New submission from Andrew Barnert:
The documentation and implementation for `inspect.isbuiltin` and related
functions do not match. While #4968 attempted to clarify things to make the
documentation match the behavior, the actual committed changes are still wrong.
`isbuiltin` says "Return true if the object is a built-in function or a bound
built-in method", but it returns false for bound built-in special methods
(e.g., `[].__add__`). That's because it's implemented as
`isinstance(types.BuiltinFunctionType)`, but bound special methods are a
different type (`method-wrapper`). Terry Reedy's suggested fix from #4968 ("...
or a bound built-in non-special method") would fix this, but the committed
change didn't.
The docstring has a further problem; it says that anything that passes will
have a `__self__` with "instance to which a method is bound, or None", but for
functions, the `__self__` is usually the module the `PyMethodDef` comes from,
not `None`. (For example, `sum.__self__` is the`'builtins` module.)
`isroutine` says "Return true if the object is a user-defined or built-in
function or method." (The docstring instead says "… any kind of function or
method.") But it returns false for built-in bound special methods
(`[].__add__`). That's because it's implemented as `isbuiltin` or `isfunction`
or `ismethod` or `ismethoddescriptor`; while `isbuiltin` picks up functions and
bound non-special methods, and `ismethoddescriptor` picks up unbound special
and non-special methods, nothing picks up bound special methods.
A doc-only fix for this, along with Terry's suggested fix for `isbuiltin`,
would be "Return true if the object is a user-defined function or method, or a
built-in function, unbound method, or bound non-special method." That sounds
horrible, but that's because it actually is a horrible test in the first place.
A better fix would be to make `isbuiltin` handle both kinds of bound method.
Then `isroutine` is correct as written, and both are documented correctly.
(Note that there is no type in `types` corresponding to `method-wrapper`, so
either `types` or `inspect` would have to add something like
`BuiltinSpecialMethodType = type([].__add__)`.)
It would be even better to fix this at the source and clean up the types of
builtin functions and methods, but that boat sailed with 3.0, so...
----------
assignee: docs@python
components: Documentation
messages: 236649
nosy: abarnert, docs@python
priority: normal
severity: normal
status: open
title: isbuiltin, isroutine, etc.
versions: Python 3.4, Python 3.5
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue23525>
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