rahul24tech/python-interview-prep

Python Concepts and Examples

This README file provides an overview of various Python concepts and examples to help you prepare for your day 2 prep and beyond.

String Manipulation

• Reverse a String: Reverse a string without using any built-in method.

  str1 = 'Rahul'
  str2 = ''
  for i in str1:
      str2 = i + str2
  
  print('str1 is', str1)
  print('str2 is', str2)

• Split and Join a String: Split a string by spaces and join it back.

  str1 = 'Rahul'
  result = str1.split(' ')
  res = ''.join(result)
  print(res)
  print(result)

List Operations

• Sort a List: Sort a list of numbers.

  lst = [1, 5, 0, 7, 6, 3, 2]
  lst.sort()
  print(lst)

• Clear a List: Clear all elements from a list.

  lst = [1, 5, 0, 7, 6, 3, 2]
  lst.clear()
  print(lst)

• Reverse a List: Reverse a list using slicing.

  lst = [1, 5, 0, 7, 6, 3, 2]
  rev = lst[::-1]
  print(rev)

• Concatenate Two Lists: Combine two lists element-wise.

  lst1 = ['W', 'a', 'w', 'b']
  lst2 = ['e', ' ', 'riting', 'log']
  result = [x + y for x, y in zip(lst1, lst2)]
  print(result)

• Square Each Element in a List: Square each element in a list using different methods.

  • Method 1:

    lst = [1, 5, 0, 7, 6, 3, 2]
    result = map(lambda x: x * x, lst)
    print(list(result))

  • Method 2:

    lst = [1, 5, 0, 7, 6, 3, 2]
    print([i * i for i in lst])

• Find Odd Numbers Using List Comprehension: Identify odd numbers in a list using list comprehension.

  x = [1, 5, 4, 3, 2]
  print([i for i in x if i % 2 != 0])

• Minimum Value in a List Using Lambda Function: Find the minimum value in a list using a lambda function.

  x = [1, 5, 4, 3, 2]
  print(min(x, key=lambda x: x))

• Convert List of Characters to a String of Characters: Convert a list of characters into a single string.

  lst = ['My', 'name', 'is', 'Rahul', 'Kumar']
  print(','.join(lst))

Dictionary and Data Types

• Dictionary vs. Ordered Dictionary:

  • Regular dictionary: Order of elements is maintained by the hash value of keys.
  • OrderedDict: Uses a doubly linked list to maintain the order of elements.

• Set vs. Frozenset:

  • Set is a mutable object.
  • Frozenset is an immutable object.

• Tuple Type Checker:

  i = 1, 2, 4, 5, 8
  k = (1, 2, 4, 5, 8)
  print(type(k))

Functions and Keywords

• Factorial Using Recursion:

  def fact(n):
      if n == 1:
          return n
      else:
          return n * fact(n - 1)
  
  print(fact(6))

• Use of Continue Keyword: Skip even numbers and print odd numbers.

  lst = [1, 5, 0, 7, 6, 3, 2]
  for i in lst:
      if i % 2 == 0:
          continue
      print(f'odd number {i}')

• Use of Assignment Expressions (:=) in Python: Example of using the "walrus operator".

  names = ["Jacob", "Joe", "Jim"]
  
  if (name := input("Enter a name: ")) in names:
      print(f"Hello, {name}!")
  else:
      print("Name not found.")

Python File Types

• .py vs. .pyc:
  • .py: Contains source code.
  • .pyc: Contains bytecode.
  • Process:
    • Python program is executed.
    • Python interpreter checks for compiled files.
    • If .pyc file is found, Python virtual machine executes it.
    • If not found, checks for .py file, compiles it into .pyc, and then executes it.

Stateful vs. Stateless

• Stateful:

  • Stores authorization information on the server side.

• Stateless:

  • Stores authorization information on the client side along with a signature in the form of a token.

Day 2 Prep

Compiler vs. Interpreter

• Compiler:

  • Translates source code into machine code.

• Interpreter:

  • In Python, source code (.py) is compiled into bytecode (.pyc), stored in the directory named __pycache__.
  • Python interpreter (also known as Python virtual machine) reads bytecode and translates it into machine code.
  • Python is an interpreted language.

What is Garbage Collector in Python?

• Garbage Collector:
  • Removes unused memory from Python's private heap space, freeing up memory for heap space.
  • Has two components:
    • Reference Count:
      • When objects are assigned to a variable, the reference count increases.
      • When references or objects are deleted, the reference count decreases.
      • When the reference count equals zero, the memory is released immediately.
    • Cyclic Garbage Collection:
      • Handles memory cleanup for circular references.

Module vs. Package

• Module:

  • A file containing Python code and executable code (.py).
  • Modules can be imported using import.

• Package:

  • A collection of modules.
  • If a directory contains an __init__.py file, it is considered a Python package.

Built-In Data Types in Python

• Numeric Types:

  • int: Integer values (both positive and negative).
  • float: Floating-point numbers (decimal numbers).
  • complex: Complex numbers (real and imaginary parts).

• Sequence Types:

  • str: Strings (sequences of characters).
  • list: Lists (ordered sequences of elements).
  • tuple: Tuples (ordered, immutable sequences of elements).

• Mapping Type:

  • dict: Dictionaries (collections of key-value pairs).

• Set Types:

  • set: Sets (unordered collections of unique elements).
  • frozenset: Immutable sets (unordered collections of unique elements).

• Boolean Type:

  • bool: Boolean values (True or False).

• Binary Types:

  • bytes: Sequences of bytes (immutable).
  • bytearray: Sequences of bytes (mutable).
  • memoryview: Views of an array's data in memory.

• None Type:

  • None: Represents a null or absent value.

Sort List Without Using Built-In Method

• Bubble Sort:

  def bubble_sort(arr):
      n = len(arr)
      for i in range(n):
          swapped = False
          for j in range(0, n - i - 1):
              if arr[j] > arr[j + 1]:
                  # Swap the elements if they are in the wrong order
                  arr[j], arr[j + 1] = arr[j + 1], arr[j]
                  swapped = True
          # If no elements were swapped, the list is already sorted
          if not swapped:
              break
      return arr
  
  my_list = [5, 2, 9, 1, 7]
  bubble_sort(my_list)
  print(my_list)  # Output: [1, 2, 5, 7, 9]

Join Method in Python

• Join Method:
  • Converts a list or tuple into a string.

  elements = ['Hello', 'World']
  result = ' '.join(elements)
  print(result)  # Output: "Hello World"

Lambda Function That Takes Any Number of Arguments

• Example:

  lam = lambda *args: ''.join(args)
  print(lam("Hello", " ", "World"))  # Output: "Hello World!"