I have a related issue. My underlying ‘problem’ seems to share its causality with what has been discussed with regards to @aabdnn 's problem.
I use MacOs Terminal.
$ which python
/usr/bin/python (macos preinstalled)
$ which python3
$ pip --version
-bash: pip: command not found
$ which pip3
/usr/local/bin/pip3 (from brew python3 formula install)
then I run (as recommended per official brew Python docs)
python3 -m pip install --upgrade pip
note: I used python3 not python as per literal documentation
$ which pip
$ which pip3
both pips are the same version
then I remove the /usr/local/bin/pip file, as it was not there before my pip upgrade and it annoys me.
things go back to as before
Question1: blabla - own answer: I will not upgrade pip manually again, but rather wait for brew python formula update.
Question2: I deleted that /usr/local/bin/pip file that seems to have been created (against my will or expectation) after running the pip upgrade.
My pip and pip3 command seem to work, or not work in the case of pip, as was prior to the upgrade. But was this file removal good clean practice or am I set for trouble later on? Edit: I recall that the file was an executable called pip and it was the newest version.