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.

> 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?

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
>>>

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

> 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.

In duplicate Issue24491, zorceta notes: "Both python.exe and IDLE can't. IPython is able to, as it inserts REPL input into linecache."

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.

> When provided object is not from a file

should be

'When `inspect` can't find the source file of provided object'.

My mistake.

I just ran into this issue trying to introspect an IPython session, in which case the __main__ module doesn't have a file associated with it.

But it turns out that methods defined in a class do have source code associated with them, so it's possible to add a workaround for the common case where a class actually has methods.

Code: https://gist.github.com/nikitakit/642cb96febdf2f812d0b

The problem being discussed here just came up on Stack Overflow today: http://stackoverflow.com/questions/37288135/inspect-module-for-python/

The cause of the incorrect error message is pretty clear. The relevant code from `inspect.getfile` should do something better when the object has a `__module__` attribute, but the module named (when looked up in `sys.modules`) does not have a `__file__` attribute. Currently it says the module is a builtin class, which is total nonsense.

A very basic fix would be to have an extra error case:

    if isclass(object):
        if hasattr(object, '__module__'):
            object = sys.modules.get(object.__module__)
            if hasattr(object, '__file__'):
                return object.__file__
            raise TypeError()              # need a relevant message here!!!
        raise TypeError('{!r} is a built-in class'.format(object))

It might be easier to make a meaningful message if the code after the first `if` didn't overwrite `object` with the module.

But, really, it would be nice to figure out a better fix, which would make the relevant inspect functions actually work for classes defined interactively in the `__main__` module.

So, what would be the right approach here? Store the interactive session's input text in memory?

Probably.  Figure out a protocol to inject them into linecache, perhaps.  But I'm not sure such a thing would be accepted.  If you can figure out a way to make it work at least theoretically, it would probably be best to talk about it on python-ideas first.

In the meantime it would be nice to improve the error message, which is what we should use this issue for.

See https://bugs.python.org/issue33826?@ok_message=msg%20328824%20created%0Aissue%2033826%20message_count%2C%20messages%20edited%20ok&@template=item#msg319692 how IPython stores source from interactive input and why it's not appropriate for vanilla REPL IMO.

Do we really need to say that getsource(object) can only get the object's source if it is accessible from the object?  Getsource also fails if a module is loaded from a .pyc with not corresponding .py available.

The problem is not the call being in __main__.  When I put the three lines (with the 3rd wrapped with print()) in an IDLE editor and run, and re-inspect, I get

======================== RESTART: F:\Python\a\tem3.py ========================
class A:
    pass

>>> inspect.getsource(A)
'class A:\n    pass\n'

Ditto if I run > py -i -m a.tem3

If I continue in IDLE's Shell

>>> class B: pass

>>> inspect.getsource(B)
Traceback (most recent call last):
  File "<pyshell#3>", line 1, in <module>
    inspect.getsource(B)
  File "F:\dev\37\lib\inspect.py", line 973, in getsource
    lines, lnum = getsourcelines(object)
  File "F:\dev\37\lib\inspect.py", line 955, in getsourcelines
    lines, lnum = findsource(object)
  File "F:\dev\37\lib\inspect.py", line 812, in findsource
    raise OSError('could not find class definition')
OSError: could not find class definition

If I enter the three lines above in a fress python or IDLEs shell, I get the TypeError above.

IDLE does store interactive inputs into linecache, so that tracebacks contain the offending line (unlike interactive python). But it does so on a statement by statement basis, so that each entry is treated as a separate file.  In a traceback for an exception in a multiline statement, the line number is relative to the statement.

>>> def f():
	# line2 of f
	1/0

	
>>> f()
Traceback (most recent call last):
  File "<pyshell#13>", line 1, in <module>
    f()
  File "<pyshell#12>", line 3, in f
    1/0
ZeroDivisionError: division by zero

Interactive python displays '<stdin>' as the file for all entries.  IDLE numbers them, so previous statements remained cached.  I consider enhanced interactive tracebacks to be an important feature.

But I don't see how to attach individual pseudofile names to classes and functions so that getsource could find their source lines.

This is also an issue even for non-interactive scenarios:

When doing `python -c '<some code>'` inspect.getsource does not work and there are no stack traces.

Perhaps this case will be easier to fix?