removed a singleton-comparison pitfall

[NaelsonDouglas]

Problem:
The code had a pitfall known as singleton-comparison.
In Python, when comparing singletons, like None, True or False, it's safer to use the 'is' operator instead of '=='.
Constructions like:

foo == True
bar == False
foobar == None

Are preferred to be written as:

foo is True
bar is False
foobar is None

These discussions give some highlight into this topic
https://stackoverflow.com/questions/1011431/common-pitfalls-in-python
https://stackoverflow.com/questions/2209755/python-operation-vs-is-not

Solution:
This pull request simply removes this pitfall from the code.