import module from package - confusing syntax

[David MacQuigg]

I'm setting up a large hierarchy of module packages and using a
variable to select which of many alternative packages to import. For
example, the variable 'config.modsel' points to a particular "model
selector" package. 'config' is a module containing many such
variables.

My first attempt resulted in a confusing error message:
[color=blue][color=green][color=darkred]
>>> from config.modsel.m odelselector import ModelSelector[/color][/color][/color]

Traceback (most recent call last):
File "<pyshell#2 5>", line 1, in -toplevel-
from config.modsel.m odelselector import ModelSelector
ImportError: No module named modsel.modelsel ector

It works if I enter the literal path rather than a variable:
[color=blue][color=green][color=darkred]
>>> config.modsel[/color][/color][/color]
<module 'libs.modsel01' ... >[color=blue][color=green][color=darkred]
>>> from libs.modsel01.m odelselector import ModelSelector
>>> ModelSelector[/color][/color][/color]
<class libs.modsel01.m odelselector.Mo delSelector at 0x009F68D0>

I need to use a variable, however. The best I can come up with is:
[color=blue][color=green][color=darkred]
>>> exec('from '+ config.modsel._ _name__ +'.modelselecto r import ModelSelector')
>>>[/color][/color][/color]

Is this the best we can do with current Python syntax?

Should we think about suggesting a better syntax? I think the
fundamental problem is the confusion that arises from using '.' as
both a path separator and an attribute qualifier.

-- Dave

[Mark McEahern]

Re: import module from package - confusing syntax

On Sat, 2004-07-03 at 08:21, David MacQuigg wrote:[color=blue]
> I'm setting up a large hierarchy of module packages and using a
> variable to select which of many alternative packages to import.[/color]

This means you need __import__.

// m

[David MacQuigg]

Re: import module from package - confusing syntax

On Sat, 03 Jul 2004 08:54:50 -0500, Mark McEahern
<marklists@mcea hern.com> wrote:
[color=blue]
>On Sat, 2004-07-03 at 08:21, David MacQuigg wrote:[color=green]
>> I'm setting up a large hierarchy of module packages and using a
>> variable to select which of many alternative packages to import.[/color]
>
>This means you need __import__.[/color]

__import__ looks even messier than exec() We have to interpolate the
string 'config.modsel' twice.

import libs, config
config.modsel = 'modsel01'

## # What we want:
## from (config.modsel) .modelselector import ModelSelector

## # Works, but messy:
## __import__('lib s.%s.modelselec tor' % config.modsel)
## modsel = getattr(libs, config.modsel)
## ModelSelector = modsel.modelsel ector.ModelSele ctor

# Still seems like the lesser evil:
exec('from libs.%s.modelse lector import ModelSelector' %
config.modsel)

The __import__ function looks like a real kludge. There is a
suggestion in section 2.1 of the Library Reference to use the 'imp'
module, and write my own import function. I guess I'll look at that
next.

-- Dave