Be careful!

The list of list is modified unexpected, python

# code patch A:

list = [1,2,3,4,5,6,7]

print('list A :', list)

for i in list:

    temp = i

    if i > 5:

        temp = i + 10000

print('list A\':', list)

# code patch B:

list = [[1],[2],[3],[4],[5],[6],[7]]

new_list = []

print('\nlist B : ',list)

for i in list:

    temp = i    # will this allocate a new RAM space for var 'temp'?

    if i[0] > 5:

        temp[0] = i[0] + 1000

    new_list.append(temp)

print('list B\': ', list, end='')

print(' <-- you can see the list is changed, which is not i want.')

print('new_list:', new_list)

# code patch C:

list = [[1],[2],[3],[4],[5],[6],[7]]

new_list = []

print('\nlist C : ',list)

for i in list:

    temp = ['']    # only this line is MODIFIED than code patch B.

    temp[0] = i[0]

    if i[0] > 5:

        temp[0] = i[0] + 1000

    new_list.append(temp)

print('list C\': ', list, end='')

print(' <-- you can see the list is NOT changed.')

print('new_list:', new_list)

'''

Output:

---

list A : [1, 2, 3, 4, 5, 6, 7]

list A': [1, 2, 3, 4, 5, 6, 7]

list B :  [[1], [2], [3], [4], [5], [6], [7]]

list B':  [[1], [2], [3], [4], [5], [1006], [1007]] <-- you can see the list is changed. which is not i want.

new_list: [[1], [2], [3], [4], [5], [1006], [1007]]

list C :  [[1], [2], [3], [4], [5], [6], [7]]

list C':  [[1], [2], [3], [4], [5], [6], [7]] <-- you can see the list is NOT changed.

new_list: [[1], [2], [3], [4], [5], [1006], [1007]]

Question:

 why list B' is modified in the for loop?

'''

巴特西

The list of list is modified unexpected, python

Be careful!

The list of list is modified unexpected, python

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