• Python allows function arguments to have default values. If the function is called without the argument, the argument gets its default value.

  • default argument = 預設argument, 一般是none, 如果有給定值會抓給定argument , 不然會抓default argument

• When we define default arguments, we have to put all of them at the end; otherwise, we will see:

  • SyntaxError: non-default argument follows default argument

    • default arugment 要放在最後面，不然會show 出 syntax Error
    • def sum(n1=2, n2=3)
    • def sum(n2=3, n1)

    

• When we define functions, we can give default arguments; when we invoke functions, we can give keyword arguments. (They both look alike, but they are different !!)

  • default argument 是我們在寫function 中 定義好先預設的argument

  • keyword argument 是要跑function 時，給定要代入 argument 優先性會先吃 keyword arguement input

    • def sum(n1=0, n2=0): # default argument return n1 + n2

    print(sum(n1=200)) #keyword argument

# default argument

def sum(n1, n2):
    return n1 + n2

print(sum(2, 3))
# print(sum(2, ))  # show missing 1 required positional argument

 def sum(n3=5, n4): #non-default argument follows default argument
 return n3 * n4

 print(sum(2, )) #它會不知道你是要用 argument 代入還是default arguemnt 代入

def sum(n3, n4=5):  # default arguemnt 放在最後 OK 
    return n3 * n4

print(sum(2, ))  # 抓 n3 = 2, n4 原本argument 沒寫, 用default n=5 代入

----------------------------------------
10

# default and keyword argument comparison

def sum(n1=0, n2=0): # default argument
    return n1 + n2 

#keyword argument
print(sum(n1=200))

---------------------------------
200