[New-bugs-announce] [issue16740] Types created with PyType_FromSpec lack a __module__ attribute.

[Bradley Froehle]

New submission from Bradley Froehle:

Types created using PyType_FromSpec do not have a __module__ attribute by default.  This caught me off guard.

$ python3
Python 3.2.3 (default, Oct 19 2012, 20:10:41) 
[GCC 4.6.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import xxlimited
>>> xxlimited.Null.__module__
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: __module__

Do we expect module authors to set the __module__ attribute immediately after calling PyType_FromSpec?

To refresh your memory, non-heap types determine the module/name combo according to something like::

    try:
        __module__, __name__ = tp_name.rsplit('.', 1)
    except ValueError:
        __module__, __name__ = 'builtins', tp_name 

whereas heap types use something like::

    __name__ = tp_name
    @property
    def __module__(self):
        return self.__dict__['__module__']

I think this is unnecessarily confusing, and, as far as I know, not documented anywhere.

I see from reading the commit logs that it was felt that by allowing users to set __name__ (and therefore tp_name), it could have an unintended impact on the value __module__.  If so, why didn't we just disallow setting __name__?

There are likely some unintended impacts of this decision, for example weird error message in other library functions:

>>> import inspect
>>> inspect.getfile(xxlimited.Null)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python3.2/inspect.py", line 415, in getfile
    object = sys.modules.get(object.__module__)
AttributeError: __module__

Is there anything we can do here?

----------
components: Interpreter Core
messages: 177860
nosy: bfroehle
priority: normal
severity: normal
status: open
title: Types created with PyType_FromSpec lack a __module__ attribute.
type: behavior
versions: Python 3.2, Python 3.3, Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16740>
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