Inspect.getsource raises wrong error on classes in interactive session

[akulakov]

BPO	44648
Nosy	@jaraco, @aroberge, @ambv, @pablogsal, @miss-islington, @FFY00, @akulakov
PRs	bpo-44648: Fix error type in inspect.getsource() in interactive session #27171 [3.10] bpo-44648: Fix error type in inspect.getsource() in interactive session (GH-27171) #27495 bpo-44771: rename namespacedata01 to namespacedata #27484 bpo-44771: Apply changes from importlib_resources 5.2.1 #27436

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = None
closed_at = <Date 2021-07-30.17:47:14.167>
created_at = <Date 2021-07-15.18:31:38.611>
labels = ['type-bug', '3.10', '3.11']
title = 'Inspect.getsource raises wrong error on classes in interactive session'
updated_at = <Date 2021-08-02.09:59:39.832>
user = 'https://github.com/akulakov'

bugs.python.org fields:

activity = <Date 2021-08-02.09:59:39.832>
actor = 'pablogsal'
assignee = 'none'
closed = True
closed_date = <Date 2021-07-30.17:47:14.167>
closer = 'lukasz.langa'
components = []
creation = <Date 2021-07-15.18:31:38.611>
creator = 'andrei.avk'
dependencies = []
files = []
hgrepos = []
issue_num = 44648
keywords = ['patch']
message_count = 11.0
messages = ['397573', '397629', '397631', '397634', '397636', '398579', '398580', '398588', '398589', '398590', '398748']
nosy_count = 8.0
nosy_names = ['jaraco', 'aroberge', 'lukasz.langa', 'pablogsal', 'miss-islington', 'FFY00', 'andrei.avk', 'othmaneelbouri1']
pr_nums = ['27171', '27495', '27484', '27436']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue44648'
versions = ['Python 3.10', 'Python 3.11']

[akulakov]

[ins] In [63]: class A:pass

[ins] In [64]: import inspect

[ins] In [65]: inspect.getsource(A)

[snip]

/usr/local/Cellar/python@3.9/3.9.1/Frameworks/Python.framework/Versions/3.9/lib/python3.9/inspect.py in getfile(object)
664 if getattr(module, '__file__', None):
665 return module.__file__
--> 666 raise TypeError('{!r} is a built-in class'.format(object))

The error is 'X is a built-in class', instead it should be OSError, source code is not available.

[ambv]

Why do you think OSError fits here? Since objects provided on the command line by definition cannot have source code files, the problem isn't that the file is missing or inaccessible. Rather, the value provided to getsource() is wrong. So, in my view, this should rather be ValueError.

Moreover, checking for __main__ is insufficient as there are __main__.py modules after all in many packages.

[akulakov]

Łukasz:

Thanks for looking at this!

• I agree OSError is not ideal, but I chose it because it's consistent with how inspect reports similar errors. For example, see all instances of OSError, except for first, in this function:

cpython/Lib/inspect.py

Line 930 in 7915c96

def findsource(object):

I think it's an implementation detail that class source is not available on interactive prompt, for example function source is available via inspect.getsource().

If a user can do getsource(func) and getsource(cls) in a file, and getsource(func) on interactive prompt, it seems wrong to return a ValueError when the user is trying to getsource(cls) in interactive.

I'm open to change it to ValueError though because I think the err message here is more important to avoid user confusion.

• good point about __main__.py files, I didn't remember about them. However they will have the __file__ attribute set, so they will return that right above the check for '__main__' in my patch.

I tested it to make sure:
import inspect
class A: 0
print(inspect.getsource(A))

./python.exe ~/temp/main.py
class A: 0

[akulakov]

I'm not sure though how is the unit test succeeding since the test module should have __file__ set. Looking into it..

[akulakov]

This is kind of interesting:

• The unit test was wrong, it was catching the wrong OSError. (I was catching regex first but after some tweaking and changes I lost it and forgot to readd)

• The reason it was passing is exactly what you pointed out -- the main.py in unittest package. After I change the class' module to main in the test, it starts looking at sys.modules['main'] which is the one in unittest, which doesn't have this class, which causes the inspect to throw another OSError.

• I fixed the unit test by both checking for error regex and patching sys.modules['__main__'] (and of course restoring it later).

Thanks for helping to catch this :-)

[ambv]

New changeset 48a6255 by andrei kulakov in branch 'main':
bpo-44648: Fix error type in inspect.getsource() in interactive session (GH-27171)
48a6255

[ambv]

Since this is an exception type change, I'd feel more comfortable leaving 3.9 out of the backports here. That way it will be easier for application authors to differentiate between when the change was introduced or not.