[FIXED] Type error when trying to extend a list in Python

Issue

I need to understand why :

years = range(2010,2016)
years.append(0)

is possible, returning :

[2010,2011,2012,2013,2014,2015,0]

and

years = range(2010,2016).append(0)

or

years = [0].extend(range(2010,2016))

doesn't work ?

I understand that it is a type error from the message I got. But I'd like to have a bit more explanations behind that.

Solution

You are storing the result of the list.append() or list.extend() method; both alter the list in place and return None. They do not return the list object again.

Do not store the None result; store the range() result, then extend or append. Alternatively, use concatenation:

years = range(2010, 2016) + [0]
years = [0] + range(2010, 2016)

Note that I'm assuming you are using Python 2 (your first example would not work otherwise). In Python 3 range() doesn't produce a list; you'd have to use the list() function to convert it to one:

years = list(range(2010, 2016)) + [0]
years = [0] + list(range(2010, 2016))

Answered By - Martijn Pieters