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below is a small part of a larger program. I wonder why "word_list" changes from [['dog', 'cat'], ['fish', 'lion']] to [[1, 'dog', 'cat'], [2, 'fish', 'lion']]? The whole purpose of the function "add_values_to_nested_list" is to add the values one and two to the "word_list" and then create the "new_list". But I do not want the "word_list" to change and I do not get why it does so?. I am calling another function further down in the program with the argument "word_list" so I want the "word_list" to be intact but also create the "new_list". I have used print() just to show how the word_list changes.

def add_values_to_nested_list(list):
    lenght_list = len(list)
    a = 0
    while a<lenght_list:
        list[0+a].insert(0, 1+a)
        a +=1
    return list

word_list = [['dog', 'cat'], ['fish', 'lion']]
print(word_list) 

new_list = add_values_to_nested_list(word_list)
print(new_list)

print(word_list) #Why does the "word_list" change to [[1, 'dog', 'cat'], [2, 'fish', 'lion']], I want it be intact.

Here is the same type of problem but simplified. How do I create the "new_list" but still keep the "original_list" intact to use later on in the program. The print() on lines 8,10,13 are just to show what I mean.

def add_value_to_list(original_list):
    new_list = original_list
    new_list.append(2)
    return new_list


original_list = [1]
print(original_list)

new_list = add_value_to_list(original_list)
print(new_list)

print(original_list)
Hellstrom
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  • Your code does not create a new list. Your snippets have exactly one list in it, which gets modified several times. Your `new_list` name just makes another reference to that same list. If you want to make a copy of a list, use `list[:]`. – Tim Roberts Nov 30 '21 at 23:57

0 Answers0