changing sys.path

Andrea Crotti andrea.crotti.0 at
Thu Feb 2 05:03:42 EST 2012

On 02/02/2012 12:51 AM, Steven D'Aprano wrote:
> On Wed, 01 Feb 2012 17:47:22 +0000, Andrea Crotti wrote:
>> Yes they are exactly the same, because in that file I just write exactly
>> the same list,
>> but when modifying it at run-time it doesn't work, while if at the
>> application start
>> there is this file everything works correctly...
>> That's what really puzzles me.. What could that be then?
> Are you using IDLE or WingIDE or some other IDE which may not be
> honouring sys.path? If so, that's a BAD bug in the IDE.
> Are you changing the working directory manually, by calling os.chdir? If
> so, that could be interfering with the import somehow. It shouldn't, but
> you never know...
> Are you adding absolute paths or relative paths?

No, no and absolute paths..

> You say that you get an ImportError, but that covers a lot of things
> going wrong. Here's a story. Could it be correct? I can't tell because
> you haven't posted the traceback.
> When you set site-packages/my_paths.pth you get a sys path that looks
> like ['a', 'b', 'fe', 'fi', 'fo', 'fum']. You then call "import spam"
> which locates b/ and everything works.
> But when you call sys.path.extend(['a', 'b']) you get a path that looks
> like ['fe', 'fi', 'fo', 'fum', 'a', 'b']. Calling "import spam" locates
> some left over junk file, fi/ or fi/spam.pyc, which doesn't
> import, and you get an ImportError.
And no the problem is not that I already checked inspecting at run-time..
This is the traceback and it might be related to the fact that it runs 
from the
.exe wrapper generated by setuptools:

Traceback (most recent call last):
   File "c:\python25\scripts\", line 8, in <module>
     load_entry_point('psi.devsonly==0.1', 'console_scripts', 'dev_main')()
   File "h:\git_projs\psi\psi.devsonly\psi\devsonly\bin\", 
line 152, in main
   File "h:\git_projs\psi\psi.devsonly\psi\devsonly\bin\", 
line 86, in full_run
     run(project_name, test_only=self.ns.test_only)
   File "h:\git_projs\psi\psi.devsonly\psi\devsonly\", 
line 277, in run
     from import Runner
   File "h:\git_projs\psi\psi.devsonly\psi\devsonly\", line 7, in 
     from psi.workbench.api import Workbench, set_new_dev_main
ImportError: No module named workbench.api

Another thing which might matter is that I'm launching Envisage 
applications, which
heavily rely on the use of entry points, so I guess that if something is 
not in the path
the entry point is not loaded automatically (but it can be forced I 
guess somehow).

I solved in another way now, since I also need to keep a dev_main.pth in 
to make Eclipse happy, just respawning the same process on ImportError works
already perfectly..

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