Brett Cannon added the comment:
The impetus of ModuleNotFoundError is the need for something similar in
importlib thanks to ``from ... import``. When you do something like
__import__('os', fromlist=['path']), any ImportError must be silenced **if** it
relates only to the fact that the module can't be found. Other errors directly
related to technical errors which also raised ImportError are supposed to
propagate.
Before ModuleNotFoundError I was setting a made-up attribute called _not_found
on ImportError and then raising the exception. I could then catch the exception
and introspect for that case as necessary. See
http://hg.python.org/cpython/file/3e10025346c1/Lib/importlib/_bootstrap.py for
the last revision that contained _not_found.
Since I had a legitimate case of wanting to differentiate between ImportError
(which represents both technical errors and an inability to find a module) and
the more specific case of simply not finding a module, I decided to formalize
the distinction. It made sense to me so that the old try/except ImportError
trick to ignore missing module could not accidentally catch the technical error
use of ImportError by accident and mask the problem.
Now if you still think the subclass is not worth it then I probably need a
better solution than a faked private attribute on ImportError to delineate the
technical error/module not found difference as I had already received one bug
report asking to define what _not_found was. ImportError could grow a not_found
attribute formally or even a 'reason' attribute which could be set to some enum
value representing the fact the exception was triggered because the module
simply wasn't found (although that seems unnecessary and more like errno from
OSError).
To summarize, the options I see are:
1. Back to _not_found on ImportError (only existed to start with as it was too
late in 3.3 to come up with a better solution)
2. Keep ModuleNotFoundError (this option can include reverting all of the
``except ImportError`` changes I made and just allow the exception to exist if
you want)
3. Add a not_found attribute to ImportError more formally (defaults to None for
undefined, set to True/False to clearly signal when an obvious answer is known)
4. Add a 'reason' attribute that can be set to an enum which has a value which
represents "module not found"
I can't easily make it a private exception that I prevent from escaping
importlib thanks to trying to allow the accelerated version of import to use
importlib's fromlist code (see how _handle_fromlist is called with its import_
argument).
----------
_______________________________________
Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue15767>
_______________________________________
_______________________________________________
Python-bugs-list mailing list
Unsubscribe:
http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
