, 4] del my_list[1] # Deletes element at index 1 # Output: my_list = [1, 3, 4] my_list.remove(3) # Removes element with value 3 # Output:my_list = [1, 4]
16) What is the purpose of the with statement in Python?
The with statement is used to wrap the execution of a block of code. It simplifies exception handling and ensures resources are properly cleaned up (e.g., closing a file after use).
Example:
with open('file.txt', 'r') as file:
content = file.read()
print(content)
17) Explain Python's map() function.
The map() function applies a given function to each item of an iterable (list, tuple, etc.) and returns a map object (an iterator).
Example:
numbers = [1, 2, 3, 4]
squared = map(lambda x: x ** 2, numbers)
print(list(squared)) # Output: [1, 4, 9, 16]
18) What is list comprehension in Python?
List comprehension provides a concise way to create lists by applying an expression to each item in an iterable.
Example:
numbers = [1, 2, 3, 4]
squared = [x ** 2 for x in numbers]
print(squared) # Output: [1, 4, 9, 16]
19) What is a Python iterator and how do you create one?
An iterator is an object that lets you loop through values one at a time. To create one, you need to define two methods: __iter__() and __next__().
Example:
class MyIterator:
def __init__(self, limit):
self.limit = limit
self.current = 0
def __iter__(self):
return self
def __next__(self):
if self.current < self.limit:
self.current += 1
return self.current
else:
raise StopIteration
# Create an iterator
iterator = MyIterator(3)
# Loop through the iterator
for num in iterator:
print(num)#output:1
2
320) How does Python support object-oriented programming?
Python supports object-oriented programming (OOP) with the concepts of classes, objects, inheritance, polymorphism, encapsulation, and abstraction.
Example:
class Animal:
def __init__(self, name):
self.name = name
def speak(self):
print(f"{self.name} makes a sound")
class Dog(Animal):
def speak(self):
print(f"{self.name} barks")
dog = Dog("Buddy")
dog.speak() # Output: Buddy barks21)What are Python's data structures?
Python has the following built-in data structures:
List: Ordered, mutable, and allows duplicates.
Example: [1, 2, 3]
Tuple: Ordered, immutable, and allows duplicates.
Example: (1, 2, 3)
Set: Unordered, mutable, and does not allow duplicates.
Example: {1, 2, 3}
Dictionary: Unordered, mutable, and stores key-value pairs.
Example: {'a': 1, 'b': 2}
22)What are Python's scope rules?Python follows the LEGB rule to determine the scope of a variable:
L: Local — Variables defined inside the current function.
E: Enclosing — Variables in the enclosing function.
G: Global — Variables defined at the top level of a module.
B: Built-in — Variables provided by Python (e.g., print, len).
Example: x = 10 # Global scope
def outer():
y = 5 # Enclosing scope
def inner():
z = 2 # Local scope
print(x, y, z)
inner()
outer()23)What is the difference between args and kwargs in Python?*args: Allows a function to accept a variable number of positional arguments.
**kwargs: Allows a function to accept a variable number of keyword arguments.
Example: def demo_function(*args, **kwargs):
print("Positional arguments:", args)
print("Keyword arguments:", kwargs)
demo_function(1, 2, 3, name="Alice", age=30)
# Output:
# Positional arguments: (1, 2, 3)
# Keyword arguments: {'name': 'Alice', 'age': 30}24)What is the purpose of Python's zip() function?The zip() function combines multiple iterables into tuples, creating a single iterator.
Example:
names = ['Rama', 'Sita']
age = [30, 25]
zipped = zip(names, age)
print(list(zipped))
# Output: [('Rama', 30), ('Sita', 25)]
25)Explain Python's enumerate() function.
The enumerate() function adds a counter to an iterable and returns it as an
enumerate object.
Example:
names = ['Alice', 'Bob']
for index, name in enumerate(names):
print(index, name)
# Output:
0 Alice
1 Bob
26)What are Python's memory management features?
Garbage Collection: Python automatically manages memory using reference
counting and a cyclic garbage collector.
Dynamic Memory Allocation: Objects are stored in a private heap managed
by Python.
del Keyword: Used to delete references to an object.
Example: import gc
x = [1, 2, 3]
del x
gc.collect() # Triggers garbage collection27)What is the difference between compile-time and runtime errors in Python?Compile-time errors: Occur when there is an issue in the syntax.
Example: print("Hello # Missing closing quote.
Runtime errors: Occur while the program is running.
Example: Division by zero: 10 / 0
28)What are Python's magic methods?Magic methods (or dunder methods) are special methods with double underscores
that enable operator overloading and customization.
Example:
class MyClass:
def __init__(self, value):
self.value = value
def __add__(self, other):
return self.value + other.value
obj1 = MyClass(10)
obj2 = MyClass(20)
print(obj1 + obj2) # Output: 30
29)What is the purpose of Python's all() and any() functions?
all(): Returns True if all elements in an iterable are true.
any(): Returns True if at least one element in an iterable is true.
Example: nums = [1, 2, 0]
print(all(nums)) # Output: False
print(any(nums)) # Output: True30)What is Python's pass statement?The pass statement is a placeholder used when a statement is syntactically required
but no action is needed.
Example:
def my_function():
pass
31)How do you check the type of a variable in Python?
Use the type() function to check the type of a variable.
Example:
x = 42
print(type(x)) # Output: <class 'int'>
32)What are Python's membership operators?Membership operators (in, not in) test for membership in a sequence
(like a list or string).
Example:
my_list = [1, 2, 3]
print(2 in my_list) # Output: True
print(4 not in my_list) # Output: True
33) How do you reverse a list in Python?
You can use slicing, the reversed() function, or the .reverse() method.
Example: my_list = [1, 2, 3]
print(my_list[::-1]) # Output: [3, 2, 1]
print(list(reversed(my_list))) # Output: [3, 2, 1]
my_list.reverse() print(my_list) # Output: [3, 2, 1]
34)What are Python's logical operators?Python has three logical operators: and, or, and not.
Example:
a = True
b = False
print(a and b) # Output: False
print(a or b) # Output: True
print(not a) # Output: False
35) How do you concatenate strings in Python?You can concatenate strings using the + operator or the join() method.
Example:
str1 = "Hello"
str2 = "World"
print(str1 + " " + str2) # Output: Hello World
print(" ".join([str1, str2])) # Output: Hello World
36)What is the difference between break, continue, and pass?- break: Exits the loop completely.
- continue: Skips the current iteration and moves to the next one.
- pass: Does nothing, just a placeholder.
Example:
for i in range(5):
if i == 2:
break # Exits loop when i is 2
print(i)
for i in range(5):
if i == 2:
continue # Skips when i is 2
print(i)
for i in range(5):
if i == 2:
pass # Does nothing
print(i)
37)How do you handle a file not found error in Python?Use a try block with exception handling.
Example:
try:
with open('non_existent_file.txt', 'r') as file:
content = file.read()
except FileNotFoundError:
print("File not found!")
38)How do you sort a list of dictionaries by a key?Use the sorted() function with a key parameter.
Example:
data = [{'name': 'John', 'age': 25}, {'name': 'Alice', 'age': 22}]
sorted_data = sorted(data, key=lambda x: x['age'])
print(sorted_data)
# Output:
[{'name': 'Alice', 'age': 22}, {'name': 'John', 'age': 25}]
39)What is the __name__ == "__main__" construct in Python?This ensures a script runs only when executed directly, not when imported as a module.
Example:
if __name__ == "__main__":
print("This runs only when the script is executed directly.")
40)How do you count occurrences of elements in a list?Use the Counter class from the collections module.
Example:
from collections import Counter
my_list = [1, 2, 2, 3, 3, 3]
print(Counter(my_list))
# Output: Counter({3: 3, 2: 2, 1: 1})
41)What are Python's set operations?Sets support operations like union, intersection, difference, and symmetric difference.
Example:
set1 = {1, 2, 3}
set2 = {3, 4, 5}
print(set1 | set2) # Union: {1, 2, 3, 4, 5}
print(set1 & set2) # Intersection: {3}
print(set1 - set2) # Difference: {1, 2}
print(set1 ^ set2) # Symmetric Difference: {1, 2, 4, 5}
42)What is the eval() function in Python?The eval() function evaluates a string expression as Python code.
Example:
x = 5
expression = 'x * 2'
print(eval(expression)) # Output: 10
43)How can you reverse a string in Python?Using slicing or the reversed() function.
Example:
# Using slicing
string = "Python"
reversed_string = string[::-1]
print(reversed_string) # Output: nohtyP
# Using reversed()
print(''.join(reversed(string))) # Output: nohtyP
44)What are Python's comprehensions, and why are they used?Comprehensions provide a concise way to create lists, sets, and dictionaries.
Examples:
# List comprehension
squares = [x**2 for x in range(5)]
# Set comprehension
unique = {x for x in 'hello'}
# Dictionary comprehension
squared_dict = {x: x**2 for x in range(5)}
45)What is the difference between mutable and immutable types in Python?- Mutable: Can be modified after creation (e.g.,
list, dict, set). - Immutable: Cannot be modified after creation (e.g.,
int, float, str, tuple).
Example:
mutable = [1, 2, 3]
mutable[0] = 99
print(mutable) # [99, 2, 3]
immutable = "hello"
immutable[0] = 'H' # Error: 'str' object does not support item assignment
46)How do you open a file in Python? What are the different modes for opening a file?The open() function is used to open a file in Python. It takes two arguments:
- The file name.
- The mode in which the file is opened.
Common modes are:
r: Read (default mode, file must exist).w: Write (creates a new file or overwrites an existing file).a: Append (adds data to the end of the file).rb, wb, ab: Same as above, but for binary files.
Example:
47)What is the difference between read(), readline(), and readlines()?read(): Reads the entire file as a string.readline(): Reads one line from the file.readlines(): Reads all lines as a list of strings.
Example:
# Writing content to the file
with open("example.txt", "w") as file:
file.write("First line\nSecond line\nThird line")
# Reading the file
with open("example.txt", "r") as file:
print(file.read()) # Reads entire file
file.seek(0) # Reset cursor to start
print(file.readline()) # Reads the first line
print(file.readlines()) # Reads all lines as a list
48)What is the difference between w and a modes in file handling?w: Overwrites the file if it exists or creates a new file.a: Appends to the file if it exists or creates a new file.
Example:
# Using 'w' mode
with open("example.txt", "w") as file:
file.write("This overwrites the file.")
# Using 'a' mode
with open("example.txt", "a") as file:
file.write("\nThis appends to the file.")
import and from ... import?import: Imports the entire module, and you access its contents using the module name.from ... import: Imports specific functions, classes, or variables from a module.
Example:
# Import the entire module
import math
print(math.sqrt(16)) # Output: 4.0
# Import only specific function
from math import sqrt
print(sqrt(16)) # Output: 4.0
- A module is a single Python file.
- A package is a collection of modules organized in a directory with an
__init__.pyfile.
Example:
Directory structure for a package named my_package:
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