Avoid use of sys.version to obtain Python version

[svisser]

This change converts use of sys.version to sys.version_info as sys.version is not guaranteed to contain the version number at the beginning of the string across Python implementations (see also the note at https://docs.python.org/2/library/sys.html#sys.version).

[foutaise]

Hi @svisser,

Good catch! Thanks for your PR.

Regards,

[svisser]

Thanks for merging it in!