Python Interview Questions and Answers
This is a comprehensive list of over 30 interview questions and detailed answers for Python, covering a range of topics from fundamental concepts to advanced techniques and best practices.
This is a comprehensive list of over 30 interview questions and detailed answers for Python, covering a range of topics from fundamental concepts to advanced techniques and best practices.
Section 1: Python Fundamentals and Syntax
1.What is Python?
Answer: Python is a high-level, interpreted, object-oriented, and general-purpose programming language. It is known for its simple, readable syntax, which makes it an excellent language for beginners and for developing a wide range of applications, from web development and data science to machine learning and automation.
2.Explain the difference between lists and tuples.
Answer:
Explain the difference between lists and tuples.Lists are mutable, meaning their elements can be changed, added, or removed after creation. They are defined with square brackets [].
Tuples are immutable, meaning their elements cannot be changed once they are created. They are defined with parentheses (). Tuples are generally faster and more memory-efficient than lists and are used when the data is not intended to be changed.
3.What are Python decorators? Provide an example.
Answer: A decorator is a function that takes another function as an argument, adds some functionality, and returns another function without altering the source code of the original function. They are typically used for logging, access control, or timing the execution of functions.
def my_decorator(func):
def wrapper():
print(“Something is happening before the function is called.”)
func()
print(“Something is happening after the function is called.”)
return wrapper
@my_decorator
def say_hello():
print(“Hello!”)
say_hello()
4.What is a dictionary in Python?
Answer: A dictionary is an unordered, mutable collection of key-value pairs. Dictionaries are optimized for retrieving values when the key is known. They are defined with curly braces {} and each key-value pair is separated by a colon, like {‘name’: ‘Alice’, ‘age’: 30}.
5.What is the Global Interpreter Lock (GIL)?
Answer: The GIL is a mutex (lock) that protects access to Python objects, preventing multiple native threads from executing Python bytecodes at the same time. This means that even on a multi-core processor, only one thread can execute Python code at any given time. The GIL can be a performance bottleneck for CPU-bound tasks, but it is less of an issue for I/O-bound tasks.
6.What are the key differences between range(), xrange(), and
enumerate()?
Answer:
range(): Returns a list of numbers. It is an in-memory function, so it can be slow and memory-intensive for very large ranges.
xrange() (Python 2): A generator that returns an iterator object, yielding one number at a time. It was more memory-efficient than range(). (Note: xrange was removed in Python 3, and range() now behaves like xrange.)
enumerate(): A built-in function that adds a counter to an iterable and returns it as an enumerate object. It is a more Pythonic way to loop through a list and access both the index and the item.
7.How are arguments passed in Python?
Answer: In Python, arguments are passed by “assignment,” which can be thought of as a mix of pass-by-value and pass-by-reference. When you pass a mutable object (like a list), the function gets a reference to that object, so changes made inside the function will affect the original object. When you pass an immutable object (like an integer or string), the function gets a copy of the value, and changes do not affect the original.
8.What is self in Python?
Answer: self is the first parameter of a method within a class. It refers to the instance of the object itself. It is a convention, not a keyword, but it is a required part of method definitions to allow access to the object’s attributes and methods.
9.What Is _init_ Function in Python?
Answer:__init__ (the constructor): This is a special method that is automatically called when a new instance of a class is created. It is used to initialize the object’s attributes.__str__ (the string representation): This method returns a human-readable string representation of an object. It is called by functions like print() and str().
10.What is Inheritance in Python?
Answer: Inheritance is an OOP concept where a class (the “child” or “subclass”) derives the attributes and methods of another class (the “parent” or “superclass”). This promotes code reusability and establishes an “is-a” relationship between classes.
11.What is method overriding?
Answer: Method overriding is a feature where a subclass provides a specific implementation of a method that is already defined in its superclass. This allows a child class to have a method with the same name and parameters as the parent class, but with different behavior.
12.What is polymorphism?
Answer: Polymorphism is an OOP principle that allows objects of different classes to be treated as objects of a common superclass. This means that a single function can operate on objects of different types, and the method called will depend on the type of the object at runtime.
Section 3: Data Structures and Comprehensions
13.What is a list comprehension? Provide an example.
Answer: List comprehensions are a concise way to create lists in a single line. They consist of an expression followed by a for clause, and optionally if clauses. They are generally faster and more readable than traditional loops for creating lists.
squares = [x**2 for x in range(10)]
# Result: [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
14.What are sets in Python?
Answer: A set is an unordered collection of unique elements. Sets are mutable but do not allow duplicate values. They are useful for performing mathematical set operations like union, intersection, difference, and for quickly checking if an element is in the set.
15.Explain how a dictionary stores data internally.
Answer: A dictionary uses a hash table data structure. When you create a key-value pair, Python computes a hash value for the key and uses that value to find an address in the hash table where the key and its corresponding value will be stored. This allows for very fast lookup times.
16.What is a generator in Python?
Answer: A generator is a special type of function that returns an iterator. Instead of returning a value and terminating, a generator “yields” a value. This allows the function to pause its execution and save its state, so it can resume from where it left off later. Generators are highly memory-efficient for processing large data streams because they generate values on-demand.
Section 4: Common Libraries and Modules
17.What is pip?
Answer: pip (Preferred Installer Program) is the standard package manager for Python. It is used to install, uninstall, and manage Python packages and libraries from the Python Package Index (PyPI).
18.How do you handle exceptions in Python?
Answer: Exceptions are handled using try, except, else, and finally blocks.
The try block contains the code that might raise an exception.
The except block catches a specific type of exception and handles it.
The else block runs if the try block completes without an exception.
The finally block always executes, regardless of whether an exception occurred.
19.What is pandas and what is it used for?
Answer: pandas is a fast, powerful, flexible, and easy-to-use open-source data analysis and manipulation library. It is widely used in data science and machine learning for working with structured data, such as CSV files, spreadsheets, and SQL tables. Its two main data structures are the Series and the DataFrame.
20.What is the purpose of the numpy library?
Answer: numpy is a fundamental package for scientific computing with Python. It provides support for large, multi-dimensional arrays and matrices, along with a collection of mathematical functions to operate on these arrays. It is significantly more efficient than standard Python lists for numerical operations.
Section 5: Advanced Topics and Best Practices
21.What is the difference between == and is?
Answer:== checks for equality of value. It returns True if the objects being compared have the same value.
is checks for object identity. It returns True if two variables point to the exact same object in memory.
22.What is a virtual environment in Python?
Answer: A virtual environment is a self-contained directory that holds a specific Python interpreter and its own set of installed packages. It allows developers to work on multiple projects with different dependencies without conflicts.
23.What is the purpose of __name__ == ‘__main__’?
Answer: __name__ is a built-in variable that is set to __main__ when the script is executed directly. This conditional block ensures that the code inside it only runs when the file is executed as the main program, and not when it’s imported as a module into another script.
24.What are mutable and immutable objects?
Answer:Mutable objects can be changed after they are created. Examples include lists, dictionaries, and sets.
Immutable objects cannot be changed after they are created. Examples include integers, floats, strings, and tuples.
25.What is a closure in Python?
Answer: A closure is a function object that remembers values from its enclosing scope, even if that scope no longer exists. A closure is formed when a nested function references a variable from its outer scope.
26.Explain the concept of a lambda function.
Answer: A lambda function is a small, anonymous function that can have any number of arguments but can only have one expression. They are typically used for simple, one-off operations where defining a full function with def is unnecessary.
27.What is a “context .
Answer: A context manager is an object that defines the runtime context for a block of code. The with statement is a control flow structure that automatically handles the setup and teardown of resources. For example, with open(‘file.txt’, ‘r’) as f: ensures that the file is automatically closed after the block is executed.
28.How do you perform unit testing in Python?
Answer: Python has a built-in unittest module for creating and running test cases. Other popular testing frameworks include pytest, which is known for its simplicity and powerful features.
29.What is serialization and deserialization?
Answer: Serialization (or “pickling”) is the process of converting a Python object into a stream of bytes so it can be stored in a file, database, or transmitted over a network.
Deserialization (or “unpickling”) is the reverse process: converting the stream of bytes back into a Python object. Python’s pickle module is commonly used for this.
30.What is a docstring?
Answer: A docstring is a string literal that appears as the first statement in a module, function, class, or method definition. It is used to provide documentation for the code and can be accessed at runtime using the __doc__ attribute.
31.What is the difference between an iterator and an iterable?
Answer:An iterable is an object that can be looped over (e.g., lists, strings, dictionaries). It has an __iter__ method that returns an iterator.
An iterator is an object that represents a stream of data. It has a __next__ method that returns the next item in the stream and raises a StopIteration exception when all items have been returned.
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