[Python-ideas] Policy for altering sys.path

[Chris Angelico]

On Thu, May 7, 2015 at 2:07 PM, Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 7 May 2015 at 01:11, Chris Angelico <rosuav at gmail.com> wrote:
>> On Thu, May 7, 2015 at 12:05 AM, Thomas Güttler
>> <guettliml at thomas-guettler.de> wrote:
>>> We run a custom sub class of list in sys.path. We set it in sitecustomize.py
>>>
>>> This instance get replace by a common list in lines like this:
>>>
>>> sys.path = glob.glob(os.path.join(WHEEL_DIR, "*.whl")) + sys.path
>>
>> Forgive the obtuse question, but wouldn't an __radd__ method resolve
>> this for you?
>
> If the custom subclass is implemented in Python or otherwise
> implements the C level nb_add slot, yes, if it's implemented in C and
> only provides sq_concat without nb_add, no (courtesy of
> http://bugs.python.org/issue11477, which gets the operand precedence
> dance wrong for sequence types that only implement the sequence
> methods and not the corresponding numeric ones)

Okay, so it mightn't be quite as simple as I thought, but it should
still be in the control of the author of the subclass, right? That
ought to be easier than trying to stop everyone else from mutating
sys.path.

ChrisA