Implicit namespace package is not linted if it is inside a regular package

[cl0ne]

Steps to reproduce

1. Create implicit namespace package inside regular package, for example:

   $ tree package_with_namespace
   package_with_namespace
   ├── __init__.py
   └── namespace
       └── module.py
   
   1 directory, 2 files

2. Create similar hierarchy when a top-level namespace package contains a regular package with its own namespace package inside, for example:

   $ tree namespace
   namespace
   ├── outer_module.py
   └── package
       ├── __init__.py
       ├── innerspace
       │   ├── inner_module.py
       │   └── inner_package
       │       └── __init__.py
       └── package_module.py
   
   3 directories, 5 files

3. Put show_warning = True (or something similar) into .py files just to get some warnings.
4. Run pylint on package_with_namespace, package_with_namespace.namespace and package_with_namespace.namespace.module
5. Run pylint on namespace

Current behavior

$ pylint package_with_namespace
************* Module package_with_namespace
package_with_namespace/__init__.py:1:0: C0114: Missing module docstring (missing-module-docstring)
package_with_namespace/__init__.py:1:0: C0103: Constant name "show_warning" doesn't conform to UPPER_CASE naming style (invalid-name)

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$ pylint package_with_namespace.namespace
$ pylint package_with_namespace.namespace.module
************* Module package_with_namespace.namespace.module
package_with_namespace/namespace/module.py:1:0: C0114: Missing module docstring (missing-module-docstring)
package_with_namespace/namespace/module.py:1:0: C0103: Constant name "show_warning" doesn't conform to UPPER_CASE naming style (invalid-name)

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$ pylint namespace
************* Module namespace.outer_module
namespace/outer_module.py:1:0: C0114: Missing module docstring (missing-module-docstring)
namespace/outer_module.py:1:0: C0103: Constant name "show_warning" doesn't conform to UPPER_CASE naming style (invalid-name)
************* Module namespace.package.package_module
namespace/package/package_module.py:1:0: C0114: Missing module docstring (missing-module-docstring)
namespace/package/package_module.py:1:0: C0103: Constant name "show_warning" doesn't conform to UPPER_CASE naming style (invalid-name)
************* Module namespace.package
namespace/package/__init__.py:1:0: C0114: Missing module docstring (missing-module-docstring)
namespace/package/__init__.py:1:0: C0103: Constant name "show_warning" doesn't conform to UPPER_CASE naming style (invalid-name)
************* Module namespace.package.innerspace.inner_module
namespace/package/innerspace/inner_module.py:1:0: C0114: Missing module docstring (missing-module-docstring)
namespace/package/innerspace/inner_module.py:1:0: C0103: Constant name "show_warning" doesn't conform to UPPER_CASE naming style (invalid-name)
************* Module namespace.package.innerspace.inner_package
namespace/package/innerspace/inner_package/__init__.py:1:0: C0114: Missing module docstring (missing-module-docstring)
namespace/package/innerspace/inner_package/__init__.py:1:0: C0103: Constant name "show_warning" doesn't conform to UPPER_CASE naming style (invalid-name)

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Expected behavior

Output from pylint package_with_namespace and pylint package_with_namespace.namespace should contain output from pylint package_with_namespace.namespace.module just like with pylint namespace.

pylint --version output

pylint 2.6.0
astroid 2.4.2
Python 3.8.6 (default, Sep 30 2020, 04:00:38) 
[GCC 10.2.0]

[dbaty]

package_with_namespace/namespace/__init__.py is missing. If I add it, errors in package_with_namespace/namespace/module.py are correctly detected by Pylint.

Python may be able to cope with the absence of __init__.py [1], but pylint does not. I think it's a feature and I would suggest adding missing __init__.py everywhere they are needed.

[1] The Python tutorial says the file is required, though:

The init.py files are required to make Python treat directories containing the file as packages.

[cl0ne]

package_with_namespace/namespace/__init__.py is missing.

I would suggest adding missing __init__.py everywhere they are needed.

Nope, that is intended and conforms to namespace package definition. I named that sub-package namespace to emphasize that it is a namespace package, not a regular one.

[1] The Python tutorial says the file is required, though:

The init.py files are required to make Python treat directories containing the file as packages.

PEP420 has clarifications on this matter, though:

Regular packages will continue to have an __init__.py and will reside in a single directory.
Namespace packages cannot contain an __init__.py.

[dbaty]

Thanks for the links, I did not know about namespace packages. I'll go back studying the subject and let others chime in. :)

[bdegreve]

Nope, that is intended and conforms to namespace package definition. I named that sub-package namespace to emphasize that it is a namespace package, not a regular on

I'm not finding anything in PEP420 that forbids this, but isn't it kind of moot for namespace.package.innerspace to be a namespace? After all, namespace.package can only exist in one space in the filesystem, and thus also namespace.package.innerspace? I.e. you can't split namespace.package.innerspace in two different installations.

I'm asking this, because I was just wondering about this myself ...

[cl0ne]

I'd admit that the second example is made-up, kind of "what if" experiment. And in real world situations it probably doesn't have a lot of sense.

[DanielNoord]

As a note to self, this will not be fixed with #6405 and requires further investigation.