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

Okay, this is what I gathered:

• Don't delete the Python framework!
• If it's deleted, then python3 --version won't work
• Just install Python from the Python website
• The framework will return and python3 --version will work

Answer 2

I had the same issue. I learned how to fix it for good:

1. Open "Applications" in Mac Finder and drag Python to the trash bin.
2. Empty the trash bin

If you have an error as above, then an official Python installation has been performed (as others have mentioned) via e.g. Python.org. This creates some kind of alias for the python or python3 commands outside a Bash alias. So while the command where python3 may point to /usr/local/bin/python3, python3 will still try to call /Library/Frameworks/Python.framework/Versions/3.5/bin/python3.

Note:

• the MacOS system Python is /usr/bin/python
• Homebrew Python(s) will be located in /usr/local/bin/
• Pythons installed as an Apple application live in /Library/Frameworks/Python.framework/

Answer 3

I think I detected which is the problem.

I guess that, in a certain moment, you had installed python from the official site instead of via Homebrew. In my case, I installed via the official website Python 3.6.4. A few months later, I wanted to upgrade it, and noticed that it was very complex. So, I decided to move to Homebrew. Open a terminal window and let's try to fix this: 1. First, let's uninstall previous Python versions:

    sudo rm -rf /Library/Frameworks/Python.framework
    sudo rm -rf /usr/local/bin/python3

2. Then, remove the previous frameworks from the $PATHvariable:

    nano ~/.bash_profile

You will see something like that:

    # Setting PATH for Python 2.7
    # The original version is saved in .bash_profile.pysave
    PATH="/Library/Frameworks/Python.framework/Versions/2.7/bin:${PATH}"
    export PATH

    # Setting PATH for Python 3.6
    # The original version is saved in .bash_profile.pysave
    PATH="/Library/Frameworks/Python.framework/Versions/3.6/bin:${PATH}"
    export PATH`

This is the problem: These paths don't exist. Comment the $PATH editions (or erase them):

    # Setting PATH for Python 2.7
    # The original version is saved in .bash_profile.pysave
    # PATH="/Library/Frameworks/Python.framework/Versions/2.7/bin:${PATH}"
    # export PATH

    # Setting PATH for Python 3.6
    # The original version is saved in .bash_profile.pysave
    # PATH="/Library/Frameworks/Python.framework/Versions/3.6/bin:${PATH}"
    # export PATH

3. Restart the computer and install via Homebrew Python 2 and 3:

    brew update
    brew install python
    brew install python3

This worked for me. Now, if type python3 --version I get Python 3.7.0, and everything works fine :)

Answer 4

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.