[docs] [issue15867] It's hard to decypher how to build off of the provided objects from the importlib docs

[Julian Berman]

New submission from Julian Berman:

I find that the importlib documentation is a bit too low level. Import hooks are not that common, so requiring a bit of reading is OK with me, but I somewhat *understand* PEP 302, so I have a general idea of *what* I want to do and what kind of objects can accomplish that, and still find it hard to figure out how to take the pieces provided by importlib and use them to do what I want.

If I provide a specific example, I want to create a path hook that "just" does the usual import behavior, but before executing the module, does some transformation on the source code, say. In trying to figure out the best way to do that I had a hard time using the docs to figure out which pieces I should assemble to do that. I'm going to just describe the rough series of steps I went through, and hopefully that will help give a picture of where in the docs I had trouble.

`importlib.abc` has a few things that would appear to help. None of the things seem like an exact match, so immediately I'm confused -- after reading PEP 302 I'd have expected to need to find an object to implement one or both of `get_code` or `get_source` on, or one that has that implemented that I can subclass and extend. The closest thing there that I find is PyPycLoader, which seems to be saying it implements the standard import behavior, but the docs say its deprecated and to use SourceLoader. At this point, after checking out `SourceLoader` and seeing that it has me implementing two methods whose purpose I don't quite understand, even after reading the short descriptions of them, at least not in the context of what I want to do, I begin to suspect that what I really want is to combine SourceLoader with some things from the `imp` module, or maybe `importlib.__import__`, but am left wondering again how much I need to implement before I just can use that. I then notice `importlib.util.module_for_loader`, and add that to the simple loader I've written which I'm still waiting to plug `imp` into, before realizing that that decorator eats the `fullname` attribute and *only* passes along the module, which confuses me, since now I don't know how to retrieve the source for the module object that I'm being passed -- so I save the path name in `__init__` for the class, and assume that's what I should be doing, despite not seeing an example doing that. Assuming that's even correct as-is, it took me quite a bit to put those pieces together.

So I apologize for rambling -- I think essentially what'd improve things is providing more examples, or perhaps a HOWTO entry, that targeted assembling the pieces provided in the module into a few clear, complete examples of finders, loaders and importers.

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assignee: docs at python
components: Documentation
messages: 169901
nosy: Julian, docs at python
priority: normal
severity: normal
status: open
title: It's hard to decypher how to build off of the provided objects from the importlib docs
versions: Python 3.3, Python 3.4

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue15867>
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