command pip list --outdated fails

[Xohwie1i]

Problem description
Running pip list --outdated fails with the following error:

ERROR: Exception:
Traceback (most recent call last):
  File "/data/data/com.termux/files/usr/lib/python3.8/multiprocessing/synchronize.py", line 28, in <module>
    from _multiprocessing import SemLock, sem_unlink
ImportError: cannot import name 'SemLock' from '_multiprocessing' (/data/data/com.termux/files/usr/lib/python3.8/lib-dynload/_multiprocessing.cpython-38.so)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/data/data/com.termux/files/usr/lib/python3.8/site-packages/pip/_internal/cli/base_command.py", line 188, in _main
    status = self.run(options, args)
  File "/data/data/com.termux/files/usr/lib/python3.8/site-packages/pip/_internal/commands/list.py", line 160, in run
    packages = self.get_outdated(packages, options)
  File "/data/data/com.termux/files/usr/lib/python3.8/site-packages/pip/_internal/commands/list.py", line 167, in get_outdated
    return [
  File "/data/data/com.termux/files/usr/lib/python3.8/site-packages/pip/_internal/commands/list.py", line 167, in <listcomp>
    return [
  File "/data/data/com.termux/files/usr/lib/python3.8/site-packages/pip/_internal/commands/list.py", line 216, in iter_packages_latest_infos
    pool = Pool(DEFAULT_POOLSIZE)
  File "/data/data/com.termux/files/usr/lib/python3.8/multiprocessing/dummy/__init__.py", line 124, in Pool
    return ThreadPool(processes, initializer, initargs)
  File "/data/data/com.termux/files/usr/lib/python3.8/multiprocessing/pool.py", line 922, in __init__
    Pool.__init__(self, processes, initializer, initargs)
  File "/data/data/com.termux/files/usr/lib/python3.8/multiprocessing/pool.py", line 196, in __init__
    self._change_notifier = self._ctx.SimpleQueue()
  File "/data/data/com.termux/files/usr/lib/python3.8/multiprocessing/context.py", line 113, in SimpleQueue
    return SimpleQueue(ctx=self.get_context())
  File "/data/data/com.termux/files/usr/lib/python3.8/multiprocessing/queues.py", line 336, in __init__
    self._rlock = ctx.Lock()
  File "/data/data/com.termux/files/usr/lib/python3.8/multiprocessing/context.py", line 67, in Lock
    from .synchronize import Lock
  File "/data/data/com.termux/files/usr/lib/python3.8/multiprocessing/synchronize.py", line 30, in <module>
    raise ImportError("This platform lacks a functioning sem_open" +
ImportError: This platform lacks a functioning sem_open implementation, therefore, the required synchronization primitives needed will not function, see issue 3770.

Steps to reproduce
run pip list --outdated

Expected behavior
Should output outdated python packages

[Grimler91]

Happens with pip 20.1, downgrading to 20.0.X works. Discussed previously in #5222 and linked issues

[landfillbaby]

in case you're curious, the next release of pip will have a fix for this, pypa/pip#8167 is the fix, already merged into master

[voidzero]

Until this gets pushed to the repos, how can I downgrade pip?

[landfillbaby]

pip install pip==20.0.2
or you could do what I've done and manually apply the patch from the PR mentioned above to your local pip 20.1 installation

[voidzero]

Ah, perfect. Thank you!

[landfillbaby]

also for future-proof checking of pip upgrades:
pip install -U pip!=20.1
currently also just installs 20.0.2 but will install the future fixed version as well, after which you can go back to normal

[landfillbaby]

pip 20.1.1 is out! this issue is fixed