import from user input? What about 'from'?

[Christian Tismer]

Chad Netzer wrote:
> Christian Tismer wrote:
> 
> > Instead, one should cut off the first name before the first dot
> > and put that into globals().
> >
> > import string
> > globals()[string.split(modname, ".")[0]] = __import__(modname)
> >
> > seems to do it better.
> 
> Hmm, what if I want to do something like:
> 
> exec 'from ' + module_name + ' import ' + class_name
> 
> Can I use the __import__call, and then just save the specific module name in globals()?
> ie. (minus exception checking):
> 
>     globals()[class_name] = getattr(__import__(module_name), class_name)

Yes, this is ok with a single module and a single object in the
module. But for a full

from package.subpackage.module import object

you need to read the description of __import__ in section 2.3 of the 
Python Library Reference and do a bit more.

Using the full __import__ syntax of
__import__ (name[, globals[, locals[, fromlist]]]) 

import package.subpackage.module

must be handled in a way that "package" goes into your module,
but "subpackage" gets imported into "package", and
"module" gets imported into "subpackage".
WHich means, our handle's name to be put into globals
is "package". On the other hand, for a

from package.subpackage.module import object

we need to work downhill from "package" to "module" and
pick the attribute "object", and we don't insert any
module into globals.

Example:

>>> target = "constants"
>>> modname = "win32com.client"
>>> fromlist = ["client"]
>>> glob = globals()
>>> loc=locals()
>>> glob[target] = getattr(__import__(modname, glob, loc, fromlist), target)
>>> constants
<win32com.client.Constants instance at 1608e50>
>>> 

This the exact equivalent of
from win32com.client import constants

Please don't ask me why fromlist has to be a list, dunno.
But its non-emptiness makes __import__ return the last,
not the first element in pi.pa.po .

To get the full idea what happens, I'd further read the module
knee.py, which is a description what happens internally today.
Maybe someone can explain the details of fromlist to me  :-)

ciao - chris

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