Unable to Run Python 3 After Homebrew Installation

Question

After installing Homebrew using the script on their homepage and checking if everything was alright with brew doctor, I issued brew install python3

Answer 1

This error:

-bash: /Library/Frameworks/Python.framework/Versions/3.5/bin/python3: No such file or directory

suggests a remnant of some previous (attempt at an) installation of Python 3 using a different way (not Homebrew).

(I think this is actually where the Python installation from www.python.org goes. I wouldn't know though, as I've either never tried that package, but only installed the www.python.org version from source. This would suggest, though, that you already had an attempt at installing Python 3.5, something failed, and you're now trying Homebrew instead.)

I'd suggest moving (renaming) this out of the way, so your system doesn't pick it up. Something like

mv /Library/Frameworks/Python.framework/Versions/3.5 /Library/Frameworks/Python.framework/Versions/3.5-aside

(if there other versions of Python 3 in that directory, you may want to do the same for those.)

Also check that python3 isn't an alias. Commands such as

which python3
type python3
alias python3

will reveal that.

With the interfering Python 3 out of the way, try re-installing Python 3 through homebrew again. You may have to do an uninstall + reinstall.
Read carefully any homebrew messages once the installation is done, in particular if it mentions something about linking files: you may need to run something like brew link python3.