Python函数调用后主函数列表变量a异常改变问题求助

Hey there! Let's break down why your original list a is changing even though you didn't intend to modify it in the mhmArgSort function.

The Core Issue: Mutable Object References in Python #

In Python, lists are mutable objects. When you write myNumList = myNumListInput inside your function, you're not creating a brand new copy of the input list—you're just making myNumList point to the exact same list as myNumListInput (they share the same memory address).

So when you execute myNumList[smallestNumIndex] = 100000000000, you're directly altering the original list a from your main scope, because they're the same underlying object.

The Fix: Work With a Copy of the List #

To avoid modifying the original list, you need to create a shallow copy of the input list before performing any operations on it. Here are three simple ways to do this:

• Use the built-in copy() method: myNumList = myNumListInput.copy()
• Use the list() constructor: myNumList = list(myNumListInput)
• Use slicing syntax: myNumList = myNumListInput[:]

Modified Working Code #

Here's your updated function with the copy fix applied:

def mhmArgSort(myNumListInput):
    # Create a copy of the input list to avoid altering the original
    myNumList = myNumListInput.copy()
    cnt=0
    endCnt=len(myNumList)
    NumListSortedIndices=[]
    for cnt1 in range(len(myNumList)):
        smallestNum=100000000000
        smallestNumIndex=0
        for cnt in range(len(myNumList)):
            if myNumList[cnt]<smallestNum:
                smallestNum=myNumList[cnt]
                smallestNumIndex=cnt
        NumListSortedIndices.append(smallestNumIndex)
        myNumList[smallestNumIndex]=100000000000
    return NumListSortedIndices

a=[1,2,3,4,-1,0,3]
print(a)
b=mhmArgSort(a)
print(a)
print(b)

Updated Output #

[1, 2, 3, 4, -1, 0, 3]
[1, 2, 3, 4, -1, 0, 3]
[4, 5, 0, 1, 2, 6, 3]

Now your original list a remains unchanged, and you get the correct sorted indices in b as expected.

内容的提问来源于stack exchange，提问作者Moe