how to enforce one version of python

[Wojciech Puchar]

>>  part is the combination of 2-only holdouts and new 3-only code,
>>  which is why it's easy to end up with both installed.
>
> 	_This_ is really annoying.  I try to keep my systems with exactly
> what they need installed, to reduce both bloat and possibly security
> issues.  There's one Perl installation; having two Python versions -
> and trying to keep track between them - makes me use a lot of bad
> language.
>
>
Just another variation of DLL hell. Welcome to modern software environment 
;)