[GRASS-dev] os.remove

[Paulo van Breugel]

On Sat, Mar 26, 2016 at 7:21 PM, Glynn Clements <glynn at gclements.plus.com>
wrote:

>
> Paulo van Breugel wrote:
>
> > > In the addon r.forestfrag (python script), I used os.remove() to
> > > remove some temporary files (in lines 230, 258 and 430). However, this
> > > fails in Windows, with an error message like below:
> > >
> > > WindowsError: [Error 32] The process cannot access the file because it
> > > is being used by another process:
> > > 'c:\\users\\uqdshana\\appdata\\local\\temp\\tmpwlv54l'
> > >
> > > Removing these lines with os.remove() solves the problem, but than the
> > > user is left with these temporary files. Is there a Window compatible
> > > way to remove them in the script?
> >
> > Perhaps I should have looked harder first, the underlying problem
> > (described here: https://www.logilab.org/blogentry/17873) seems to be
> > that the file needs to be closed at OS level, which can be done using
> > os.close().
>
> Ideally, files should be handled using context managers and "with".
>
> Python's own file objects are already context managers, so you can use
> e.g.
>
>         with open(filename) as f:
>             data = f.read()
>         # by this point, f has already been closed
>
> For dealing with OS-level descriptors, you can use contextlib (Python
> 2.5+) to easily create context managers, e.g.
>
>         import os
>         import tempfile
>         from contextlib import contextmanager
>
>         @contextmanager
>         def temp():
>             fd, filename = tempfile.mkstemp()
>             try:
>                 yield (fd, filename)
>             finally:
>                 os.close(fd)
>                 os.remove(filename)
>
>         if __name__ == '__main__':      ...
>             with temp() as (fd, filename):
>                 whatever()
>             # fd has been closed and the file removed
>
> Use of "with" ensures that clean-up happens in the event of an
> exception or other forms of early exit (e.g. return, break, continue).
>

Thanks Glynn.. very helpful (but I have to admit that I will need to study
this more carefully to get to understand it all).


>
> --
> Glynn Clements <glynn at gclements.plus.com>
>
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