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

Nathaniel Smith njs at pobox.com
Thu Oct 29 13:30:42 EDT 2015 
On Oct 29, 2015 10:22 AM, "Brett Cannon" <brett at python.org> wrote:
>
>
>
> On Thu, 29 Oct 2015 at 09:00 Laura Creighton <lac at openend.se> wrote:
>>
>>
>> see the following:
>> lac at smartwheels:~/junk$ echo "print ('hello there')" >string.py
>> lac at smartwheels:~/junk$ idle-python3.5
>> hello there
>> Traceback (most recent call last):
>>   File "<string>", line 1, in <module>
>>   File "/usr/lib/python3.5/idlelib/run.py", line 10, in <module>
>>     from idlelib import CallTips
>>   File "/usr/lib/python3.5/idlelib/CallTips.py", line 16, in <module>
>>     from idlelib.HyperParser import HyperParser
>>   File "/usr/lib/python3.5/idlelib/HyperParser.py", line 14, in <module>
>>     _ASCII_ID_CHARS = frozenset(string.ascii_letters + string.digits +
"_")
>> AttributeError: module 'string' has no attribute 'ascii_letters'
>>
>> IDLE then produces a popup that says:
>>
>> IDLE's subprocess didn't make connection.  Either IDLE can't stat a
subprocess por personal firewall software is blocking the connection. <ok>
>>
>> --------
>>
>> I think that life would be a whole lot easier for people if instead we
got
>> a message:
>>
>> Warning: local file /u/lac/junk/string.py shadows module named string in
the
>> Standard Library
>>
>> I think that it is python exec that would have to do this -- though of
>> course the popup could also warn about shadowing in general, instead of
>> sending people on wild goose chases over their firewalls.
>>
>> Would this be hard to do?
>
>
> It would require a custom importer or overriding __import__ but it's
doable.

Is there any reason not to issue such warnings by default in the standard
importer? The issue of accidentally shadowing stdlib modules isn't
restricted to idle, it's difficult for idle to handle correctly (how do you
define a custom importer if you don't yet have access to the stdlib?), and
it's not like there's any legitimate reason to want string.py in the
working directory to auto-monkeypatch stdlib string.

(I know saying that last part out loud will probably just cause someone to
pop out of the woodwork and explain how shadowing the sys module is a great
idea and they do it all the time or whatever, but I guess I'll take that
risk :-).)

-n
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