區域函數

可以再函數內再定義函數，將演算組成更小的組織重複利用

def function1():
    # outer function     
    print ("Hello from outer function")
    def function2():
        # inner function
        print ("Hello from inner function")
    function2()

function1()

為何要用區域函數：
封裝
closure

Lambda 函數

可創建一個短小的匿名函數，出於語法限制，只能有一個單獨表達式

#%% Lambda Expressions
def make_incrementor(n):
return lambda x: x + n

f = make_incrementor(42)
f(0)
f(1)

Lambda 函數的另一個功能，可以當作一個小函數物件 (function object) 傳入其他函數引數built-in function 很常使用 lambda 來當作運算條件，填入key 中

pairs = [(1, 'one'), (2, 'two'), (3, 'three'), (4, 'four')]
pairs.sort(key=lambda pair:pair[1])
pairs

students = [ ('Che', 10), ('Yo', 20), ('HowHow', 30)]
max(students,key=lambda i: i[1])

函數註解

• Documentation strings
• 型別提示

Documentation strings

def my_function():
    """Do nothing, but document it.    
    
    No, really, it doesn't do anything.    
    """    
    pass
    
print(my_function.__doc__)

型別提示

• : argument type
• -> return type

def f(ham: str, eggs: str = 'eggs') -> str:
    print("Annotations:", f.__annotations__)
    print("Arguments:", ham, eggs)
    return ham + ' and ' + eggs
    
f('spam')
f.__annotations__

& https://docs.python.org/3.7/tutorial/controlflow.html#defining-functions