Error numbers in tools such as pep8 and pyflakes (although flake8 adds
them to pyflakes) are usually not made to be entirely successive. For
the most part, there are groupings of errors. The best explanation of
this is pep8's documentation:
http://pep8.readthedocs.org/en/latest/intro.html#error-codes
Anything starting with E1 is related to indentation, anything starting
with E2 is related to whitespace. These are conceptually classes of
errors. PyLint also follows this convention if I remember correctly
and you would do well to do the same. The error codes that Flake8 adds
to PyFlakes follow that convention as well.