change a file with a context manager

[Andrea Crotti]

On 12/13/2011 10:59 AM, Andrea Crotti wrote:
> So I have the following problem, I need something to copy a file to a 
> certain position
> and restore it after.
> So I wrote this simple context manager:
>
> class WithCorrectEasyInstall(object):
>
>     def __enter__(self):
>         import pkg_resources
>         from shutil import copyfile
>         easy_install_file = 
> pkg_resources.resource_filename('psi.devsonly', 
> 'windows_easy_install.pth')
>         self.global_easy_install = 
> 'c:/python25/Lib/site-packages/easy-install.pth'
>         # can use mmap, a temporary file or just write to string
>         self.stored = open(self.global_easy_install).read()
>         logger.debug("copying the correct easy_install.pth file to the 
> global position")
>         copyfile(easy_install_file, self.global_easy_install)
>
>     def __exit__(self, type, value, traceback):
>         #TODO: make sure it's restored also when quitting in some 
> other ways
>         # restore the old file
>         open(self.global_easy_install, 'w').write(self.stored)
>         logger.debug("restoring the old easy_install.pth file")
>
>
> The problem is that this is not executed for example when the program 
> is interrupted
> with for example a KeyboardInterrupt.
> But that's also an exception, why is it not caught by the context 
> manager?
>
> And if there are better way to do what I'm trying to achieve they are 
> welcome :)


Alright it was probably a stupid idea to start with.
The problem is that if the easy_install is wrong even the imports in the 
module
will not work, so I can't even start to do something.

Another possible option is to just add to the path everything contained 
in that
correct easy_install.pth file.
Or is there a way to reload the path settings?