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#!/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?
662
Return Value of insert() function in Python insert() method just inserts the element in the list and updates the list and so does not return any value or we can say that insert() method returns None.
append() is an in-place operation, meaning that it modifies the state of the list , instead of returning a new list object. All functions in Python return None unless they explicitly return something else.
insert always has O(n) (linear) complexity. Also, a Python list is not exactly the same as a C++ list. In fact, a Python list is more comparable to a C++ std::vector if anything.
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.
67
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]
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