Pass a list to a function __ function

When a list is passed to a function, because the list is a Mutable object, the contents of the list are returned to change after the function call.

def main ():
    x =1
    y = [1,2,4]
    m (x, y)
    print ("x is", x)
    print ("Y[0", Y[0])
def m (number, number s): Number
    = 1001
    numbers[0] = 5555

main ()
#运行结果
x is  1  
y[0] is 5555 #

When M is called, X remains 1, but y[0] is changed to 5555 because Y and numbers all point to the same list object. When M (X,y) is invoked, the reference values of x and Y are passed to number and numbers. Because y contains a reference value that points to a list, numbers now contains the same reference value that points to the same list. English number is immutable, so in a function that bain it creates an instance, and the original instance outside the function is not changed. Therefore, outside of the function x is still 1.

#以上照抄了书本原文, the truth understand, but not very thorough understanding, for the record.

To use a list as a default function

def add (x, LST = []):
    if x to LST:
        lst.append (x) return
    LST
def main ():
    List1 = Add (1) #lst default value [] is created, add (1) is added to LST
    print (list1)

    List2 = Add (2) #lst是 [1] instead of [],add (2) LST becomes [1,2]
    print (list2)

    List3 = Add (3, [One, one,]) #给出列表参数 [11,12,13,14] and pass this list to the LST
    print (list3)

    list4 =add (4) #默认列表参数被使用, because the default list is [ 1,2], so after calling Add (4), the default list becomes [1,2,4]
    print (LIST4)

main ()
#运行结果
[1]
[1, 2] 
[11, 12, 13, 14, 3]
[1, 2, 4]

If you want the default list to be [] each time the function is called, you can modify it to the following code

def add (x, LST = none): 
    if LST = = None:
        LST = []
    if x in LST:
        lst.append (x) return
    lst
D EF Main ():
    List1 = Add (1)
    print (list1)

    List2 = Add (2)
    print (list2)

    list3 = Add (3, [11, 12, 13, 1 4]
    print (LIST3)

    list4 =add (4)
    print (LIST4)

main ()
#运行结果
[1]
[2]
[11, 12 , 3]
[4]