15-Decorators

Higher Order Functions

• We can pass functions as arguments inside other functions
• We can also nest functions inside other functions
• We can also return functions from other functions
• Inner functions can access outer functions scope (variables) aka closure

Colt Steele's "Python Course - Higher Order Functions" video has a great example of closure

Decorators

• Decorators are functions that wrap other functions enhancing their behaviors
• They then return the wrapper function, not the func that has been wrapped
• They are examples of Higher Order Functions
• They have their own special syntax using @ (syntactic sugar), though it's not mandatory to use them

Decorators with Different Signatures

What to do if the wrapped functions take different number of arguments?

In such cases we pass args and kwargs as the function parameters for the wrapper function so it can take none to any number of arguments.

# BOILER PLATE FOR A DECORATOR FUNCTION

from functools import wraps

def main(fn):
  @wraps(fn)
  def wrapper(*args, **kwargs):
    # some tasks
    result = fn(*args, **kwargs)
    # some tasks
    return result
  return wrapper

@main
def function_name():
  return 'something'

function_name()

Decorators Functions Taking Arguments

• We can also create decorator functions that take arguments
• We have to add an extra layer of function which will take the argument passed and return a new wrapper function to wrap our fn to be wrapped

from functools import wraps

def main(val):

  def inner(fn):
    @wraps(fn)
    def wrapper(*args, **kwargs):
      # do something with `val` maybe
      result = fn(*args, **kwargs)
      # some tasks
      return result
    return wrapper
  return inner

@main(some_val)
def function_name():
  return 'something'

function_name()