[Python-ideas] "Regular" namespace packages

[Dmitry Malinovsky]

Hello,

I'm implementing an extensible library. Along with the library itself I
want to implement various extensions (and some of these extensions will be
also pluggable).

I found that creating a namespace package will be user-friendly (to
distinguish default implementations from third-party ones).
However, current namespace packages implementation does not allow me to
have a dedicated regular package with the same name as the namespace.
E.g. if I have to namespaced packages: top.packageA and top.packageB, I
can't have dedicated top package.
(Actually, I can do that: py module is the example, but this way is not
easy to implement for the library developers and to understand
by external contributors).

So my idea is to have a standard (and easy) way to declare a package which
can act both as a namespace package and a regular package,
like pep-420 (implicit namespace packages) standardized way to create
namespace packages.

Here is an example:

first/first/__init__.py:
X = 1

second/first/second/__init__.py:
Y = 2

import sys
sys.path += ['first', 'second']

import first
first.X  # 1
import first.second  # I expect to get 2,
first.second.Y         # but currently ImportError is raised

If I understand this correctly, this change will require to modify the
default submodule lookup algorithm,
so when the import machinery finds the cached first module, and there is no
second submodule defined,
the machinery launches the standard namespace packages finder algorithm (as
described in [1]),
excluding first package directory from the search path.

>From a user perspective, assuming we have a mature library with lots of
extensions (for example, flask),
and a pluggable extension (like flask-flatpages), the following imports

from flask import Flask
from flask_flatpages import FlatPages
from flask_flatpages_knitr import FlatPagesKnitr

can be rewritten as follows:

from flask import Flask
from flask.flatpages import FlatPages
from flask.flatpages.knitr import FlatPagesKnitr

which I find more readable than the first snippet.

What do you think about it? Is flat better than nested, or namespaces are
really great?

Thank you for any feedback!

[1] https://www.python.org/dev/peps/pep-0420/#dynamic-path-computation

-- 
Dmitry Malinovsky
Senior DevOps
Thumbtack Technology
Email: dmalinovsky at thumbtack.net <pnegoduyko at thumbtack.net>
Skype: d_malinoff
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