Import mechanism to support multiple Python versions

[Nicolas Fleury]

Hi,
I'm trying to support two Python versions at the same time and I'm
trying to find effective mechanisms to support modules compiled in C++
transparently.

All my code in under a single package. Is it possible to override the
import mechanism only for modules under that package and sub-packages so
that?:

import cppmymodule

would be equivalent to:

if sys.version == "2.4":
import cppmymodule24 as cppmymodule
elif sys.version == "2.3":
import cppmymodule23 as cppmymodule

for all modules under the package and all modules with names beginning
with cpp (or another way to identify them).


I have also third party packages. Is it possible to make a package
point to another folder? For example:

psyco23/...
psyco24/...
psyco/__init__.py => points to psyco23 or psyco24 depending on Python
version used.

Note that I cannot use .pth files or symbolic links, since I would want
the exact same code hierarchy to work with both Python 2.3 and 2.4.

Any help appreciated.
Thx and regards,
Nicolas

[Thomas Heller]

Re: Import mechanism to support multiple Python versions

Nicolas Fleury <nid_oizo@yahoo .com_remove_the _> writes:
[color=blue]
> I have also third party packages. Is it possible to make a package
> point to another folder? For example:
>
> psyco23/...
> psyco24/...
> psyco/__init__.py => points to psyco23 or psyco24 depending on Python
> version used.[/color]

You may manipulate the package path in the __init__.py file.
pkgutil may also be useful.

Thomas

[Nicolas Fleury]

Re: Import mechanism to support multiple Python versions

Nicolas Fleury wrote:[color=blue]
> import cppmymodule
>
> would be equivalent to:
>
> if sys.version == "2.4":
> import cppmymodule24 as cppmymodule
> elif sys.version == "2.3":
> import cppmymodule23 as cppmymodule
>
> for all modules under the package and all modules with names beginning
> with cpp (or another way to identify them).[/color]

Since all my imports are absolute, my code looks more like:

import root.subpackage .cppmymodule

So I guess, I can add this in root/__init__.py and everything would be fine:

def myimport(name, globals=None, locals=None, fromlist=None,
__import__=__im port__):
names = name.split('.')
if names[0] == 'root' and names[-1][0:3] == 'cpp':
name += '%s%s' % sys.version_inf o[0:2]
return __import__(name , globals, locals, fromlist)

__builtins__['__import__'] = myimport

It seems to work, is that right?

Thx and regards,
Nicolas

[Serge Orlov]

Re: Import mechanism to support multiple Python versions

Nicolas Fleury wrote:[color=blue]
> Hi,
> I'm trying to support two Python versions at the same time and I'm
> trying to find effective mechanisms to support modules compiled in
> C++ transparently.
>
> All my code in under a single package. Is it possible to override
> the import mechanism only for modules under that package and
> sub-packages so that?:
>
> import cppmymodule
>
> would be equivalent to:
>
> if sys.version == "2.4":
> import cppmymodule24 as cppmymodule
> elif sys.version == "2.3":
> import cppmymodule23 as cppmymodule
>
> for all modules under the package and all modules with names
> beginning with cpp (or another way to identify them).[/color]

I used the following approach application-wide:
===== The very start of main file ===
resolve_package _dependencies()
import package

def main():
...

# boilerplate at the end of main file
def resolve_package _dependencies() :
if sys.version_inf o[0:2] == (2,5):
import package1
sys.modules["package"] = sys.modules["package1"]
else:
import package2
sys.modules["package"] = sys.modules["package2"]

=============== =============== =======

I've never needed that for packages like you, but as far as I
remember package specific modules are stored like
"package.module " so aliasing "package45" with "package" in your
case will look like
sys.modules[__name__+".pack age"] = sys.modules[__name__+".pack age45"]

Serge.

[Greg Ewing]

Re: Import mechanism to support multiple Python versions

Nicolas Fleury wrote:[color=blue]
> All my code in under a single package. Is it possible to override the
> import mechanism only for modules under that package and sub-packages so
> that?:[/color]

Yes. A package module has a __path__ attribute to which
you can add additional directories to be searched for
submodules of that package. So in your package's
__init__.py you can do something like

if sys.version == "2.4":
subdir = "python24"
elif sys.version == "2.3":
subdir = "python23"

__path__.append (os.path.join(o s.path.basename (__file__, subdir)))

The directory structure is then

yourpackage/
__init__.py
python23/
cppmymodule.pyd (2.3 version)
python24/
cppmymodule.pyd (2.4 version)

but at run time it will appear as though one version or
the other of cppmymodule is a direct submodule of
yourpackage.

--
Greg Ewing, Computer Science Dept,
University of Canterbury,
Christchurch, New Zealand

http://www.cosc.canterbury.ac.nz/~greg