Sam Hooke

These are rough notes from whatever I was working on, interested in or thinking about at the time. They vary greatly in quality and length, but prove useful to me, and hopefully to you too!

Python DEPRECATION warning and pip --no-cache-dir breakage

Today, Python 2.7’s pip started echoing the following:

DEPRECATION: Python 2.7 will reach the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 won't be maintained after that date. A future version of pip will drop support for Python 2.7.

Simultaneously (and perhaps related, though perhaps coincidentally) Python 2.7’s pip started giving the following error:

  File in "...\lib\site-packages\pip\_internal\cli\base_command.py", line 176, in main
    status = self.run(options, args)
  File in "...\lib\site-packages\pip\_internal\commands\install.py", line 346, in run
    session=session, autobuilding=True
  File in "...\lib\site-packages\pip\_internal\wheel.py", line 848, in build
    assert building_is_possible
AssertionError

Looking at the wheel.py source, there is a TODO above the the assert building_is_possible line:

        # TODO: This check fails if --no-cache-dir is set. And yet we
        #       might be able to build into the ephemeral cache, surely?
        building_is_possible = self._wheel_dir or (
            autobuilding and self.wheel_cache.cache_dir
        )
        assert building_is_possible

Sure enough, we are using the --no-cache-dir option when we call pip.

Removing the call to --no-cache-dir fixes the AssertionError, however we still need pip to not use cached packages.

As a workaround, we can empty the entire pip cache.

The pip cache has a different location depending upon the OS.

  • Windows: %LOCALAPPDATA%\pip\Cache
  • Linux: ~/.cache/pip
Windows
DEL /f /s /q %LOCALAPPDATA%\pip\Cache
RMDIR /s /q %LOCALAPPDATA%\pip\Cache

(We call DEL and RMDIR because otherwise we get “The directory is not empty”.

Linux
rm -rf ~/.cache/pip

It is unclear whether the DEPRECATION message and the AssertionError from --no-cache-dir are related, but in this case neither pip nor Python 2.7 were upgraded – these both seemingly started on their own accord.

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