No, input is definitely a reserved keyword. It's just that python does not raise any error if you want to override the value, but that's still a very bad habit.

$ python 
Python 2.7.13 (default, Jan 12 2017, 17:59:37) 
[GCC 6.3.1 20161221 (Red Hat 6.3.1-1)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> input
<built-in function input>
>>> input = 10
>>> input
10