look further down sys.path for extension module

[Vincent Wehren]

Hi,

Is it possible to have Python look further down sys.path for a C
extension module when an ImportError is raised because of the "dynamic
module not implementing init function"?

The thing is, I have a case where the cwd of an application that embedds
the Python interpreter needs to be inserted into sys.path at index. For
the windows version there is a zlib.dll in the app's directory, which -
naturally - gets "import precedence" over zlib.pyd from the DLLs
directory. For the time being, I place copy zlib.pyd into he app's
directory to solve the problem, but it would be nice if there was a way
to avoid having to do this.


Any thoughts much appreciated.
--
Vincent Wehren

[vincent wehren]

Re: look further down sys.path for extension module

Vincent Wehren wrote:

[...][color=blue]
> the Python interpreter needs to be inserted into sys.path at index.[/color]

This should say "[...] into sys.path at index 0.

--
Vincent Wehren

[Martin v. Löwis]

Re: look further down sys.path for extension module

Vincent Wehren wrote:[color=blue]
> Is it possible to have Python look further down sys.path for a C
> extension module when an ImportError is raised because of the "dynamic
> module not implementing init function"?[/color]

You could use the imp module to import zlib.pyd "manually". Then, when
an "import zlib" occurs, it looks into sys.modules, finds that zlib is
already there, and forgets about looking into sys.path.

Alternatively, you could rebuild zlib.pyd to be named pyzlib.pyd. You
need to rebuild the code because you also need to rename the entry
function, and the name of the module inside the module itself. You
can then do

import pyzlib as zlib

Regards,
Martin

[vincent wehren]

Re: look further down sys.path for extension module

Martin v. Löwis wrote:[color=blue]
> Vincent Wehren wrote:
>[color=green]
>> Is it possible to have Python look further down sys.path for a C
>> extension module when an ImportError is raised because of the "dynamic
>> module not implementing init function"?[/color]
>
>
> You could use the imp module to import zlib.pyd "manually". Then, when
> an "import zlib" occurs, it looks into sys.modules, finds that zlib is
> already there, and forgets about looking into sys.path.[/color]

This sounds like a viable option. We already have some special hooks to
accomodate for using pywin32 from a network install so this would be
something along those same lines.
[color=blue]
> Alternatively, you could rebuild zlib.pyd to be named pyzlib.pyd. You
> need to rebuild the code because you also need to rename the entry
> function, and the name of the module inside the module itself. You
> can then do
>
> import pyzlib as zlib[/color]

Yes, quickly tried that, too. It still is registered in sys.modules as
"pyzlib" - don't known if I expected that...


Thanks for your input!

--
Vincent Wehren

[Alex Martelli]

Re: look further down sys.path for extension module

vincent wehren <vincent@visual trans.de> wrote:
...[color=blue][color=green]
> > Alternatively, you could rebuild zlib.pyd to be named pyzlib.pyd. You
> > need to rebuild the code because you also need to rename the entry
> > function, and the name of the module inside the module itself. You
> > can then do
> >
> > import pyzlib as zlib[/color]
>
> Yes, quickly tried that, too. It still is registered in sys.modules as
> "pyzlib" - don't known if I expected that...[/color]

The merely local renaming should not accidentally cause multiple
repetitions of the module's loading if somewhere else the module gets
simply imported with 'import pyzlib', of course. So, it's recoded in
sys.modules['pyzlib'] -- anything else would be astonishing.

Just add a further statement
sys.modules['zlib'] = zlib
right after this import, if you want future 'import zlib' statements to
get 'redirected' to use the already-imported pyzlib instead.


Alex