Lecture Notes: Advanced Python Features

Introduction

• Topic: Hidden and powerful features in Python
• Objective: Understand five key Python features to appear more professional

1. Anonymous Variable

• Underscore (_): Used as a placeholder for variables whose values are not needed.
• Use Cases:
  • For Loop: Replace unused loop variable.

    for _ in range(10):
        print("Do this")
    

  • Unpacking Coordinates: Avoid declaring unused variables.

    x, _ = coordinate
    x, _, z = larger_coordinate
    

  • List Comprehension: Avoid declaring unused variables.

    second_elements = [b for _, b in list_of_pairs]
    

• Benefits: Prevents linting errors and improves code clarity.

2. Else Statement in Loops

• While/For Loops with Else: The else block executes only if the loop is not terminated by a break statement.
• Example:

  for item in items:
      if item == 'B':
          break
  else:
      print("Do something here")
  

  • Output: else block runs if 'B' is not found and loop completes.
• Use Case: Useful for determining loop exit status without using additional flags.

3. Walrus Operator

• Operator: := (introduced in Python 3.8).
• Function: Assigns a value while using it in an expression.
• Examples:
  • While Loop:

    while (data := next(generator)) != -1:
        process(data)
    

  • List Comprehension:

    results = [result for x in range(10) if (result := f(x)) > 3]
    

• Benefits: More readable and efficient code.

4. Argument and Parameter Unpacking

• Single Asterisk (*): Unpacks iterable objects (e.g., lists, tuples).

  def func(a, b, c, d):
      pass
  values = [1, 2, 3, 4]
  func(*values)
  

• Double Asterisk (**): Unpacks dictionaries for keyword arguments.

  def func(key, target):
      pass
  kwargs = {'key': 5, 'target': 10}
  func(**kwargs)
  

• Benefits: Clean and flexible code for handling multiple arguments.

5. Default Dictionary

• Library: collections module.
• Class: defaultdict
• Function: Automatically assigns a default value to non-existing keys.
• Example:

  from collections import defaultdict
  
  def default():
      return 0
  
  char_count = defaultdict(default)
  for char in string:
      char_count[char] += 1
  

• Benefits: Simplifies code by removing the need for manual checks for key existence.

Conclusion

• Summary: Discussed five advanced Python features for professional coding.
• Additional Resources: Mentioned a software development program for further learning.