[Python-ideas] Restitute imp.load_source or equivalent in Python 3?

[Brett Cannon]

On Mon Dec 08 2014 at 6:13:45 AM Mart Sõmermaa <mrts.pydev at gmail.com> wrote:

> http://bugs.python.org/issue14551 discusses the deprecation and removal
> of imp.load_source. In the discussion, there seems to be a general
> consensus that (1) a convenience function for loading modules from an
> arbitrary file is a good thing and (2) that many people use it.
>
> I can only concur, the need for loading a module from an arbitrary file
> without having to worry about sys.path or __init__.py is useful for
> supporting plugin-like extensibility/configurability and I personally use
> imp.load_source in a couple of projects.
>
> However, the discussions in http://bugs.python.org/issue14551 seemed to
> have died off without any clear decision for action.
>
> Can we consider adding such a convenience function to importlib in Python
> 3?
>

You have to realize that imp.load_source() has been fundamentally broken
since PEP 302 and just has gotten more broken since Python 3 and importlib.
A correct replacement for imp.load_source() in Python 3.5 would be::

  # Normally a finder would get you the loader and spec.
  loader = importlib.machinery.SourceFileLoader(module_name, path)
  spec = importlib.machinery.ModuleSpec(module_name, loader, origin=path)
  # Basically what import does when there is no loader.create_module().
  module = importlib.util.module_from_spec(spec)
  # Now is the time to put the module in sys.modules if you want.
  # How import initializes the module.
  loader.exec_module(module)

As you can see it's not as simple as "read some bytes from a file and make
an initialized module" which is why imp.load_source() is deprecated. Plus
this side-steps any and all finder and loaders that may be installed which
people want to have executed instead of this recipe. So I don't really want
to promote people side-stepping all of this through the stdlib. Now if
people want to do this in there own code then that's fine and I'm sure
someone has/will create a project on PyPI to implement their own solution.
But at least for importlib I would rather keep it as-is and lower-level and
let the community come up with their own solutions for simplifying the
loading of source code dynamically if they are going to side-step a huge
chunk of the import machinery to do it.
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