Return Key

• The Python return keyword exits a function and instructs Python to continue executing the main program. The return keyword can send a value from a function or method, back to the main program; the returned value could be a string, a tuple, or any other object.

• Python function default return value is None, and it’s always optional to return something from a function.

• If the return keyword is placed in a loop, it will terminate the loop (迴圈會被停掉)

# return keyword

def myAddtion(a, b):
    print(a + b)

def myAddtion2(a, b):
    return a + b  # return value 方便運算

myAddtion(10, 18)
myAddtion(20, 28)
myAddtion(30, 38)

myAddtion2(10, 18) # 只有return value 要有variable 存入 --> result 1 
myAddtion2(20, 28) # 只有return value 要有variable 存入 --> result 2 
myAddtion2(30, 38) # 只有return value 要有variable 存入 --> result 3 

result1 = myAddtion2(10, 18)
result2 = myAddtion2(20, 28)
result3 = myAddtion2(30, 38)

print(myAddtion2(10, 18) + myAddtion2(20, 28) +
      myAddtion2(30, 38))  # 利用return value 可以相加
print(result1 + result2 + result3)

print(myAddtion(10, 18),  myAddtion(20, 28))  # print 出來的是none type
print(myAddtion(10, 18) + myAddtion(20, 28) + myAddtion(30, 38))  # none type

--------------------------------------------------------------------

[Running] python -u "d:\\2022_python_全攻略\\54. Parameters are local variables.py"
28
48
68
144 #print(myAddtion2(10, 18) + myAddtion2(20, 28) +  myAddtion2(30, 38))  # 利用return value 可以相加
144 #print(result1 + result2 + result3)

28  # print(myAddtion(10, 18),  myAddtion(20, 28))  # print 出來的是none type
48
None None

    print(myAddtion(10, 18) + myAddtion(20, 28) + myAddtion(30, 38))  # none type
TypeError: unsupported operand type(s) for +: 'NoneType' and 'NoneType'

#return loop stop code 

def myAddtion(a, b):
    for i in range(a):
        for j in range(b):
            if i == 2 and j == 2:
                return  # default 是none 所以不一定要寫值，loop 在 (2,2)condition會停掉
            print(i, j)

myAddtion(4,4) --> 原本預計跑到3, 3 但設定跑到 2，2 return 就stop 
-------------------------------------------------------------
[Running] python -u "d:\\2022_python_全攻略\\tempCodeRunnerFile.py"
0 0
0 1
0 2
0 3
1 0
1 1
1 2
1 3
2 0
2 1  --> 2, 2時 return