Phthon Decorator

I just start to learn the Python, I don't know how those example below work. Can anyone tell me what each example output and meaning , help me to better understand the decorator?Thank you very much. Execute all the decorator/package examples accompanied. Make useful notes for yourself including what you learned in each example. Thank you very much.

import unittest

# 1. Decorator1 # idea 1 # python can return a method # idea 2 # python can nest methods

def parent(num): def first_child(): return "Printing from the first_child() function."

def second_child(): return "Printing from the second_child() function."

# Python Style: Don't afraid of using exceptions if num == 10: return first_child else: return second_child # 2. Decorator 2 # decorator is a pattern to # 1. get a function # 2. returns wrapper (inner function) that wraps the inner function. def my_decorator2(some_function): def wrapper(): result = some_function() return result return wrapper def just_some_function2(): print("Wheee!") # 3. Decorator 3 # syntactic sugar def my_decorator3(some_function): def wrapper(num): if num == 10: value = "Yes!" else: value = "No!" result = some_function() return value + ":" + result return wrapper

@my_decorator3 def just_some_function3(): return "Wheee!" just_some_function3(10)

# 4. Decorator 4 # syntactic sugar def outside_decorator(expr): def my_decorator4(some_function): def wrapper(num): if num == 10: value = "Yes!" else: value = "No!" result = some_function() return expr + ":" + value + ":" + result return wrapper return my_decorator4

@outside_decorator("Python decorators") def just_some_function4(): return "Wheee!"

class DecoratorTests(unittest.TestCase):

def test_decorator1(self): foo = parent(10) bar = parent(11) self.assertEqual(foo(), "Printing from the first_child() function.") self.assertEqual(bar(), "Printing from the second_child() function.")

def test_decorator2(self): def just_some_function(): return "Wheee!" expected_string = "Wheee!" just_some_function = my_decorator2(just_some_function) self.assertEqual(just_some_function(), expected_string) def test_decorator3(self): def just_some_function(): return "Wheee!" expected_string = "Yes!:" + "Wheee!" self.assertEqual(just_some_function3(10), expected_string) def test_decorator4(self): @outside_decorator("Python decorators") def just_some_function4(): return "Wheee!" expected_string = "Python decorators:" \ "Yes!:" + "Wheee!" self.assertEqual(just_some_function4(10), expected_string) if __name__ == '__main__': unittest.main()