Functions

def <function_name>(<function_name_without_parantheses>):

• Functions are first-class objects, which means that
  • functions are objects - they can be referenced to, passed to a variable, and returned from other functions as well.
  • functions can be defined inside another function - an inner function - and can also be passed as an argument to another function.
    • Inner functions only exist inside the parent() function as local variables.

"""<another_function_name> = <function_name>()
function() := function
function := object
"""
def inc(x):
  return x + 1

def dec(x):
  return x - 1

def operate(func, x):
  result = func(x)
  return result

"""Inner function
"""

def parent():
  print("Printing from the parent() function")
  
  def first_child():
    print("Printing from the first_child() function")

  def second_child():
    print("Printing from the second_child() function")

  second_child()
  first_child()

parent()

• When you call a regular function, it gets a private namespace where its local variables are created. When the function reaches a return statement, the local variables are destroyed and the value is returned to the caller. A later call to the same function creates a new private namespace and a fresh set of local variables.

First-class object

• It is a program entity that can be
  • created at runtime
  • assigned to a variable or element in a data structure
  • passed as an argument to a function
  • returned as the result of a function.