@alexandrpi,

is tests for identity, not equality.

>>> t = 0.0
>>> t is 0.0
False
>>> 0 is 0.0
False
>>> id(0)
140060787693792  # not the same id as 0.0
>>> id(0.0)
140060789559680  # not the same id as 0
>>> 0 == 0.0
True

• https://stackoverflow.com/questions/22885931/when-if-ever-to-use-the-is-keyword-in-python

Thanks for letting me know.. I have not looked at the PEP8 documentation.