Python’s insert returning None?

#!/usr/bin/python

numbers = [1, 2, 3, 5, 6, 7]

clean = numbers.insert(3, 'four')

print clean
# desire results [1, 2, 3, 'four', 5, 6, 7]

I am getting “None”. What am I doing wrong?

Answers:

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Method 1

Mutating-methods on lists tend to return None, not the modified list as you expect — such metods perform their effect by altering the list in-place, not by building and returning a new one. So, print numbers instead of print clean will show you the altered list.

If you need to keep numbers intact, first you make a copy, then you alter the copy:

clean = list(numbers)
clean.insert(3, 'four')

this has the overall effect you appear to desire: numbers is unchanged, clean is the changed list.

Method 2

The insert method modifies the list in place and does not return a new reference. Try:

>>> numbers = [1, 2, 3, 5, 6, 7]
>>> numbers.insert(3, 'four')
>>> print numbers
[1, 2, 3, 'four', 5, 6, 7]

Method 3

The list.insert() operator doesn’t return anything, what you probably want is:

print numbers

Method 4

insert will insert the item into the given list. Print numbers instead and you’ll see your results. insert does not return the new list.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0