Removing pip's cache?

If using pip 6.0 or newer, try adding the --no-cache-dir option (source).

If using pip older than pip 6.0, upgrade it with pip install -U pip.

Clear the cache directory where appropriate for your system

Linux and Unix

~/.cache/pip  # and it respects the XDG_CACHE_HOME directory.

OS X

~/Library/Caches/pip

Windows

%LocalAppData%\pip\Cache

UPDATE

With pip 20.1 or later, you can find the full path for your operating system easily by typing this in the command line:

pip cache dir

Example output on my Ubuntu installation:

➜ pip3 cache dir/home/tawanda/.cache/pip

(pip maintainer here!)

The specific issue of "installing the wrong version due to caching" issue mentioned in the question was fixed in pip 1.4 (back in 2013!):

Fix a number of issues related to cleaning up and not reusing build directories. (#413, #709, #634, #602, #939, #865, #948)

Since pip 6.0 (back in 2014!), pip install, pip download and pip wheel commands can be told to avoid using the cache with the --no-cache-dir option. (eg: pip install --no-cache-dir <package>)

Since pip 10.0 (back in 2018!), a pip config command was added, which can be used to configure pip to always ignore the cache -- pip config set global.cache-dir false configures pip to not use the cache "globally" (i.e. in all commands).

Since pip 20.1, pip has a pip cache command to manage the contents of pip's cache.

• pip cache purge removes all the wheel files in the cache.
• pip cache remove matplotlib selectively removes files related to a matplotlib from the cache.

In summary, pip provides a lot of ways to tweak how it uses the cache:

• pip install --no-cache-dir <package>: install a package without using the cache, for just this run.
• pip config set global.cache-dir false: configure pip to not use the cache "globally" (in all commands)
• pip cache remove matplotlib: removes all wheel files related to matplotlib from pip's cache.
• pip cache purge: to clear all files from pip's cache.