[Python-ideas] [Python-Dev] If you shadow a module in the standard library that IDLE depends on, bad things happen

[Chris Angelico]

On Sun, Nov 1, 2015 at 6:53 PM, Laura Creighton <lac at openend.se> wrote:
> In a message of Sun, 01 Nov 2015 17:06:30 +1100, "Steven D'Aprano" writes:
>
>>I propose the following two changes:
>>
>>
>>(1) Beginning with Python 3.6, the default is that the current directory
>>is put at the end of sys.path rather than the beginning. Instead of:
>>
>>    >>> print(sys.path)
>>    ['', '/this', '/that', '/another']
>>
>>we will have this instead:
>>
>>    >>> print(sys.path)
>>    ['/this', '/that', '/another', '']
>>
>>Those who don't shadow installed packages won't notice any
>>difference.
>>
>>Scripts which deliberately or unintentionally shadow installed packages
>>will break from this change. I don't have a problem with this. You can't
>>fix harmful behaviour without breaking code that depends on that harmful
>>behaviour.
>
> This is a bad idea, if you mean 'shadows anything in site-packages'.
> I write a perfectly good working program, which then silently breaks
> because somebody happens to install a site package with a name
> conflict with my code.  Can you imagine being in the middle of
> writing and debugging such a thing and have everything start
> failing because suddenly your program isn't the one being found?
> How long is it going to take you to stop looking at your own code,
> and your own setup for the problem and begin looking at what
> packages got installed by anybody else sharing this machine, and
> what they are named?

I'm fairly sure Steven's talking about the standard library, not
arbitrary packages people might happen to have installed. Whether he
thought about it or not, the solution to both your problems seems to
be this:

sys.path = ['/usr/local/lib/python36.zip', '/usr/local/lib/python3.6',
'/usr/local/lib/python3.6/plat-linux',
'/usr/local/lib/python3.6/lib-dynload', '',
'/home/rosuav/.local/lib/python3.6/site-packages',
'/usr/local/lib/python3.6/site-packages']

Equivalently, for the system Python:

sys.path = ['/usr/lib/python3.4',
'/usr/lib/python3.4/plat-x86_64-linux-gnu',
'/usr/lib/python3.4/lib-dynload', '',
'/usr/local/lib/python3.4/dist-packages',
'/usr/lib/python3/dist-packages']


So the current directory is after everything that's logically the
standard library, but before things that would be installed separately
(site-packages, dist-packages, etc). It'd no longer be possible to
shadow wave.py, but you could shadow sqlalchemy.py.

ChrisA