Fix use of mutable values as default function parameter value

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
Whitespace cleanup according to PEP 8

Signed-off-by: Esben Haabendal <esben@haabendal.dk>
Merge pull request #14 from esben/master

Fixes to problems found with Codacy static analysis