Updating 'pip' after configuring 'pip' to point to Homebrew's pip3 causes errors

问题

After installing Python 3 using Homebrew and putting the Homebrew aliases (e.g. pip -> pip3) on my path

export PATH=/usr/local/opt/python/libexec/bin:$PATH

and then updating pip with

pip3 install -U pip

I get errors whenever I run pip:

pkg_resources.VersionConflict: (pip 19.1 (/usr/local/lib/python3.7/site-packages), Requirement.parse('pip==19.0.3'))

How do I configure my Homebrew Python 3 correctly with pip3 so that updates to pip (and other packages) work when the aliases provided with Homebrew's Python 3 are on my path?

来源：https://stackoverflow.com/questions/55871398/updating-pip-after-configuring-pip-to-point-to-homebrews-pip3-causes-errors