PyImport_Import Module/embedding: surprising behaviors

[David Abrahams]

I'm seeing highly surprising (and different!) behaviors of
PyImport_Import Module on Linux and Windows when used in a program with
python embedding.

On Linux, when attempting to import a module xxx that's in the current
directory, I get

ImportError: No module named xxx

I can work around the problem by setting

PYTHONPATH=.

On Windows, I get:

'import site' failed; use -v for traceback

I can work around the problem by setting PYTHONPATH to point to the
python library directory:

set PYTHONPATH=c:\P ython25\Lib

I was under the impression that both the current directory *and* the
python library directory were already, automatically, in sys.path, so
I'm really surprised to see this. Am I doing something wrong, or is
this simply the expected behavior (and if so, where is it documented)?

--
Dave Abrahams
Boost Consulting
www.boost-consulting.com

[Aahz]

In article <ma************ *************** ************@py thon.org>,
David Abrahams <da**@boost-consulting.comw rote:

>
I was under the impression that both the current directory *and* the
python library directory were already, automatically, in sys.path, so
I'm really surprised to see this. Am I doing something wrong, or is
this simply the expected behavior (and if so, where is it documented)?

IIRC (without bother to test), there has been some change in the
definition of "current directory" -- it used to be the actual current
directory of os.getcwd(), but since changed to the startup directory.
--
Aahz (aa**@pythoncra ft.com) <* http://www.pythoncraft.com/

"Typing is cheap. Thinking is expensive." --Roy Smith

[Alex Martelli]

Aahz <aa**@pythoncra ft.comwrote:

In article <ma************ *************** ************@py thon.org>,
David Abrahams <da**@boost-consulting.comw rote:

I was under the impression that both the current directory *and* the
python library directory were already, automatically, in sys.path, so
I'm really surprised to see this. Am I doing something wrong, or is
this simply the expected behavior (and if so, where is it documented)?

IIRC (without bother to test), there has been some change in the
definition of "current directory" -- it used to be the actual current
directory of os.getcwd(), but since changed to the startup directory.

In 2.3 and later, at least (sorry, no 2.2 and earlier around to check),
site.py makes every directory along sys.path an absolute path at Python
startup. This _should_ probably be documented at
<http://docs.python.org/lib/module-site.html>, but it doesn't appear to
be clearly stated there (the page only speaks of site's job of
"appending site specific paths", and not of the other jobs it also
performs, such as normalizing sys.path by turning all paths into
absolute ones and removing duplicates).
Alex

[Ziga Seilnacht]

David Abrahams wrote:

I'm seeing highly surprising (and different!) behaviors of
PyImport_Import Module on Linux and Windows when used in a program with
python embedding.

On Linux, when attempting to import a module xxx that's in the current
directory, I get

ImportError: No module named xxx

I can work around the problem by setting

PYTHONPATH=.

Python puts the current directory in sys.path only if it can't
determine the directory of the main script. There was a bug on
Windows that always added current directory to sys.path, but it
was fixed in Python 2.5. This is documented in the library
reference:

http://docs.python.org/lib/module-sys.html#l2h-5149

On Windows, I get:

'import site' failed; use -v for traceback

I can work around the problem by setting PYTHONPATH to point to the
python library directory:

set PYTHONPATH=c:\P ython25\Lib

This happens because Python calculates the initial import path by
looking for an executable file named "python" along PATH. You can
change this by calling Py_SetProgramNa me(filename) before calling
Py_Initialize() . This is documented in API reference manual:

http://docs.python.org/api/embedding.html

That page also describes a few hooks that you can overwrite to
modify the initial search path. They are described in more detail
on this page:

http://docs.python.org/api/initialization.html

HTH,
Ziga

[David Abrahams]