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inspect.getsource() on sourceless dataclass raises undocumented exception

mthuurne

Bug report

If I run the following program in Python 3.10:

from dataclasses import dataclass
from inspect import getsource

defs = {}
exec(
    """
@dataclass
class C:
    "The source for this class cannot be located."
""",
    {"dataclass": dataclass},
    defs,
)

try:
    getsource(defs["C"])
except OSError:
    print("Got the documented exception.")

The output is:

$ python sourceless_dataclass.py 
Traceback (most recent call last):
  File "<path>/sourceless_dataclass.py", line 16, in <module>
    getsource(defs["C"])
  File "/usr/lib/python3.10/inspect.py", line 1147, in getsource
    lines, lnum = getsourcelines(object)
  File "/usr/lib/python3.10/inspect.py", line 1129, in getsourcelines
    lines, lnum = findsource(object)
  File "/usr/lib/python3.10/inspect.py", line 940, in findsource
    file = getsourcefile(object)
  File "/usr/lib/python3.10/inspect.py", line 817, in getsourcefile
    filename = getfile(object)
  File "/usr/lib/python3.10/inspect.py", line 786, in getfile
    raise TypeError('{!r} is a built-in class'.format(object))
TypeError: <class 'C'> is a built-in class

The documentation states that OSError can be raised but does not mention TypeError.

The implementation of inspect.getsource() assumes that if a class has no __module__ attribute, it must be a built-in class, but a sourceless dataclass doesn't have a __module__ attribute either. I don't know whether this is a bug in getsource() or whether the generation of the dataclass should set __module__ to '__main__', but in any case the behavior is not as documented.

Your environment

  • CPython versions tested on: Python 3.10.6
  • Operating system and architecture: Ubuntu Linux 18.04

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