[Tutor] __init__.py question

[Marilyn Davis]

Thank you for your careful explanation, Steven.

I guess there's nothing more for me to know.

While I think it is a mistake to put directories in your package directory
structure that aren't part of the package, that seems to be all it's
about.

Well, I guess I don't feel quite so stupid.

Thank you folks.

Marilyn Davis


On Wed, June 1, 2011 5:11 pm, Steven D'Aprano wrote:

> Marilyn Davis wrote:
> [...]
>
>> There's something I'm missing because I think you simply can't call
>> something string.py unless you are willing to give up the library
>> string.py.
>
> No, you're right about that. Python's search path is "first match wins".
> Whether it's a package or a module, it will match before the library
> string.py. Adding __init__.py doesn't change that.
>
> (Unless you re-arrange sys.path so that library modules come first.)
>
>
> However, you can have a directory called "string", containing arbitrary
> .py files. So you could drop this in your path:
>
>
>
> string/ +-- a.py
> +-- b.py
>
>
> and add string to the path so that the directory is searched, and still
> get the standard string.py. (I haven't actually tried this, but it should
> work.)
>
> Only if you put a file __init__.py into the directory will it shadow the
> standard library string.py.
>
> Personally, I think the emphasis given in the docs about shadowing
> standard library files is misplaced. I think that is actually irrelevant. I
> think a more useful explanation for the need for __init__.py is simple:
> how else could Python distinguish a package from a mere directory
> containing Python files?
>
> A mere directory is not searched unless it is explicitly added to the
> path; a mere directory cannot be imported. A package can be. But since a
> package *is* a directory at the file system level, how should Python
> distinguish them?
>
> I suppose Python could have the rule "the directory must end in .py to
> be considered a package". But then, when you import the main package
> instead of a submodule, which file should Python read? There needs to be a
> standard naming convention for the file to be treated as the top-level
> module. But since you have such a file, there's no longer any need for
> adding a .py to the end of the directory name, since the standard file is
> sufficient to determine that the directory is a package.
>
> That file could have been called anything, __init__.py was chosen by
> analogy with __init__ methods in classes and because it's unlikely to clash
> with any name package authors might choose for their own use.
>
>
>
> --
> Steven
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