[issue42032] Setting PYTHONPYCACHEPREFIX using ~ (tilde) creates a "~" folder

[Petr Viktorin]

Petr Viktorin  added the comment:

> It would perhaps be useful if the os.path.expanduser call was added in the 
> cache_from_source() function in importlib?

No: that would mean Python would be doing work that the shell should do. 
Possibly it would be duplicating the work. Possibly it would be doing it wrong. 
What if your shell uses ⌂ rather than ~? What if the shell has a different idea 
of what the home directory is? Remember, you can use Python with any shell, not 
just Unix/POSIX command-line ones (which is what os.path.expanduser emulates).

Thanks for reporting the issue, though! The separation of concerns definitely 
isn't obvious at first.

--
nosy: +petr.viktorin
resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue42032] Setting PYTHONPYCACHEPREFIX using ~ (tilde) creates a "~" folder

[Veronica Olsen]

Veronica Olsen  added the comment:

> AFAIK, tilde expansion is entirely up to your shell rather than Python

Yes, I am uncertain what exactly is going on here. Whatever ends up in the 
sys.pycache_prefix variable is different with the same environment variable 
setting on the two systems. It may simply be an OS quirk. I am running on 
Debian testing after all.

It is clear from the CPython source that Python does nothing with the tilde. It 
eventually calls os.makedirs() in the compile() function, which I guess is when 
my tilde folder was made.

It would perhaps be useful if the os.path.expanduser call was added in the 
cache_from_source() function in importlib?

As for the results from the debug checks:

1)
Debian: GNU bash, version 5.0.18(1)-release (x86_64-pc-linux-gnu)
Ubuntu: GNU bash, version 5.0.17(1)-release (x86_64-pc-linux-gnu)

2)
They both expand ~ to the home folder

3)
They both return ~/test

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[issue42032] Setting PYTHONPYCACHEPREFIX using ~ (tilde) creates a "~" folder

[Zachary Ware]

Zachary Ware  added the comment:

AFAIK, tilde expansion is entirely up to your shell rather than Python (unless 
you use something like `os.path.expanduser` in your own program).

A few debugging questions:
1) What version of what shell(s) do you have on each system?

2) What value do you get from `TESTVAR=~/test python3 -c 'import 
os;print(os.environ["TESTVAR"])'` on each system?  Is it the same as 
`TESTVAR=~/test printenv | grep TESTVAR`?

3) What results do you get from the same tests as above, but with 
`TESTVAR='~/test'`?

--
nosy: +zach.ware

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[issue42032] Setting PYTHONPYCACHEPREFIX using ~ (tilde) creates a "~" folder

[Veronica Olsen]

Veronica Olsen  added the comment:

Correction: The pycache is in fact redirected to the new '~' folder.

In any case, I tested a bit on Debian Bullseye (Python 3.8.6) and Ubuntu 20.04 
(Python 3.8.5) and it seems ~ is not expanded in the environment variable 
Debian. I'm a little uncertain what is the expected behaviour here, but the 
sys.pycache_prefix variable returns different results on the two platforms:

With environment variable set to ~/.pycache on 3.8.6 (on debian testing), I get 
the following:

Python 3.8.6 (default, Sep 25 2020, 09:36:53) 
[GCC 10.2.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.pycache_prefix
'~/.pycache'
>>> 

Doing the same on 3.8.5 on ubuntu 20.04 produces:

Python 3.8.5 (default, Jul 28 2020, 12:59:40) 
[GCC 9.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.pycache_prefix
'/home/**/.pycache'
>>> 

Still, perhaps the pycache_prefix should expand the ~ on linux?

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[issue42032] Setting PYTHONPYCACHEPREFIX using ~ (tilde) creates a "~" folder

[Veronica Olsen]

New submission from Veronica Olsen :

On Debian Bullseye (testing):

Setting

export PYTHONPYCACHEPREFIX=~/.pycache

has previously worked. With Python 3.8.6, this still works in practice, when 
running python code (the pycache is still redirected), but during 
initialisation, the python3 executable creates an empty folder named "~" in the 
folder where the python exec or a python script is run.

Changing the environment variable to:

export PYTHONPYCACHEPREFIX=$HOME/.pycache

resolves the issue.

Expansion of ~ is of course a bit fickly in general, but 

I assume this is not intended. Deleting those folders from command line is 
rather tricky!

--
components: Interpreter Core
messages: 378607
nosy: vkbo
priority: normal
severity: normal
status: open
title: Setting PYTHONPYCACHEPREFIX using ~ (tilde) creates a "~" folder
type: behavior
versions: Python 3.8

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