inspect.getsource only works for objects loaded from files, not interactive session

[PCManticore]

BPO	12920
Nosy	@terryjreedy, @ned-deily, @merwok, @bitdancer, @PCManticore, @Naddiseo, @BlckKnght, @native-api, @vmsp, @Ark-kun

^{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 = None
created_at = <Date 2011-09-06.18:37:57.848>
labels = ['interpreter-core', '3.8', 'expert-IDLE', 'type-bug', '3.7']
title = 'inspect.getsource only works for objects loaded from files, not interactive session'
updated_at = <Date 2020-11-30.02:13:01.074>
user = 'https://github.com/PCManticore'

bugs.python.org fields:

activity = <Date 2020-11-30.02:13:01.074>
actor = 'Ark-kun'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['IDLE', 'Interpreter Core']
creation = <Date 2011-09-06.18:37:57.848>
creator = 'Claudiu.Popa'
dependencies = []
files = []
hgrepos = []
issue_num = 12920
keywords = []
message_count = 15.0
messages = ['143645', '143773', '143790', '143831', '185179', '245714', '245721', '245723', '252846', '265815', '297768', '297797', '328836', '331659', '382107']
nosy_count = 12.0
nosy_names = ['terry.reedy', 'ned.deily', 'eric.araujo', 'r.david.murray', 'Claudiu.Popa', 'Naddiseo', 'Steven.Barker', 'Ivan.Pozdeev', 'zorceta', 'nikitakit', 'vmsp', 'Ark-kun']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'needs patch'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue12920'
versions = ['Python 3.7', 'Python 3.8']

Linked PRs

• gh-57129: Add test for inspect.getsource in the REPL #111197

[PCManticore]

inspect.getsource called with a class defined in the same file fails with
TypeError: <module '__main__' (built-in)> is a built-in class, although the documentation says that:

"The argument may be a module, class, method, function, traceback, frame,
or code object. The source code is returned as a single string." I think that should be specified in documentation that this function works only for objects living in a module.

[merwok]

inspect.getsource called with a class defined in the same file fails
with TypeError: <module '__main__' (built-in)> is a built-in class

The error message makes me think that getsource(__main__) was used, not getsource(SomeClass). Can you check again?

[PCManticore]

Yes. On Python 3.2 (r32:88445, Feb 20 2011, 21:29:02) [MSC v.1500 32 bit (Intel)] on win32, the result for the following lines:

import inspect
class A:
    pass
inspect.getsource(A)

is:

Traceback (most recent call last):
  File "E:/Scripts/Snippets/test_inspect_bug.py", line 4, in <module>
    inspect.getsource(A)
  File "C:\Python32\lib\inspect.py", line 694, in getsource
    lines, lnum = getsourcelines(object)
  File "C:\Python32\lib\inspect.py", line 683, in getsourcelines
    lines, lnum = findsource(object)
  File "C:\Python32\lib\inspect.py", line 522, in findsource
    file = getsourcefile(object)
  File "C:\Python32\lib\inspect.py", line 441, in getsourcefile
    filename = getfile(object)
  File "C:\Python32\lib\inspect.py", line 406, in getfile
    raise TypeError('{!r} is a built-in class'.format(object))
TypeError: <module '__main__' (built-in)> is a built-in class
>>>

[PCManticore]

I forgot to mention that I executed this code directly in IDLE. It seems to work perfectly on command line though.

[merwok]

It seems to work perfectly on command line though.

If the code is saved in a file, yes, but not in an interactive interpreter. This is not actually related to IDLE, but to the fact that inspect.getsource merely finds the __file__ attribute of the module object for its argument. If a module object has no file, the error message indicates that it’s a built-in module (like sys), but this fails to take into account the special __main__ module in an interactive interpreter.

It might be worth it to improve the error message, and in any case the documentation can be improved.

[ned-deily]

In duplicate bpo-24491, zorceta notes: "Both python.exe and IDLE can't. IPython is able to, as it inserts REPL input into linecache."

[zorceta]

When provided object is not from a file, like input in interactive shell, inspect internals will check for it in linecache, which official Python shell and IDLE won't put interactive shell input into, yet. This can be simply solved.

Whether interactive shell input can be put into linecache may be a problem, but it'll make life easier, as interactive shell saves time from edit-save-run 'loop'.

btw, I changed the title, since I don't think, what original author thought need to be documented, is absolutely right.