[Python-3000] Chaning the import machinery; was: Re: [Python-Dev] setuptools in 2.5.

[Walter Dörwald]

Guido van Rossum wrote:

> On 4/20/06, Walter Dörwald <walter at livinglogic.de> wrote:
>> I'd like to be able to simply import a file if I have the filename. And
>> I'd like to be able to load sourcecode from an Oracle database and have
>> useful "filename" and line number information if I get a traceback.
> 
> Great use cases. Could I ask you to elaborate these in the Python-3000
> list? It would be very useful if you attempted to specify what
> (approximately) the API for these would look like and how it would
> work (e.g. the immediate question with import from a file or URL is
> what happens if another module imports the same thing).

Maybe import should become a function (maybe even a generic function ;))
so we can do:

cStringIO = import(url("file:/usr/local/lib/python2.5/cStringIO"))

import cx_Oracle
db = cx_Oracle.connect("...")

mymodule = import(oraclesource(db=db, query="select source from modules
where name='mymodule'"))

code = """
cache = 1000
color = True
"""

options = import(literal(code))

Simple imports could look like this:
urllib2 = import("urllib2")

(i.e. pass the module name as a string). Unfortunately this means that
the module name has to be specified twice.

All objects passed to import() should be usable as dictionary keys, so
that they can be stored as keys in sys.modules which would continue to
be the module cache.

In a traceback the repr() of this object should be displayed (maybe with
the exception of import("urllib2") which should display the real filename).

So far this means that we would have to get rid of relative imports.
Another option would be to make a relative import be the responsibility
of the module to which the import is relative.

Even better would be if import() would do some kind of dependency
tracking during import for modules that are recursively imported during
import of the original module. Then

mymodule = reload(oraclesource(db=db, query="select source from modules
where name='mymodule'")

could do the right thing (i.e. import the module if it's not in
sys.modules or it has changed since the last import or one of the
modules it uses has changed; otherwise use the cached module). This
would mean that each import resource would have to provide some kind of
cookie (a checksum or a timestamp), so that it's possible to detect if
the source has changed (and of course it needs a method to return the
real source code string).

I've implemented something like this once, but abandoned the idea
because tracebacks simply have "<string>" as the filename, and that
makes debugging a PITA. Anyway the source code for this is here:

http://styx.livinglogic.de/~walter/pythonimport/resload.py

Servus,
   Walter