On 15.09.2021 21:02, Guido van Rossum wrote:
> To make chdir() return a context manager *and* keep it working without calling
> `__enter__`, it would have to call `getcwd()`, which I've heard is expensive.
>
> So I don't think that would work, alas.
At least on Linux, the cost for os.getcwd() is similar to the cost
of os.chdir(), but yes, since we can't have os.chdir() not change
the dir when called, the logic would need the extra os.getcwd() call:
# python3 -m timeit -s 'import os' "os.getcwd()"
500000 loops, best of 5: 619 nsec per loop
# python3 -m timeit -s 'import os' "os.chdir('.')"
500000 loops, best of 5: 726 nsec per loop
Here's simple implementation of the chdir() context manager:
import os
import pathlib
# chdir context manager
PlatformPath = pathlib.WindowsPath if os.name == 'nt' else pathlib.PosixPath
class chdir(PlatformPath):
def __init__(self, dir):
self.dir = dir
self.olddir = os.getcwd()
os.chdir(dir)
def __enter__(self):
return self
def __exit__(self, *exc):
os.chdir(self.olddir)
return False
# Normal chdir()
path = chdir('abc/')
print (os.getcwd())
print (path.olddir)
# chdir() context manager
with chdir('def/') as wd:
print (repr(wd))
print (os.getcwd())
print (os.listdir('.'))
For extra perks, I made os.chdir() return a pathlib Path object
and you get to see the old directory, so you can backtrack
if needed, even without a context manager.
> On Wed, Sep 15, 2021 at 11:55 AM Eric V. Smith <e...@trueblade.com
> <mailto:e...@trueblade.com>> wrote:
>
> On 9/15/2021 2:48 PM, Eric Fahlgren wrote:
>> On Wed, Sep 15, 2021 at 12:21 AM Eric V. Smith <e...@trueblade.com
>> <mailto:e...@trueblade.com>> wrote:
>>
>> And I'm not crazy about the name "workdir". To me, it sounds like it
>> returns something, not sets and resets something. But I don't have a
>> particularly great alternative in mind: in my own code I've used
>> "change_dir", which isn't awesome either.
>>
>>
>> Our version is named "pushdir", modeled after shell's pushd (even though
>> pushdir is a context manager and does auto-pop). Everyone figures out
>> what it does at a glance.
>
> That's a great name!
>
> Although I think having os.chdir() return a context manager is a better
> design (assuming it can work, but at first blush it would seem so).
>
> Eric
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