How to import only one module in a package when the package __init__.py has already imports the modules?

Peng Yu pengyu.ut at gmail.com
Sun Nov 1 04:29:12 CET 2009


On Sat, Oct 31, 2009 at 10:03 PM, Steven D'Aprano
<steve at remove-this-cybersource.com.au> wrote:
> On Sat, 31 Oct 2009 16:53:50 -0500, Peng Yu wrote:
>
>> I know that multiple classes or functions are typically defined in one
>> file (i.e. module in python). However, I feel this make the code not
>> easy to read. Therefore, I insist on one class or function per file (i.e
>> module in python).
>>
>> When one class per module is strictly enforced, there will be no need to
>> have different capitalization conventions for modules and classes.
>> Developers should be able to tell whether it is a class or a module from
>> the context.
>
> Classes and modules are first-class objects in Python, so you can't
> necessarily tell what they are from context. I frequently have code like
> this:
>
>
> def verify(test_func, objects_to_process, expected_results):
>    for obj, result in zip(objects_to_process, expected_results):
>        print "Testing %r..." % obj,
>        r = test_func(obj)
>        if r == result:
>            print "verified"
>        else:
>            print "expected %r but got %s" % (result, r)

This example doesn't invalidate my statement. When I say "Developers
should be able to tell whether it is a class or a module from the
context", I mean the case of defining them or creating objects. In the
above case, you still can enforce one class/function per module.

> objects_to_process could be a list of floats, strings, functions,
> modules, or anything else. Having a naming convention is still useful for
> distinguishing (say) factory functions from classes, or modules from
> classes.
>
>
>> In my question, module A and B exist just for the sake of
>> implementation. Even if I have module A and B, I don't want the user
>> feel the existence of module A and B. I want them feel exact like class
>> A and B are defined in module 'test' instead of feeling two modules A
>> and B are in package 'test'.
>
>
> Inside test/__init__.py:
>
> from A import A  # class A from file A.py
> from B import B  # class B from file B.py

I can not use the above approach as I mentioned its problem in my
previous message.

> or better still:
>
> from a import A  # class A from file a.py
> from b import B  # class B from file b.py

This artificially introduces the constraint that the file name can not
be the same as the class/function name. There is no constraint like
this if I can C++.

>> I know that module names should be in lower
>> cases, in general. However, it is OK to have the module name capitalized
>> in this case since the end users don't see them.
>
> Of course they do.

This sentence is confusing. Can you spell out what you mean?

>> I looked at python library, there are quite a few __init__.py files are
>> not empty. In fact, they are quite long. I agree with you that
>> '__init__.py' should not be long. But I'm wondering why in python
>> library __init__.py are quite long.
>
> Define "quite long".
>
> In Python 2.6, I have:
>
> [steve at sylar python2.6]$ for file in */__init__.py; do echo "$file" `cat
> $file | wc -l` ; done
> bsddb/__init__.py 450
> compiler/__init__.py 29
> ctypes/__init__.py 546
> curses/__init__.py 59
> distutils/__init__.py 26
> email/__init__.py 123
> encodings/__init__.py 157
> hotshot/__init__.py 78
> idlelib/__init__.py 1
> json/__init__.py 318
> lib2to3/__init__.py 1
> logging/__init__.py 1490
> multiprocessing/__init__.py 271
> sqlite3/__init__.py 24
> test/__init__.py 1
> wsgiref/__init__.py 23
> xml/__init__.py 47
>
>
>
> With the exception of logging, I don't see any of those as quite long.

I have defined 'long' in one of my previous message. I consider a file
long, when it does not fit in one or two screen. Basically, I want to
get a whole picture of the file after glancing of the file.



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