This comes from this thread in the Python Ar­genti­na mail­ing list (which I strong­ly rec­om­mend if you read span­ish).

I was the oth­er day try­ing to do shel­l-scrip­t-­like-things on python (as part of a mon­ster set­up.py) and I was an­noyed that in shell it's easy to do this:

cd foo
bar -baz
cd -

Or this:

pushd foo
bar -baz
popd

Or this:

(cd foo && bar -baz)

And on Python I had to do this, which is ver­bose and ug­ly:

cwd = os.getcwd()
try:
    os.chdir('foo')
    os.system('bar -baz')
finally:
    os.chdir(cwd)

This is what I want­ed to have:

with os.chdir('foo'):
    os.system('bar -baz')

And of course, you can't do that. So, I asked, how do you im­ple­ment that con­text man­ager? I got sev­er­al an­swer­s.

1. That's avail­able in Fab­ric:

   with cd("­foo"):
       run("bar")

2. It's not hard to do:

   class DirCon­textM(ob­jec­t):
       def __init__(­self, new_dir):
           self­.new_dir = new_dir
           self­.old_dir = None
   
       def __en­ter__(­self):
           self­.old_dir = os­.getcwd()
           os­.chdir(­self.new_dir)
   
       def __ex­it__(­self, *_):
           os­.chdir(­self.old_dir)

3. It's even eas­i­er to do:

   from con­textlib im­port con­textman­ag­er
   
   @con­textman­ag­er
   def cd(­path):
       old_dir = os­.getcwd()
       os­.chdir(­path)
       yield
       os­.chdir(old_dir)

4. That's cool, so let's add it to path.py

5. Maybe check for ex­­cep­­tions

   @con­textman­ag­er
   def cd(­path):
       old_dir = os­.getcwd()
       os­.chdir(­path)
       try:
           yield
       fi­nal­ly:
           os­.chdir(old_dir)

All in al­l, I learned how to do con­text man­ager­s, about con­textlib, about fab­ric and about path.py. Which is not bad for 15 min­utes :-)