有人可以幫助我了解此Python代碼如何工作

Question

這是我在學校上課時的一堂課的代碼，我對列表的打印方式感到困惑，因為它一直以“ None”結尾。

def printlist(myList, pointer):
    print("The List is: ", myList)
    print("Pointer length: ", pointer)
    print("The List length is: ", len(myList))
    print("The List printed properly:")
    print(printlistproperly(myList))

def printlistproperly(myList):
    thelength = len(myList)
    for i in range(thelength):
        print(i, " ", myList[i])

def popin(myList,pointer):
    myList.append(input("Enter a value: "))
    pointer = len(myList)-1
    return myList, pointer

def main():
    myList = ["Ford","Toyota","Mustang"]
    pointer = len(myList)-1
    myList,pointer = popin(myList,pointer)
    printlist(myList, pointer)

結果是：

>>> main()
Enter a value: Dodge
The List is:  ['Ford', 'Toyota', 'Mustang', 'Dodge']
Pointer length:  3
The List length is:  4
The List printed properly:
0   Ford
1   Toyota
2   Mustang
3   Dodge
None

我的真正問題是...末尾沒有什么？ 它從何而來？ 我該如何解決？

Answer 1

在功能printlist打印功能的結果printlistproperly ，它沒有返回。 因此，您得到None 。 解決方案：只需調用printlistproperly(myList) （不使用print ）。

def printlist(myList, pointer):
    print("The List is: ", myList)
    print("Pointer length: ", pointer)
    print("The List length is: ", len(myList))
    print("The List printed properly:")
    printlistproperly(myList)