Meta: this "how do I manage multiple Pythons?" thing has come up a couple of times lately; are people interested in a FAQ section?
On 23 October 2016 at 03:54, Eugene Yunak <[email protected]> wrote: > I'd set the shebang to `/usr/bin/env python3`, or `/usr/bin/env python` if you > do not care whether 2 or 3 would be used. Use `virtualenv' (you may need to install it separately; `pip install virtualenv') if you need to use a mix of Python versions, and always use the latter shebang form. So, an example. Say you found two Python apps that you want to use. Let's call them "oldapp" and "newapp". oldapp needs python 2.7 and newapp is OK with python 3+. Both include 'requirements.txt' files to indicate what their Python package dependencies are. If it's a popular app you may be able to install the app this way as well, with the `pip' utility, thus keeping it all nicely contained within the virtualenv. But I'll assume that that's not possible here. The apps are installed in $HOME/apps/oldapp and $HOME/apps/newapp 1. After installing both Pythons, make a place to keep your virtualenvs mkdir $HOME/py 2. Create the virtualenvs and install dependencies virtualenv -p /usr/local/bin/python2.7 $HOME/py/oldapp . $HOME/py/newapp/bin/activate python --version ### to demonstrate that virtualenv works pip install -r $HOME/apps/oldapp/requirements.txt virtualenv -p /usr/local/bin/python3 $HOME/py/newapp . $HOME/py/newapp/bin/activate python --version ### to demonstrate that virtualenv works pip install -r $HOME/apps/newapp/etc/requirements.txt 3. Observe that all of these dependencies are installed inside the relevant virtualenv. So they will never conflict with each other or pollute your /usr/local tree. 4. To actually run an app . $HOME/py/newapp/bin/activate $HOME/apps/newapp/bin/newapp.py . $HOME/py/oldapp/bin/activate $HOME/apps/oldapp/bin/oldapp.py Hope this helps. John
