Wouldn't a better approach be a way to customize the type of the module? That would allow people to define behavior for almost anything (__call__, __getattr__, __setattr__, __dir__, various operators etc). This question shouldn't exist "why can't I customize behavior X in a module when I can do it for a class". Why go half-way. Thanks, -- Ionel Cristian Mărieș, http://blog.ionelmc.ro On Sun, Sep 10, 2017 at 9:48 PM, Ivan Levkivskyi <levkivskyi@gmail.com> wrote:
I have written a short PEP as a complement/alternative to PEP 549. I will be grateful for comments and suggestions. The PEP should appear online soon.
-- Ivan
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PEP: 562 Title: Module __getattr__ Author: Ivan Levkivskyi <levkivskyi@gmail.com> Status: Draft Type: Standards Track Content-Type: text/x-rst Created: 09-Sep-2017 Python-Version: 3.7 Post-History: 09-Sep-2017
Abstract ========
It is proposed to support ``__getattr__`` function defined on modules to provide basic customization of module attribute access.
Rationale =========
It is sometimes convenient to customize or otherwise have control over access to module attributes. A typical example is managing deprecation warnings. Typical workarounds are assigning ``__class__`` of a module object to a custom subclass of ``types.ModuleType`` or substituting ``sys.modules`` item with a custom wrapper instance. It would be convenient to simplify this procedure by recognizing ``__getattr__`` defined directly in a module that would act like a normal ``__getattr__`` method, except that it will be defined on module *instances*. For example::
# lib.py
from warnings import warn
deprecated_names = ["old_function", ...]
def _deprecated_old_function(arg, other): ...
def __getattr__(name): if name in deprecated_names: warn(f"{name} is deprecated", DeprecationWarning) return globals()[f"_deprecated_{name}"] raise AttributeError(f"module {__name__} has no attribute {name}")
# main.py
from lib import old_function # Works, but emits the warning
There is a related proposal PEP 549 that proposes to support instance properties for a similar functionality. The difference is this PEP proposes a faster and simpler mechanism, but provides more basic customization. An additional motivation for this proposal is that PEP 484 already defines the use of module ``__getattr__`` for this purpose in Python stub files, see [1]_.
Specification =============
The ``__getattr__`` function at the module level should accept one argument which is a name of an attribute and return the computed value or raise an ``AttributeError``::
def __getattr__(name: str) -> Any: ...
This function will be called only if ``name`` is not found in the module through the normal attribute lookup.
The reference implementation for this PEP can be found in [2]_.
Backwards compatibility and impact on performance =================================================
This PEP may break code that uses module level (global) name ``__getattr__``. The performance implications of this PEP are minimal, since ``__getattr__`` is called only for missing attributes.
References ==========
.. [1] PEP 484 section about ``__getattr__`` in stub files (https://www.python.org/dev/peps/pep-0484/#stub-files)
.. [2] The reference implementation (https://github.com/ilevkivskyi/cpython/pull/3/files)
Copyright =========
This document has been placed in the public domain.
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