Switch between python 2.7 and python 3.5 on Mac OS X

Question

I generally use Python 2.7 but recently installed Python 3.5 using Miniconda on Mac OS X. Different libraries have been installed for these two versions of python. Now, the entering either of the keywords 'python' or 'python3' in terminal invokes python 3.5, and 'python2' returns '-bash: python2: command not found'. How can I now invoke them specifically using aliases 'python2' and 'python3' respectively?

I am currently using OS X El Capitan.

Solution 1

IMHO, the best way to use two different Python versions on macOS is via homebrew. After installing homebrew on macOS, run the commands below on your terminal.

brew install python@2
brew install python

Now you can run Python 2.7 by invoking python2 or Python 3 by invoking python3. In addition to this, you can use virtualenv or pyenv to manage different versions of python environments.

I have never personally used miniconda but from the documentation, it looks like it is similar to using pip and virtualenv in combination.

Solution 2

OSX's Python binary (version 2) is located at /usr/bin/python

if you use which python it will tell you where the python command is being resolved to. Typically, what happens is third parties redefine things in /usr/local/bin (which takes precedence, by default over /usr/bin). To fix, you can either run /usr/bin/python directly to use 2.x or find the errant redefinition (probably in /usr/local/bin or somewhere else in your PATH)

Solution 3

I already had python3 installed(via miniconda3) and needed to install python2 alongside in that case brew install python won't install python2, so you would need brew install python@2 .

Now alias python2 refers to python2.x from /usr/bin/python

and alias python3 refers to python3.x from /Users/ishandutta2007/miniconda3/bin/python

and alias python refers to python3 by default.

Now to use python as alias for python2, I added the following to .bashrc file

alias python='/usr/bin/python'.

To go back to python3 as default just remove this line when required.

Solution 4

Similar to John Wilkey's answer I would run python2 by finding which python, something like using /usr/bin/python and then creating an alias in .bash_profile:

alias python2="/usr/bin/python"

I can now run python3 by calling python and python2 by calling python2.

Solution 5

Here is how to set the Python version back to 2.7 if you have installed Anaconda3 (Python 3.6) on MacOS High Sierra 10.13.5.

1. Edit the .bash_profile file in your home directory.
2. vi $HOME/.bash_profile
3. Comment out the line with anaconda3 addition to your PATH like this:

   # export PATH="/Users/YOURUSERNAME/anaconda3/bin:$PATH"
   

4. Close the shell, then open it again
5. You should now see 2.7 when you run python

Then, if you want 3.6 you can simply uncomment out the anaconda3 line in your .bash_profile.

Trying to unlink python will end in tears in Mac OS X.

You will get something like this

unlink: /usr/bin/python: Operation not permitted

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Comments

[TigerhawkT3]

Have you tried python -2?

[Emil Vikström]

Sounds like you should open a bug report with Miniconda that they are not following PEP-0394.

[David Z]

What do you mean by switching between them? Do you want to be able to invoke Python 2 specifically, when you want it, and invoke Python 3 specifically when you want that version? That you can do using the aliases python2 and python3 (and I'll post that as an answer if this is what you want and you edit your question accordingly). Or do you want to switch which version of Python actually runs when you type just python?

[Charlie Parker]

even if your able to run python2 you might need to re-install things for python 2 it seems...

[Viswanath]

But, I'm looking for the way to create an alias, say python2 to invoke Python 2 and python3 to invoke Python 3. Could you give me some information on that direction? Thnx.

[Charlie Parker]

how does one install things for python2 now?

[forevergenin]

pip2 install <package_name>