Python Interview Questions and Answers

Python Interview Questions & Answers

Preparing for Python interviews? This comprehensive guide features frequently asked questions, in-depth explanations, and practical code examples to help you build confidence and clarity. All code text is explicitly styled in black for readability.

Core Python Fundamentals

• What are Python's core data types?
  Examples include int, float, str, list, tuple, dict, set, and bool.
• What is list slicing?
  You can slice sequences: s[1:5:2] picks elements from index 1 to 4 in steps of 2.
• Explain mutability vs immutability.
  Mutable types (like lists, dicts) can change; immutable types (like strings, tuples) cannot.

Control Flow & Functions

• Explain *args and **kwargs.
  Use them for variable numbers of positional or keyword arguments.
• What are lambda functions?
  Anonymous single-expression functions defined with lambda.
• Generators vs list comprehensions?
  Generators use yield, produce lazy sequences, and save memory.

Object-Oriented Programming

• What is method overloading and overriding in Python?
  Python doesn’t natively support overloading; last definition wins. Overriding occurs when a subclass defines a method with the same name.
• Describe @classmethod vs @staticmethod.
  @classmethod takes the class as its first argument; @staticmethod takes none.
• Explain __str__ and __repr__.
  __str__ provides readable output; __repr__ gives an unambiguous representation for debugging.

Modules & Libraries

• How to manage dependencies in Python?
  Use pip and requirements.txt or tools like poetry/pipenv.
• Explain __init__.py in packages.
  It marks a directory as a Python package and can run initialization code.
• Popular built-in modules to know?
  Modules like itertools, collections, functools, os, and sys.

Concurrency & Performance

• What is the GIL?
  The Global Interpreter Lock ensures only one thread executes Python bytecode at a time.
• Multithreading vs multiprocessing?
  Threads share memory; processes don’t. Use threads for I/O-bound tasks and processes for CPU-bound tasks.

Code-Based Interview Questions

1. Reverse a string without slicing.
   

   def reverse_str(s):
       res = ''
       for ch in s:
           res = ch + res
       return res
   
   print(reverse_str("coding"))  # Output: gnicod
   

2. Merge two sorted lists.
   

   def merge_sorted(a, b):
       i = j = 0
       res = []
       while i < len(a) and j < len(b):
           if a[i] < b[j]:
               res.append(a[i]); i += 1
           else:
               res.append(b[j]); j += 1
       res.extend(a[i:]); res.extend(b[j:])
       return res
   
   print(merge_sorted([1,3,5], [2,4,6]))  # Output: [1, 2, 3, 4, 5, 6]
   

3. Check balanced parentheses.
   

   def is_balanced(expr):
       stack = []
       pairs = {'(': ')', '[': ']', '{': '}'}
       for ch in expr:
           if ch in pairs:
               stack.append(ch)
           elif ch in pairs.values():
               if not stack or pairs[stack.pop()] != ch:
                   return False
       return not stack
   
   print(is_balanced("({[]})"))  # Output: True
   print(is_balanced("([)]"))    # Output: False
   

4. Find the most frequent element.
   

   from collections import Counter
   
   def most_freq(lst):
       cnt = Counter(lst)
       return cnt.most_common(1)[0][0]
   
   print(most_freq([1,2,2,3,3,3,2]))  # Output: 3
   

5. Flatten a nested list.
   

   def flatten(lst):
       flat = []
       for el in lst:
           if isinstance(el, list):
               flat.extend(flatten(el))
           else:
               flat.append(el)
       return flat
   
   print(flatten([1, [2, [3, 4]], 5]))  # Output: [1, 2, 3, 4, 5]
   

Conclusion

This guide provides in-depth coverage of Python interview topics—core language features, OOP, modules, concurrency, and critical coding challenges. Practicing these examples with black-styled code will ensure clarity and focus while preparing you thoroughly for your next technical interview. Good luck!