Python Language Tutorial => Functions

Functions in Python provide organized, reusable and modular code to perform a set of specific actions. Functions simplify the coding process, prevent redundant logic, and make the code easier to follow. This topic describes the declaration and utilization of functions in Python.

Python has many built-in functions like print(), input(), len(). Besides built-ins you can also create your own functions to do more specific jobs—these are called user-defined functions.

5 basic things you can do with functions:

• Assign functions to variables

  def f():
    print(20)
  y = f
  y()
  # Output: 20
  

• Define functions within other functions (Nested functions )

  def f(a, b, y):
      def inner_add(a, b):      # inner_add is hidden from outer code
          return a + b
      return inner_add(a, b)**y
  

• Functions can return other functions

  def f(y):
      def nth_power(x):
          return x ** y
      return nth_power    # returns a function
  
  squareOf = f(2)         # function that returns the square of a number           
  cubeOf = f(3)           # function that returns the cube of a number
  squareOf(3)             # Output: 9
  cubeOf(2)               # Output: 8
  

• Functions can be passed as parameters to other functions

  def a(x, y):
      print(x, y)
  def b(fun, str):        # b has two arguments: a function and a string 
      fun('Hello', str)
  b(a, 'Sophia')           # Output: Hello Sophia
  

• Inner functions have access to the enclosing scope (Closure )

  def outer_fun(name):
      def inner_fun():     # the variable name is available to the inner function
          return "Hello "+ name + "!"
      return inner_fun
  greet = outer_fun("Sophia")
  print(greet())            # Output: Hello Sophia!
  

Additional resources

• More on functions and decorators: https://www.thecodeship.com/patterns/guide-to-python-function-decorators/