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Python Interview Notes

Jul 15, 2025

Overview

This lecture covers essential Python interview questions spanning beginner to advanced levels, with explanations of key concepts, syntax, and differences between major Python features.

Python Basics & Concepts

  • Python is a popular, flexible, and widely used programming language for both beginners and experts.
  • A module is a single .py file with related functions, classes, or variables.
  • A package is a directory of modules with an __init__.py file for organization.
  • Python is primarily an interpreted language, compiling source code to bytecode before execution.
  • Benefits of Python: simplicity, versatility, rich libraries (Django, pandas, TensorFlow), community support, portability, development speed, dynamic typing, open-source.
  • Global attributes are public (global scope), protected have a single underscore (accessible, but should be avoided outside class), private have double underscores (not accessible outside the class).
  • Python is case sensitive.

Data Structures & Control Flow

  • Lists are mutable, use square brackets, allow modification; tuples are immutable, use parentheses, are more memory-efficient.
  • Slicing extracts portions of sequences using [start:stop:step] syntax.
  • For loops iterate over collections; while loops repeat until a condition is false.
  • Indentation is required in Python to define code blocks and improve readability.
  • break exits a loop; continue skips to the next iteration; pass is a placeholder.
  • Sets are unordered, mutable collections of immutable items.

Functions, Classes & OOP

  • self refers to the instance of a class, not a keyword.
  • Inheritance allows a child class to use or override parent class attributes and methods; supports single, multi-level, hierarchical, and multiple inheritance.
  • Classes are defined using the class keyword; methods and attributes are declared inside.
  • *args allows variable-length positional arguments; **kwargs for variable-length keyword arguments.***

Memory Management & Performance

  • Python manages memory via reference counting and automatic garbage collection using a private heap.
  • NumPy arrays are faster than lists for numerical operations due to C-based implementation.
  • Shallow copy shares references; deep copy duplicates objects to avoid shared references.

Built-in Tools, Libraries & Syntax

  • Common built-in modules: os, sys, math, random, datetime, json.
  • range creates lists in Python 2; xrange is a generator-like for large ranges (not in Python 3).
  • zip aggregates elements from multiple iterables.
  • Pandas: open-source library for data analysis and manipulation.
  • PEP8: style guide for writing readable Python code.

Error Handling & Documentation

  • Exception handling uses try, except, and finally blocks.
  • Runtime errors occur during program execution.
  • Docstrings (triple-quoted) document functions and classes.

Advanced Features & Libraries

  • Multi-threading uses the threading module but is limited by the Global Interpreter Lock (GIL).
  • Generators use yield to return items lazily.
  • Django and Flask are popular web frameworks; Django suits large apps, Flask for smaller, flexible projects.
  • PIP is the Python package installer.
  • Compatibility between Python 2 and 3 achieved using __future__, six/future libraries, and best practices.

Operations & Other Concepts

  • Modulus (%) returns remainder, / is floating-point division, // is floor division.
  • Type conversion functions: int(), float(), str(), list(), tuple(), set(), dict().
  • A Series (Pandas) is a 1D array; a DataFrame is a 2D table.
  • len() returns the length of objects such as strings or lists.

Key Terms & Definitions

  • Module — a single Python file containing code.
  • Package — a directory with multiple modules and an __init__.py.
  • Bytecode — intermediate, low-level code executed by the Python interpreter.
  • Inheritance — mechanism for a class to inherit attributes/methods from another class.
  • GIL (Global Interpreter Lock) — mutex limiting thread execution to one at a time in CPython.
  • PEP8 — Python style guide for readable and consistent code.
  • Docstring — triple-quoted string documenting code.
  • Generator — function yielding values with yield, creating iterators.

Action Items / Next Steps

  • Review Python syntax, key data structures, and OOP concepts.
  • Practice writing basic and advanced Python programs.
  • Explore built-in modules and popular libraries like pandas, NumPy, Django, Flask.
  • Follow PEP8 for code style in practice problems.
  • Prepare for common interview coding exercises (e.g., Fibonacci series, list/tuple operations).

Full transcript