[issue37519] Three inconsistent module attributes

[Eric V. Smith]

Eric V. Smith  added the comment:

While some of these might be inconsistent (I haven't really looked at it 
thoroughly yet), I think it might be problematic to change them at this point, 
since there's no doubt code out there that depends on the current behavior.

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[issue37519] Three inconsistent module attributes

[Brett Cannon]

Change by Brett Cannon :


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[issue37519] Three inconsistent module attributes

[Géry]

Change by Géry :


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[issue37519] Three inconsistent module attributes

[Géry]

Géry  added the comment:

@Brett Cannon

> PEPs actually become historical documents once they are implemented

Actually the inconsistency of the values of the 3 module attributes 
(``__file__``, ``__cached__`` and ``__package__``) is with respect to the other 
values within the current implementation (not only with respect to the values 
specified in PEP 451). Sorry if I did not explain this well. Let me detail:

For ``__file__``, if you look at the current output of the above "Imported 
modules" section, you have:

- __file__: None, for an imported namespace package;
- __file__: 'not set', for an imported built-in module;
- __file__: 'not set', for an imported frozen module,

which is inconsistent: it should always be 'not set' when ``__file__`` has no 
meaning.

For ``__cached__``, if you look at the current output of the above "Run 
modules" section, you have:

- __cached__: None, for a non-package module run from the file system 
(``python3 module.py``) or run from standard input (``cat module.py | 
python3``);
- __path__: 'not set', for a non-package module run from the file system 
(``python3 module.py``) or run from standard input (``cat module.py | 
python3``),

which is inconsistent: it should always be 'not set' when ``__cached__`` has no 
meaning, like it is already the case for ``__path__`` and other module 
attributes.

For ``__package__``, if you look at the current output of the above "Run 
modules" section, you have:

- __package__: None, for a non-package module run from the file system 
(``python3 module.py``) or run from standard input (``cat module.py | 
python3``);
- __package__: '', for a non-package module run from the module namespace 
(``python3 -m module``) or a package run from the file system (``python3 
module/``).

which is inconsistent: it should always be ``''`` when there is no parent 
package for ``__package__`` to refer to.

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[issue37519] Three inconsistent module attributes

[Brett Cannon]

Brett Cannon  added the comment:

PEPs actually become historical documents once they are implemented, so could 
you please check what the official docs say in regards to this to see if there 
is an inconsistency in the semantics?

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[issue37519] Three inconsistent module attributes

[Géry]

New submission from Géry :

Analysis


In the next two sections showing the module attributes and corresponding spec 
attributes of imported modules and run modules, we notice the following rule 
(which is in accordance with this `PEP 451 section 
`_):

If a *spec* attribute is either ``None``, ``'built-in'`` or ``'frozen'``, 
then the corresponding *module* attribute is not set.

However we also notice three exceptions to this rule, that I think are 
unintended inconsistencies that should be corrected:

- ``module.__file__ is None`` (instead of being not set) for imported namespace 
packages;
- ``module.__cached__ is None`` (instead of being not set) for non-package 
modules run from the file system and run from standard input;
- ``module.__package__ is None`` (instead of being ``''``) for non-package 
modules run from the file system and run from standard input.

The first exception was introduced recently (26 February 2018) by this `pull 
request `_, which changed the 
``module.__spec__.origin`` attribute from ``namespace`` to ``None`` (which I 
agree with as it avoids conflicting non-namespace-package modules named 
``namespace`` with namespace packages) and the ``module.__file__`` attribute 
from being unset to ``None`` (which I disagree with as it introduces an 
inconsistency and contradicts PEP 451).

Environment: CPython 3.7, MacOS 10.14.


Imported modules


Running the following code::

import module

print("MODULE")

for attr in ["__name__", "__file__", "__cached__", "__path__", 
"__package__", "__loader__"]:
print(f"{attr}:", repr(getattr(module, attr, "not set")))

print("SPEC")

if hasattr(module, "__spec__"):
if module.__spec__ is None:
print("__spec__:", repr(module.__spec__))
else:
for attr in ["name", "origin", "cached", 
"submodule_search_locations", "parent", "loader"]:
print(f"__spec__.{attr}:", repr(getattr(module.__spec__, attr)))
else:
print("__spec__: not set")

where ``module`` refers to:

- a non-package module (e.g., ``pathlib``);
- a regular package (e.g., ``json``);
- a namespace package;
- a built-in module (e.g., ``time``);
- a frozen module (e.g., ``_frozen_importlib_external``)

prints the following module attributes and corresponding spec attributes of the 
imported ``module``:

- for a non-package module:

| MODULE
| __name__: 'pathlib'
| __file__: 
'/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pathlib.py'
| __cached__: 
'/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/__pycache__/pathlib.cpython-37.pyc'
| __path__: 'not set'
| __package__: ''
| __loader__: <_frozen_importlib_external.SourceFileLoader object at 
0x1018896d8>
| SPEC
| __spec__.name: 'pathlib'
| __spec__.origin: 
'/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/pathlib.py'
| __spec__.cached: 
'/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/__pycache__/pathlib.cpython-37.pyc'
| __spec__.submodule_search_locations: None
| __spec__.parent: ''
| __spec__.loader: <_frozen_importlib_external.SourceFileLoader object at 
0x1018896d8>

- for a regular package:

| MODULE
| __name__: 'json'
| __file__: 
'/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/__init__.py'
| __cached__: 
'/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/__pycache__/__init__.cpython-37.pyc'
| __path__: 
['/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json']
| __package__: 'json'
| __loader__: <_frozen_importlib_external.SourceFileLoader object at 
0x10f9aa6d8>
| SPEC
| __spec__.name: 'json'
| __spec__.origin: 
'/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/__init__.py'
| __spec__.cached: 
'/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/__pycache__/__init__.cpython-37.pyc'
| __spec__.submodule_search_locations: 
['/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json']
| __spec__.parent: 'json'
| __spec__.loader: <_frozen_importlib_external.SourceFileLoader object at 
0x10f9aa6d8>

- for a namespace package:

| MODULE
| __name__: 'foobar'
| __file__: None
| __cached__: 'not set'
| __path__: _NamespacePath(['/Users/maggyero/foobar'])
| __package__: 'foobar'
| __loader__: <_frozen_importlib_external._NamespaceLoader object at 
0x1074564a8>
| SPEC
| __spec__.name: 'foobar'
| __spec__.origin: None
| __spec__.cached: None
| __spec__.submodule_search_locations: 
_NamespacePath(['/Users/maggyero/foobar'])
| __spec__.parent: 'foobar'
| __spec__.loader: <_frozen_importlib_external._NamespaceLoader object at 
0x1074564a8>

- for a buil