Python Interview Questions and Answers
Practice every question in this topic using expandable answers and interview tips. Answer aloud first, then open the explanation.
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Q1. What is Python? [Easy]
Answer: Python is a high-level, interpreted, object-oriented, and general-purpose programming language created by Guido van Rossum. It is known for its simple syntax, readability, and extensive standard library. Python is widely used in web development, data science, artificial intelligence, automation, scripting, cybersecurity, and desktop application development.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q2. What are the main features of Python? [Easy]
Answer: Python is easy to learn, interpreted, dynamically typed, object-oriented, cross-platform, open source, supports multiple programming paradigms, has automatic memory management, and provides a rich ecosystem of libraries and frameworks.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q3. What are the advantages of using Python? [Easy]
Answer: Python offers clean and readable syntax, rapid application development, a large standard library, excellent community support, cross-platform compatibility, automatic garbage collection, and libraries for almost every domain including AI, web development, automation, and data analysis.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q4. What is the difference between Python 2 and Python 3? [Medium]
Answer: Python 3 is the modern version and is actively maintained. It improves Unicode support, uses print() as a function, provides better integer division behavior, and includes many performance and language improvements. Python 2 reached end-of-life and is no longer supported.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q5. What are variables in Python? [Easy]
Answer: Variables are names that reference objects stored in memory. Python is dynamically typed, so variables do not require explicit type declarations. A variable's type is determined automatically based on the assigned value.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q6. What are identifiers in Python? [Medium]
Answer: Identifiers are names used for variables, functions, classes, modules, and other objects. They can contain letters, digits, and underscores but cannot start with a digit or use Python reserved keywords.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q7. What are keywords in Python? [Easy]
Answer: Keywords are reserved words that have predefined meanings in Python and cannot be used as identifiers. Examples include if, else, for, while, class, def, return, try, except, import, and lambda.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q8. What is the difference between interpreted and compiled languages? [Medium]
Answer: Compiled languages convert the entire source code into machine code before execution. Interpreted languages execute code line by line using an interpreter. Python is primarily interpreted, although it first compiles source code into bytecode before execution by the Python Virtual Machine (PVM).
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q9. What is PEP 8? [Medium]
Answer: PEP 8 is the official Python style guide. It defines coding standards such as naming conventions, indentation, line length, spacing, imports, and formatting to improve code readability and maintainability.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q10. What is the Python Virtual Machine (PVM)? [Hard]
Answer: The Python Virtual Machine (PVM) is the runtime engine that executes Python bytecode. When a Python program runs, the source code is first compiled into bytecode (.pyc files), and the PVM interprets this bytecode to execute the program. This design makes Python portable across different operating systems.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q11. What are the built-in data types in Python? [Easy]
Answer: Python provides several built-in data types, including numeric types (int, float, complex), text (str), sequence types (list, tuple, range), mapping type (dict), set types (set, frozenset), boolean (bool), binary types (bytes, bytearray, memoryview), and NoneType.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q12. What is the difference between int, float, and complex data types? [Easy]
Answer: The int type stores whole numbers, float stores decimal numbers, and complex stores numbers with real and imaginary parts, such as 3 + 4j.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q13. What is a string in Python? [Medium]
Answer: A string is an immutable sequence of Unicode characters enclosed in single quotes, double quotes, or triple quotes. Strings support slicing, indexing, formatting, and numerous built-in methods for text processing.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q14. What is the difference between a list and a tuple? [Medium]
Answer: Lists are mutable, allowing elements to be added, removed, or modified after creation. Tuples are immutable, making them faster and suitable for storing fixed collections of data that should not change.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q15. What is a set in Python? [Medium]
Answer: A set is an unordered collection of unique elements. It automatically removes duplicate values and supports efficient operations such as union, intersection, difference, and membership testing.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q16. What is a dictionary in Python? [Medium]
Answer: A dictionary is a mutable collection of key-value pairs. Each key must be unique, and values can be of any data type. Dictionaries provide fast lookup, insertion, and deletion operations using keys.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q17. What is the difference between mutable and immutable objects in Python? [Hard]
Answer: Mutable objects can be modified after they are created, while immutable objects cannot. Lists, dictionaries, and sets are mutable. Strings, tuples, integers, floats, booleans, and frozensets are immutable. Understanding mutability is important for memory management and function behavior.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q18. What is type conversion in Python? [Medium]
Answer: Type conversion is the process of converting one data type into another. Python supports implicit conversion performed automatically and explicit conversion using functions such as int(), float(), str(), list(), tuple(), set(), and dict().
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q19. What are the different types of operators in Python? [Medium]
Answer: Python supports arithmetic, comparison, assignment, logical, bitwise, identity, membership, and conditional (ternary) operators. These operators are used to perform calculations, comparisons, assignments, and logical operations.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q20. What is the difference between the '==' operator and the 'is' operator in Python? [Hard]
Answer: The '==' operator compares whether two objects have the same value, while the 'is' operator compares whether two variables reference the exact same object in memory. Use '==' for value comparison and 'is' when checking object identity, such as comparing with None.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q21. What is a function in Python? [Easy]
Answer: A function is a reusable block of code that performs a specific task. Functions help reduce code duplication, improve readability, and make programs easier to maintain. Functions are defined using the def keyword and can accept parameters and return values.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q22. What are the different types of function arguments in Python? [Medium]
Answer: Python supports positional arguments, keyword arguments, default arguments, and variable-length arguments. Variable-length arguments include *args for multiple positional arguments and **kwargs for multiple keyword arguments.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q23. What are *args and **kwargs in Python? [Hard]
Answer: *args allows a function to accept any number of positional arguments as a tuple. **kwargs allows a function to accept any number of keyword arguments as a dictionary. They make functions flexible and reusable when the number of inputs is unknown.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q24. What is a lambda function in Python? [Medium]
Answer: A lambda function is an anonymous function defined using the lambda keyword. It is typically used for short expressions and is commonly passed to functions such as map(), filter(), sorted(), and reduce().
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q25. What is recursion in Python? [Medium]
Answer: Recursion is a programming technique where a function calls itself to solve a problem. Every recursive function must have a base case to stop further recursive calls and prevent infinite recursion.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q26. What are modules in Python? [Easy]
Answer: A module is a Python file containing functions, classes, variables, and executable code. Modules help organize code into reusable units and can be imported into other Python programs using the import statement.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q27. What is the difference between a module and a package? [Medium]
Answer: A module is a single Python (.py) file containing Python code. A package is a collection of related modules organized into directories. Packages help organize large applications into manageable components.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q28. What is Object-Oriented Programming (OOP)? [Medium]
Answer: Object-Oriented Programming (OOP) is a programming paradigm that organizes code into objects containing data and methods. OOP improves code reusability, modularity, maintainability, and scalability through concepts such as inheritance, encapsulation, abstraction, and polymorphism.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q29. What are classes and objects in Python? [Medium]
Answer: A class is a blueprint used to create objects. It defines the attributes and methods that objects will have. An object is an instance of a class that contains actual data and can invoke the methods defined in the class.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q30. Explain the four pillars of Object-Oriented Programming. [Hard]
Answer: The four pillars of OOP are Encapsulation, which protects data by combining it with methods; Inheritance, which allows one class to acquire the properties and behavior of another; Polymorphism, which allows the same interface to have multiple implementations; and Abstraction, which hides implementation details while exposing only essential functionality.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q31. What is exception handling in Python? [Medium]
Answer: Exception handling is the process of detecting and handling runtime errors without terminating the program. Python uses try, except, else, and finally blocks to manage exceptions and ensure the application continues to run gracefully.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q32. What is the purpose of try, except, else, and finally blocks? [Easy]
Answer: The try block contains code that may raise an exception. The except block handles the exception. The else block executes if no exception occurs, and the finally block always executes regardless of whether an exception was raised, making it ideal for resource cleanup.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q33. How do you raise a custom exception in Python? [Medium]
Answer: A custom exception can be raised using the raise keyword. Developers can also create custom exception classes by inheriting from the built-in Exception class to represent application-specific errors.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q34. What is file handling in Python? [Medium]
Answer: File handling is the process of creating, opening, reading, writing, appending, and closing files. Python provides the built-in open() function and supports multiple file modes such as 'r', 'w', 'a', 'x', and 'b'.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q35. What are the different file modes available in Python? [Medium]
Answer: Common file modes include 'r' (read), 'w' (write), 'a' (append), 'x' (create), 'rb' (read binary), 'wb' (write binary), 'r+' (read and write), and 'a+' (append and read).
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q36. Why is the with statement used while working with files? [Medium]
Answer: The with statement automatically manages resources by opening and closing files safely. It ensures that the file is properly closed even if an exception occurs, eliminating the need to explicitly call close().
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q37. What is the difference between an iterator and an iterable? [Hard]
Answer: An iterable is any object that can return an iterator using the iter() function, such as lists, tuples, and strings. An iterator is an object that implements the __iter__() and __next__() methods to return one item at a time until a StopIteration exception is raised.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q38. What is the purpose of the enumerate() function? [Medium]
Answer: The enumerate() function returns both the index and value while iterating over a sequence. It simplifies loops by eliminating the need to manually maintain a counter.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q39. What is the zip() function in Python? [Medium]
Answer: The zip() function combines multiple iterables into a single iterator of tuples by pairing elements with the same index. It is commonly used to iterate over multiple sequences simultaneously.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q40. What is the difference between shallow copy and deep copy? [Hard]
Answer: A shallow copy creates a new object but shares references to nested objects with the original. A deep copy recursively copies all nested objects, creating a completely independent duplicate. Python provides the copy.copy() and copy.deepcopy() functions for these operations.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q41. What is a list comprehension in Python? [Medium]
Answer: A list comprehension is a concise way to create lists using a single expression. It combines looping and conditional logic into one readable statement, making the code shorter and often faster than traditional loops.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q42. What is a dictionary comprehension? [Medium]
Answer: A dictionary comprehension provides a compact way to create dictionaries using a single expression. It allows keys and values to be generated dynamically while iterating over another iterable.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q43. What is a generator in Python? [Hard]
Answer: A generator is a special type of iterator that produces values one at a time instead of storing all values in memory. Generators are memory-efficient and are especially useful when working with large datasets or infinite sequences.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q44. What is the yield keyword in Python? [Hard]
Answer: The yield keyword is used inside a generator function to return one value at a time while preserving the function's execution state. Unlike return, yield pauses the function and resumes execution when the next value is requested.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q45. What is the difference between return and yield? [Hard]
Answer: The return statement immediately terminates a function and returns a value. The yield statement pauses execution, returns a value, and allows the function to resume later, making it suitable for generators and lazy evaluation.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q46. What is a decorator in Python? [Hard]
Answer: A decorator is a function that adds or modifies the behavior of another function or method without changing its source code. Decorators are commonly used for logging, authentication, authorization, caching, validation, and performance measurement.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q47. What is a closure in Python? [Hard]
Answer: A closure is a nested function that remembers and can access variables from its enclosing scope even after the outer function has finished executing. Closures are commonly used to preserve state and implement decorators.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q48. What is a context manager in Python? [Hard]
Answer: A context manager is an object that automatically manages resources such as files, database connections, and network sockets. It is commonly used with the with statement to ensure resources are properly acquired and released, even if an exception occurs.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q49. What is the collections module in Python? [Medium]
Answer: The collections module provides specialized container data types that extend Python's built-in containers. Popular classes include Counter, defaultdict, OrderedDict, deque, ChainMap, and namedtuple.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q50. What are namedtuple and defaultdict in Python? [Hard]
Answer: namedtuple creates lightweight tuple subclasses with named fields, making code more readable. defaultdict is a dictionary subclass that automatically provides a default value for missing keys, eliminating the need to check whether a key exists before accessing it.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q51. What is multithreading in Python? [Hard]
Answer: Multithreading is a technique that allows multiple threads to run concurrently within a single process. It is best suited for I/O-bound tasks such as file operations, network requests, and database access. Python provides the threading module to create and manage threads.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q52. What is multiprocessing in Python? [Hard]
Answer: Multiprocessing allows a program to execute multiple processes simultaneously. Each process has its own memory space and Python interpreter, making it ideal for CPU-intensive tasks. The multiprocessing module enables applications to fully utilize multiple CPU cores.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q53. What is the Global Interpreter Lock (GIL)? [Hard]
Answer: The Global Interpreter Lock (GIL) is a mechanism in CPython that allows only one thread to execute Python bytecode at a time. While it simplifies memory management, it limits true parallel execution of CPU-bound threads. It has less impact on I/O-bound applications because threads release the GIL during many blocking I/O operations.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q54. What is asyncio in Python? [Hard]
Answer: asyncio is Python's built-in library for asynchronous programming. It uses an event loop along with async and await keywords to execute multiple I/O-bound operations concurrently without creating multiple threads.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q55. What is the difference between multithreading, multiprocessing, and asyncio? [Hard]
Answer: Multithreading is best for I/O-bound tasks but is limited by the GIL for CPU-bound work. Multiprocessing creates separate processes that can run truly in parallel, making it suitable for CPU-intensive tasks. asyncio uses a single-threaded event loop to efficiently handle many asynchronous I/O operations without creating additional threads or processes.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q56. What is thread safety? [Medium]
Answer: Thread safety ensures that shared data remains consistent when accessed by multiple threads simultaneously. It is achieved using synchronization mechanisms such as locks, semaphores, and thread-safe data structures.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q57. What are Lock, RLock, Semaphore, and Event in Python? [Hard]
Answer: Lock provides mutual exclusion by allowing only one thread to access a shared resource at a time. RLock (Reentrant Lock) allows the same thread to acquire the lock multiple times. Semaphore limits the number of threads accessing a resource simultaneously. Event enables one thread to signal one or more waiting threads when a specific condition occurs.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q58. What is a Queue in Python? [Medium]
Answer: A Queue is a thread-safe data structure used for safely exchanging data between threads or processes. The queue module provides FIFO, LIFO, and Priority Queue implementations for concurrent programming.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q59. How do processes communicate in Python? [Hard]
Answer: Processes can communicate using multiprocessing.Queue, Pipe, shared memory, Value, Array, or synchronization primitives provided by the multiprocessing module. These mechanisms enable safe data exchange between independent processes.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q60. What are the best practices for concurrent programming in Python? [Hard]
Answer: Choose multithreading for I/O-bound tasks, multiprocessing for CPU-bound tasks, and asyncio for high-concurrency asynchronous applications. Minimize shared mutable state, use synchronization primitives when needed, avoid deadlocks, use thread-safe queues for communication, handle exceptions properly, and profile your application before optimizing concurrency.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q61. What is a virtual environment in Python? [Easy]
Answer: A virtual environment is an isolated Python environment that allows each project to have its own Python interpreter, packages, and dependencies. It helps avoid version conflicts between different projects and is commonly created using the built-in venv module.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q62. What is pip in Python? [Easy]
Answer: pip is Python's default package manager. It is used to install, upgrade, remove, and manage third-party packages from the Python Package Index (PyPI) or other package repositories.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q63. What is SQLite and when should it be used? [Medium]
Answer: SQLite is a lightweight, serverless relational database that stores the entire database in a single file. It is ideal for small applications, desktop software, mobile apps, prototypes, and local development environments.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q64. How do you connect Python to MySQL or PostgreSQL? [Medium]
Answer: Python connects to relational databases using database drivers such as mysql-connector-python, PyMySQL, or psycopg2. Developers can also use ORMs like SQLAlchemy or Django ORM to simplify database interactions and reduce boilerplate SQL code.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q65. What is Flask? [Medium]
Answer: Flask is a lightweight Python web framework used for building web applications and REST APIs. It provides routing, request handling, template rendering, and extension support while giving developers flexibility in choosing project components.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q66. What is Django? [Medium]
Answer: Django is a high-level Python web framework that follows the Model-View-Template (MVT) architecture. It includes built-in features such as an ORM, authentication, an admin interface, form handling, security protections, and URL routing, enabling rapid web application development.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q67. What is the difference between Django and Flask? [Hard]
Answer: Django is a full-featured framework with built-in authentication, ORM, admin panel, form handling, and security features, making it suitable for large applications. Flask is lightweight and minimal, allowing developers to choose only the libraries they need, making it ideal for microservices, APIs, and smaller applications.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q68. What is a REST API? [Medium]
Answer: A REST API is a web service that follows REST architectural principles and communicates using HTTP methods such as GET, POST, PUT, PATCH, and DELETE. REST APIs commonly exchange data in JSON format and are widely used for communication between clients and servers.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q69. What is FastAPI and why is it popular? [Hard]
Answer: FastAPI is a modern Python web framework designed for building high-performance APIs. It supports asynchronous programming, automatic request validation using type hints, automatic OpenAPI and Swagger documentation generation, and excellent performance comparable to Node.js and Go for many API workloads.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q70. What is SQLAlchemy? [Hard]
Answer: SQLAlchemy is a powerful Python SQL toolkit and Object-Relational Mapper (ORM). It allows developers to interact with relational databases using Python objects while also supporting raw SQL queries, transactions, connection pooling, and database migrations through related tools.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q71. How is memory managed in Python? [Hard]
Answer: Python automatically manages memory using private memory spaces, reference counting, and a garbage collector. Objects are created on the heap, and memory is automatically reclaimed when objects are no longer referenced, reducing the need for manual memory management.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q72. What is garbage collection in Python? [Hard]
Answer: Garbage collection is the process of automatically identifying and removing objects that are no longer in use. Python combines reference counting with a cyclic garbage collector to detect and clean up circular references that reference counting alone cannot remove.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q73. What is reference counting in Python? [Hard]
Answer: Reference counting is the primary memory management technique used by CPython. Every object keeps track of how many references point to it. When the reference count reaches zero, the object's memory is released automatically unless it is part of a reference cycle handled by the garbage collector.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q74. What is the purpose of if __name__ == "__main__"? [Medium]
Answer: The special variable __name__ is set to '__main__' when a Python file is executed directly. The condition if __name__ == '__main__': ensures that specific code runs only when the file is executed as the main program and not when it is imported as a module.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q75. What is __slots__ in Python? [Hard]
Answer: __slots__ is a class attribute that restricts the set of attributes instances can have. It reduces memory usage and can improve attribute access performance by preventing the creation of an instance __dict__ when dynamic attributes are not needed.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q76. What is the difference between __str__() and __repr__()? [Medium]
Answer: __str__() returns a user-friendly string representation of an object, while __repr__() returns an unambiguous representation intended for developers and debugging. If __str__() is not implemented, Python falls back to using __repr__().
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q77. How can you improve the performance of a Python application? [Hard]
Answer: Performance can be improved by choosing efficient algorithms and data structures, using generators for large datasets, minimizing unnecessary object creation, leveraging built-in functions, optimizing database queries, using caching, profiling code to identify bottlenecks, and using multiprocessing or asynchronous programming when appropriate.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q78. What tools are used for profiling Python applications? [Hard]
Answer: Common profiling tools include cProfile, profile, timeit, memory_profiler, tracemalloc, line_profiler, and py-spy. These tools help identify CPU, memory, and performance bottlenecks in Python applications.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q79. What are Python coding best practices? [Hard]
Answer: Follow PEP 8 guidelines, write readable and modular code, use meaningful variable names, avoid global variables, handle exceptions appropriately, write unit tests, document code with docstrings, use virtual environments, manage dependencies carefully, and keep functions small and focused on a single responsibility.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Q80. What are common Python interview mistakes and how can they be avoided? [Hard]
Answer: Common mistakes include confusing 'is' with '==', using mutable objects as default function arguments, ignoring exception handling, writing inefficient loops instead of using built-in functions or comprehensions, misunderstanding variable scope, and neglecting time and space complexity. Understanding core Python concepts and practicing coding problems regularly helps avoid these mistakes.
Interview tip: Define it clearly, give a small example, and mention one practical use or limitation.
Study checklist
- Explain the answer without reading.
- Write one small example.
- Compare framework or database version differences in official documentation.
Python Interview Questions and Answers
Practice one question at a time. Read the question, answer aloud, then compare your explanation with the answer.
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Q1. What is Python?
Easy
Answer: Python is a high-level, interpreted, object-oriented, and general-purpose programming language created by Guido van Rossum. It is known for its simple syntax, readability, and extensive standard library. Python is widely used in web development, data science, artificial intelligence, automation, scripting, cybersecurity, and desktop application development.
Interview tip: Use a short example and connect the answer to real project work.
Q2. What are the main features of Python?
Easy
Answer: Python is easy to learn, interpreted, dynamically typed, object-oriented, cross-platform, open source, supports multiple programming paradigms, has automatic memory management, and provides a rich ecosystem of libraries and frameworks.
Interview tip: Use a short example and connect the answer to real project work.
Q3. What are the advantages of using Python?
Easy
Answer: Python offers clean and readable syntax, rapid application development, a large standard library, excellent community support, cross-platform compatibility, automatic garbage collection, and libraries for almost every domain including AI, web development, automation, and data analysis.
Interview tip: Use a short example and connect the answer to real project work.
Q4. What is the difference between Python 2 and Python 3?
Medium
Answer: Python 3 is the modern version and is actively maintained. It improves Unicode support, uses print() as a function, provides better integer division behavior, and includes many performance and language improvements. Python 2 reached end-of-life and is no longer supported.
Interview tip: Use a short example and connect the answer to real project work.
Q5. What are variables in Python?
Easy
Answer: Variables are names that reference objects stored in memory. Python is dynamically typed, so variables do not require explicit type declarations. A variable's type is determined automatically based on the assigned value.
Interview tip: Use a short example and connect the answer to real project work.
Q6. What are identifiers in Python?
Medium
Answer: Identifiers are names used for variables, functions, classes, modules, and other objects. They can contain letters, digits, and underscores but cannot start with a digit or use Python reserved keywords.
Interview tip: Use a short example and connect the answer to real project work.
Q7. What are keywords in Python?
Easy
Answer: Keywords are reserved words that have predefined meanings in Python and cannot be used as identifiers. Examples include if, else, for, while, class, def, return, try, except, import, and lambda.
Interview tip: Use a short example and connect the answer to real project work.
Q8. What is the difference between interpreted and compiled languages?
Medium
Answer: Compiled languages convert the entire source code into machine code before execution. Interpreted languages execute code line by line using an interpreter. Python is primarily interpreted, although it first compiles source code into bytecode before execution by the Python Virtual Machine (PVM).
Interview tip: Use a short example and connect the answer to real project work.
Q9. What is PEP 8?
Medium
Answer: PEP 8 is the official Python style guide. It defines coding standards such as naming conventions, indentation, line length, spacing, imports, and formatting to improve code readability and maintainability.
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Q10. What is the Python Virtual Machine (PVM)?
Hard
Answer: The Python Virtual Machine (PVM) is the runtime engine that executes Python bytecode. When a Python program runs, the source code is first compiled into bytecode (.pyc files), and the PVM interprets this bytecode to execute the program. This design makes Python portable across different operating systems.
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Q11. What are the built-in data types in Python?
Easy
Answer: Python provides several built-in data types, including numeric types (int, float, complex), text (str), sequence types (list, tuple, range), mapping type (dict), set types (set, frozenset), boolean (bool), binary types (bytes, bytearray, memoryview), and NoneType.
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Q12. What is the difference between int, float, and complex data types?
Easy
Answer: The int type stores whole numbers, float stores decimal numbers, and complex stores numbers with real and imaginary parts, such as 3 + 4j.
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Q13. What is a string in Python?
Medium
Answer: A string is an immutable sequence of Unicode characters enclosed in single quotes, double quotes, or triple quotes. Strings support slicing, indexing, formatting, and numerous built-in methods for text processing.
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Q14. What is the difference between a list and a tuple?
Medium
Answer: Lists are mutable, allowing elements to be added, removed, or modified after creation. Tuples are immutable, making them faster and suitable for storing fixed collections of data that should not change.
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Q15. What is a set in Python?
Medium
Answer: A set is an unordered collection of unique elements. It automatically removes duplicate values and supports efficient operations such as union, intersection, difference, and membership testing.
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Q16. What is a dictionary in Python?
Medium
Answer: A dictionary is a mutable collection of key-value pairs. Each key must be unique, and values can be of any data type. Dictionaries provide fast lookup, insertion, and deletion operations using keys.
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Q17. What is the difference between mutable and immutable objects in Python?
Hard
Answer: Mutable objects can be modified after they are created, while immutable objects cannot. Lists, dictionaries, and sets are mutable. Strings, tuples, integers, floats, booleans, and frozensets are immutable. Understanding mutability is important for memory management and function behavior.
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Q18. What is type conversion in Python?
Medium
Answer: Type conversion is the process of converting one data type into another. Python supports implicit conversion performed automatically and explicit conversion using functions such as int(), float(), str(), list(), tuple(), set(), and dict().
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Q19. What are the different types of operators in Python?
Medium
Answer: Python supports arithmetic, comparison, assignment, logical, bitwise, identity, membership, and conditional (ternary) operators. These operators are used to perform calculations, comparisons, assignments, and logical operations.
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Q20. What is the difference between the '==' operator and the 'is' operator in Python?
Hard
Answer: The '==' operator compares whether two objects have the same value, while the 'is' operator compares whether two variables reference the exact same object in memory. Use '==' for value comparison and 'is' when checking object identity, such as comparing with None.
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Q21. What is a function in Python?
Easy
Answer: A function is a reusable block of code that performs a specific task. Functions help reduce code duplication, improve readability, and make programs easier to maintain. Functions are defined using the def keyword and can accept parameters and return values.
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Q22. What are the different types of function arguments in Python?
Medium
Answer: Python supports positional arguments, keyword arguments, default arguments, and variable-length arguments. Variable-length arguments include *args for multiple positional arguments and **kwargs for multiple keyword arguments.
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Q23. What are *args and **kwargs in Python?
Hard
Answer: *args allows a function to accept any number of positional arguments as a tuple. **kwargs allows a function to accept any number of keyword arguments as a dictionary. They make functions flexible and reusable when the number of inputs is unknown.
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Q24. What is a lambda function in Python?
Medium
Answer: A lambda function is an anonymous function defined using the lambda keyword. It is typically used for short expressions and is commonly passed to functions such as map(), filter(), sorted(), and reduce().
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Q25. What is recursion in Python?
Medium
Answer: Recursion is a programming technique where a function calls itself to solve a problem. Every recursive function must have a base case to stop further recursive calls and prevent infinite recursion.
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Q26. What are modules in Python?
Easy
Answer: A module is a Python file containing functions, classes, variables, and executable code. Modules help organize code into reusable units and can be imported into other Python programs using the import statement.
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Q27. What is the difference between a module and a package?
Medium
Answer: A module is a single Python (.py) file containing Python code. A package is a collection of related modules organized into directories. Packages help organize large applications into manageable components.
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Q28. What is Object-Oriented Programming (OOP)?
Medium
Answer: Object-Oriented Programming (OOP) is a programming paradigm that organizes code into objects containing data and methods. OOP improves code reusability, modularity, maintainability, and scalability through concepts such as inheritance, encapsulation, abstraction, and polymorphism.
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Q29. What are classes and objects in Python?
Medium
Answer: A class is a blueprint used to create objects. It defines the attributes and methods that objects will have. An object is an instance of a class that contains actual data and can invoke the methods defined in the class.
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Q30. Explain the four pillars of Object-Oriented Programming.
Hard
Answer: The four pillars of OOP are Encapsulation, which protects data by combining it with methods; Inheritance, which allows one class to acquire the properties and behavior of another; Polymorphism, which allows the same interface to have multiple implementations; and Abstraction, which hides implementation details while exposing only essential functionality.
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Q31. What is exception handling in Python?
Medium
Answer: Exception handling is the process of detecting and handling runtime errors without terminating the program. Python uses try, except, else, and finally blocks to manage exceptions and ensure the application continues to run gracefully.
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Q32. What is the purpose of try, except, else, and finally blocks?
Easy
Answer: The try block contains code that may raise an exception. The except block handles the exception. The else block executes if no exception occurs, and the finally block always executes regardless of whether an exception was raised, making it ideal for resource cleanup.
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Q33. How do you raise a custom exception in Python?
Medium
Answer: A custom exception can be raised using the raise keyword. Developers can also create custom exception classes by inheriting from the built-in Exception class to represent application-specific errors.
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Q34. What is file handling in Python?
Medium
Answer: File handling is the process of creating, opening, reading, writing, appending, and closing files. Python provides the built-in open() function and supports multiple file modes such as 'r', 'w', 'a', 'x', and 'b'.
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Q35. What are the different file modes available in Python?
Medium
Answer: Common file modes include 'r' (read), 'w' (write), 'a' (append), 'x' (create), 'rb' (read binary), 'wb' (write binary), 'r+' (read and write), and 'a+' (append and read).
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Q36. Why is the with statement used while working with files?
Medium
Answer: The with statement automatically manages resources by opening and closing files safely. It ensures that the file is properly closed even if an exception occurs, eliminating the need to explicitly call close().
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Q37. What is the difference between an iterator and an iterable?
Hard
Answer: An iterable is any object that can return an iterator using the iter() function, such as lists, tuples, and strings. An iterator is an object that implements the __iter__() and __next__() methods to return one item at a time until a StopIteration exception is raised.
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Q38. What is the purpose of the enumerate() function?
Medium
Answer: The enumerate() function returns both the index and value while iterating over a sequence. It simplifies loops by eliminating the need to manually maintain a counter.
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Q39. What is the zip() function in Python?
Medium
Answer: The zip() function combines multiple iterables into a single iterator of tuples by pairing elements with the same index. It is commonly used to iterate over multiple sequences simultaneously.
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Q40. What is the difference between shallow copy and deep copy?
Hard
Answer: A shallow copy creates a new object but shares references to nested objects with the original. A deep copy recursively copies all nested objects, creating a completely independent duplicate. Python provides the copy.copy() and copy.deepcopy() functions for these operations.
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Q41. What is a list comprehension in Python?
Medium
Answer: A list comprehension is a concise way to create lists using a single expression. It combines looping and conditional logic into one readable statement, making the code shorter and often faster than traditional loops.
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Q42. What is a dictionary comprehension?
Medium
Answer: A dictionary comprehension provides a compact way to create dictionaries using a single expression. It allows keys and values to be generated dynamically while iterating over another iterable.
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Q43. What is a generator in Python?
Hard
Answer: A generator is a special type of iterator that produces values one at a time instead of storing all values in memory. Generators are memory-efficient and are especially useful when working with large datasets or infinite sequences.
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Q44. What is the yield keyword in Python?
Hard
Answer: The yield keyword is used inside a generator function to return one value at a time while preserving the function's execution state. Unlike return, yield pauses the function and resumes execution when the next value is requested.
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Q45. What is the difference between return and yield?
Hard
Answer: The return statement immediately terminates a function and returns a value. The yield statement pauses execution, returns a value, and allows the function to resume later, making it suitable for generators and lazy evaluation.
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Q46. What is a decorator in Python?
Hard
Answer: A decorator is a function that adds or modifies the behavior of another function or method without changing its source code. Decorators are commonly used for logging, authentication, authorization, caching, validation, and performance measurement.
Interview tip: Use a short example and connect the answer to real project work.
Q47. What is a closure in Python?
Hard
Answer: A closure is a nested function that remembers and can access variables from its enclosing scope even after the outer function has finished executing. Closures are commonly used to preserve state and implement decorators.
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Q48. What is a context manager in Python?
Hard
Answer: A context manager is an object that automatically manages resources such as files, database connections, and network sockets. It is commonly used with the with statement to ensure resources are properly acquired and released, even if an exception occurs.
Interview tip: Use a short example and connect the answer to real project work.
Q49. What is the collections module in Python?
Medium
Answer: The collections module provides specialized container data types that extend Python's built-in containers. Popular classes include Counter, defaultdict, OrderedDict, deque, ChainMap, and namedtuple.
Interview tip: Use a short example and connect the answer to real project work.
Q50. What are namedtuple and defaultdict in Python?
Hard
Answer: namedtuple creates lightweight tuple subclasses with named fields, making code more readable. defaultdict is a dictionary subclass that automatically provides a default value for missing keys, eliminating the need to check whether a key exists before accessing it.
Interview tip: Use a short example and connect the answer to real project work.
Q51. What is multithreading in Python?
Hard
Answer: Multithreading is a technique that allows multiple threads to run concurrently within a single process. It is best suited for I/O-bound tasks such as file operations, network requests, and database access. Python provides the threading module to create and manage threads.
Interview tip: Use a short example and connect the answer to real project work.
Q52. What is multiprocessing in Python?
Hard
Answer: Multiprocessing allows a program to execute multiple processes simultaneously. Each process has its own memory space and Python interpreter, making it ideal for CPU-intensive tasks. The multiprocessing module enables applications to fully utilize multiple CPU cores.
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Q53. What is the Global Interpreter Lock (GIL)?
Hard
Answer: The Global Interpreter Lock (GIL) is a mechanism in CPython that allows only one thread to execute Python bytecode at a time. While it simplifies memory management, it limits true parallel execution of CPU-bound threads. It has less impact on I/O-bound applications because threads release the GIL during many blocking I/O operations.
Interview tip: Use a short example and connect the answer to real project work.
Q54. What is asyncio in Python?
Hard
Answer: asyncio is Python's built-in library for asynchronous programming. It uses an event loop along with async and await keywords to execute multiple I/O-bound operations concurrently without creating multiple threads.
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Q55. What is the difference between multithreading, multiprocessing, and asyncio?
Hard
Answer: Multithreading is best for I/O-bound tasks but is limited by the GIL for CPU-bound work. Multiprocessing creates separate processes that can run truly in parallel, making it suitable for CPU-intensive tasks. asyncio uses a single-threaded event loop to efficiently handle many asynchronous I/O operations without creating additional threads or processes.
Interview tip: Use a short example and connect the answer to real project work.
Q56. What is thread safety?
Medium
Answer: Thread safety ensures that shared data remains consistent when accessed by multiple threads simultaneously. It is achieved using synchronization mechanisms such as locks, semaphores, and thread-safe data structures.
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Q57. What are Lock, RLock, Semaphore, and Event in Python?
Hard
Answer: Lock provides mutual exclusion by allowing only one thread to access a shared resource at a time. RLock (Reentrant Lock) allows the same thread to acquire the lock multiple times. Semaphore limits the number of threads accessing a resource simultaneously. Event enables one thread to signal one or more waiting threads when a specific condition occurs.
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Q58. What is a Queue in Python?
Medium
Answer: A Queue is a thread-safe data structure used for safely exchanging data between threads or processes. The queue module provides FIFO, LIFO, and Priority Queue implementations for concurrent programming.
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Q59. How do processes communicate in Python?
Hard
Answer: Processes can communicate using multiprocessing.Queue, Pipe, shared memory, Value, Array, or synchronization primitives provided by the multiprocessing module. These mechanisms enable safe data exchange between independent processes.
Interview tip: Use a short example and connect the answer to real project work.
Q60. What are the best practices for concurrent programming in Python?
Hard
Answer: Choose multithreading for I/O-bound tasks, multiprocessing for CPU-bound tasks, and asyncio for high-concurrency asynchronous applications. Minimize shared mutable state, use synchronization primitives when needed, avoid deadlocks, use thread-safe queues for communication, handle exceptions properly, and profile your application before optimizing concurrency.
Interview tip: Use a short example and connect the answer to real project work.
Q61. What is a virtual environment in Python?
Easy
Answer: A virtual environment is an isolated Python environment that allows each project to have its own Python interpreter, packages, and dependencies. It helps avoid version conflicts between different projects and is commonly created using the built-in venv module.
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Q62. What is pip in Python?
Easy
Answer: pip is Python's default package manager. It is used to install, upgrade, remove, and manage third-party packages from the Python Package Index (PyPI) or other package repositories.
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Q63. What is SQLite and when should it be used?
Medium
Answer: SQLite is a lightweight, serverless relational database that stores the entire database in a single file. It is ideal for small applications, desktop software, mobile apps, prototypes, and local development environments.
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Q64. How do you connect Python to MySQL or PostgreSQL?
Medium
Answer: Python connects to relational databases using database drivers such as mysql-connector-python, PyMySQL, or psycopg2. Developers can also use ORMs like SQLAlchemy or Django ORM to simplify database interactions and reduce boilerplate SQL code.
Interview tip: Use a short example and connect the answer to real project work.
Q65. What is Flask?
Medium
Answer: Flask is a lightweight Python web framework used for building web applications and REST APIs. It provides routing, request handling, template rendering, and extension support while giving developers flexibility in choosing project components.
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Q66. What is Django?
Medium
Answer: Django is a high-level Python web framework that follows the Model-View-Template (MVT) architecture. It includes built-in features such as an ORM, authentication, an admin interface, form handling, security protections, and URL routing, enabling rapid web application development.
Interview tip: Use a short example and connect the answer to real project work.
Q67. What is the difference between Django and Flask?
Hard
Answer: Django is a full-featured framework with built-in authentication, ORM, admin panel, form handling, and security features, making it suitable for large applications. Flask is lightweight and minimal, allowing developers to choose only the libraries they need, making it ideal for microservices, APIs, and smaller applications.
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Q68. What is a REST API?
Medium
Answer: A REST API is a web service that follows REST architectural principles and communicates using HTTP methods such as GET, POST, PUT, PATCH, and DELETE. REST APIs commonly exchange data in JSON format and are widely used for communication between clients and servers.
Interview tip: Use a short example and connect the answer to real project work.
Q69. What is FastAPI and why is it popular?
Hard
Answer: FastAPI is a modern Python web framework designed for building high-performance APIs. It supports asynchronous programming, automatic request validation using type hints, automatic OpenAPI and Swagger documentation generation, and excellent performance comparable to Node.js and Go for many API workloads.
Interview tip: Use a short example and connect the answer to real project work.
Q70. What is SQLAlchemy?
Hard
Answer: SQLAlchemy is a powerful Python SQL toolkit and Object-Relational Mapper (ORM). It allows developers to interact with relational databases using Python objects while also supporting raw SQL queries, transactions, connection pooling, and database migrations through related tools.
Interview tip: Use a short example and connect the answer to real project work.
Q71. How is memory managed in Python?
Hard
Answer: Python automatically manages memory using private memory spaces, reference counting, and a garbage collector. Objects are created on the heap, and memory is automatically reclaimed when objects are no longer referenced, reducing the need for manual memory management.
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Q72. What is garbage collection in Python?
Hard
Answer: Garbage collection is the process of automatically identifying and removing objects that are no longer in use. Python combines reference counting with a cyclic garbage collector to detect and clean up circular references that reference counting alone cannot remove.
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Q73. What is reference counting in Python?
Hard
Answer: Reference counting is the primary memory management technique used by CPython. Every object keeps track of how many references point to it. When the reference count reaches zero, the object's memory is released automatically unless it is part of a reference cycle handled by the garbage collector.
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Q74. What is the purpose of if __name__ == "__main__"?
Medium
Answer: The special variable __name__ is set to '__main__' when a Python file is executed directly. The condition if __name__ == '__main__': ensures that specific code runs only when the file is executed as the main program and not when it is imported as a module.
Interview tip: Use a short example and connect the answer to real project work.
Q75. What is __slots__ in Python?
Hard
Answer: __slots__ is a class attribute that restricts the set of attributes instances can have. It reduces memory usage and can improve attribute access performance by preventing the creation of an instance __dict__ when dynamic attributes are not needed.
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Q76. What is the difference between __str__() and __repr__()?
Medium
Answer: __str__() returns a user-friendly string representation of an object, while __repr__() returns an unambiguous representation intended for developers and debugging. If __str__() is not implemented, Python falls back to using __repr__().
Interview tip: Use a short example and connect the answer to real project work.
Q77. How can you improve the performance of a Python application?
Hard
Answer: Performance can be improved by choosing efficient algorithms and data structures, using generators for large datasets, minimizing unnecessary object creation, leveraging built-in functions, optimizing database queries, using caching, profiling code to identify bottlenecks, and using multiprocessing or asynchronous programming when appropriate.
Interview tip: Use a short example and connect the answer to real project work.
Q78. What tools are used for profiling Python applications?
Hard
Answer: Common profiling tools include cProfile, profile, timeit, memory_profiler, tracemalloc, line_profiler, and py-spy. These tools help identify CPU, memory, and performance bottlenecks in Python applications.
Interview tip: Use a short example and connect the answer to real project work.
Q79. What are Python coding best practices?
Hard
Answer: Follow PEP 8 guidelines, write readable and modular code, use meaningful variable names, avoid global variables, handle exceptions appropriately, write unit tests, document code with docstrings, use virtual environments, manage dependencies carefully, and keep functions small and focused on a single responsibility.
Interview tip: Use a short example and connect the answer to real project work.
Q80. What are common Python interview mistakes and how can they be avoided?
Hard
Answer: Common mistakes include confusing 'is' with '==', using mutable objects as default function arguments, ignoring exception handling, writing inefficient loops instead of using built-in functions or comprehensions, misunderstanding variable scope, and neglecting time and space complexity. Understanding core Python concepts and practicing coding problems regularly helps avoid these mistakes.
Interview tip: Use a short example and connect the answer to real project work.
Quick revision checklist
- Explain the answer without reading.
- Write one small example.
- Review platform or version differences in official documentation.
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