New submission from Tzu-ping Chung <uranu...@gmail.com>:
While trying to migrate pip’s internal usages of distutils to sysconfig,[1] I
noticed there isn’t a way for pip to select a scheme for sysconfig.get_paths()
for `pip install --target` and `pip install --user`. I tried to implement some
logic to "guess" a scheme ("posix_home" for `--home`, "nt_user" for `--user`
when os.name is "nt", etc.), but eventually hit a wall trying to support
alternative implementations.
PyPy, for example, adds additional schemes "pypy" and "pypy_nt", and it’s not
clear whether pip should use then for `--home` or not. @mattip helped clear
this up for PyPy (which also prompts bpo-43307), but we are worried that other
implementations may introduce even more special rules that causes problems, and
it’s also not a good idea for pip to implement special logic for every
implementation.
I would propose two changes to sysconfig:
1. Make sysconfig._get_default_scheme() a public function. This function will
be documented for implementations to return a default scheme to use when none
is given to sysconfig.get_paths().
2. Add a new function sysconfig.get_preferred_schemes() for implementations to
return preferred schemes for prefix, home, and user installations. This
function should return a dict[str, str] with three keys "prefix", "home", and
"user", and their values the scheme names to use.
I would be happy to work on a PR and iterate on the design if this sounds like
a reasonable idea. For CPython, the implementation would be something like (to
match distutils’s behaviour):
def get_preferred_schemes():
if os.name == "nt":
return {
"prefix": "nt",
"home": "posix_home",
"user": "nt_user",
}
return {
"prefix": "posix_prefix",
"home": "posix_home",
"user": "posix_user",
}
[1]: https://github.com/pypa/pip/pull/9626
----------
components: Library (Lib)
messages: 387611
nosy: uranusjr
priority: normal
severity: normal
status: open
title: Interface to select preferred "user" or "home" sysconfig scheme for an
environment
versions: Python 3.10
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue43312>
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