reading-notes

List Comprehension

Reading

• List Comprehensions
• AUDIO: Debugging with PySnooper

Reference

• Primer on Decorators

Notes

List Comprehensions

• Can be used to replace loops when needing to create new lists
• Syntax

my_new_list = [ expression for item in list ]

• First is the expression we’d like to carry out
  • expression inside the square brackets
    • Expression just means do something to the item in the list
      • EX: multiples_of_three = [x*3 for x in range(10)]
      • You can even call functions within the list comprehension to act as your expression
• Second is the object that the expression will work on
  • item inside the square brackets
• Finally, we need an iterable list of objects to build our new list from
  • list inside the square brackets.

Python Decorators

• A decorator is a function that takes another function and extends the behavior of the latter function without explicitly modifying it
  • A decorator wraps a function, modifying its behavior
• Functions are first-class objects in Python
  • This means that functions can be passed around and used as arguments

• Uses @ symbol as syntactic sugar, referred to a pie syntax to show the decorator function and pass it to the function below

  def my_decorator(func):
      def wrapper():
          print("Something is happening before the function is called.")
          func()
          print("Something is happening after the function is called.")
      return wrapper
  
  @my_decorator
  def say_whee():
      print("Whee!")
  

  • @my_decorator is the same as setting say_whee = my_decorator(say_whee)
• If you want to pass a function that takes arguments into a decorator function, you will need to use *args and **kwargs
  • These will accept an arbitrary number of positional and keyword arguments
  • Make sure that the wrapper function returns the return value of the decorated function

  def do_twice(func):
    def wrapper_do_twice(*args, **kwargs):
        func(*args, **kwargs)
        return func(*args, **kwargs) # wrapper function needs to return the return value of the decorated function
    return wrapper_do_twice
  
  @do_twice
  def return_greeting(name):
      print("Creating greeting")
      return f"Hi {name}"
  
  return_greeting("Adam")
  # Creating greeting
  # Creating greeting
  # 'Hi Adam'