Editing Virtual Environments with Python

[[Category:Python]] [[Category:Web Development]]
== Overview ==

Mac OS X Yosemite comes with Python 2.7 installed. 

After [[Installing Python 3 on Mac OS|installing Python 3.4]], the `python` command still invokes Python 2.x. To use Python 3 use the `python3` command instead.

Similarly, the `pip` command invokes pip that was installed with Python 2.x. So, `pip install [package_name]` will install for Python 2.x and leave Python 3.x unchanged. `pip3` can be used to update Python 3.x on the command line. ''(`pip3` is installed as part of the Python 3.x package.)''

== Creating virtual environments on Mac ==

=== Using python3 ===

Per the Python 3.8.x documentation, a virtual environment can be created with: <ref>[https://docs.python.org/3/library/venv.html venv - Creation of Virtual Environments] - Python Standard Library Documentation</ref>

<pre>
$ python3 -m venv /path/to/new/environment/
</pre>

`venv` is the command that is run with python to create the virtual environment.

=== Using virtualenv ===

First, install `virtualenv` if it is not already installed: `pip(3) install virtualenv`. A new terminal shell is required to have the `virtualenv` command available.<ref>[http://stackoverflow.com/a/10763461 Build a `virtualenv` of python 3] - Stack Overflow</ref>

<syntaxhighlight lang="sh">
$ virtualenv -p /Library/Frameworks/Python.framework/Versions/3.4/bin/python3 venv
$ source venv/bin/activate
$ pip install package-name
</syntaxhighlight>

== Activating a virtual environment ==

An existing virtual environment is activated with:

<syntaxhighlight lang="sh">
$ source ~/venv/bin/activate
</syntaxhighlight>

On Windows: `.\venv\scripts\activate`

To exit the virtualenv enter `deactivate` at the command prompt. This routine is defined within the virtualenv `activate` script.

To find the path to Python 3.x: 

<syntaxhighlight lang="sh">
$ which python3
</syntaxhighlight>

''N.B. Packages will probably have to be installed for new virtual environments, e.g. django, etc.''

== Using a virtual environment in PyCharm ==

* '''PyCharm''' > '''Preferences''' > '''Project: '[CURRENT_PROJECT]'''' > '''Project Interpreter'''
** Click the gear icon to the right of '''Project Interpreter:'''
*** Choose '''Add Local''' for existing virtualenv, or '''Create VirtualEnv''' for a new one
*** Select the virtualenv, and apply the changes.<ref>[https://www.jetbrains.com/pycharm/help/creating-virtual-environment.html Creating Virtual Environment] - PyCharm 4.5.3 Help</ref>

== Deactivating a virtual environment ==

<syntaxhighlight lang="sh">
$ deactivate
</syntaxhighlight>

== Updating the python version for an existing virtual environment ==

First, deactivate the virtual environment if it is running. <ref>[https://stackoverflow.com/a/51915509 How to change the python version of already existing virtualenv?] - Stackoverflow</ref>

<syntaxhighlight lang="sh">
$ virtualenv --clear -p /path/to/my/python3.6 ./venv
</syntaxhighlight>

Confirm the python version used by the virtual environment with: 

<syntaxhighlight lang="sh">
$ ls -la ./venv/bin/python
</syntaxhighlight>

== Notes ==

=== See also ===

* [https://docs.python-guide.org/dev/virtualenvs/ Pipenv & Virtual Environments] - The Hitchhiker's Guide to Python
* [http://hackercodex.com/guide/python-development-environment-on-mac-osx/#virtualenv Python Development Environment on Mac OS X Yosemite 10.10: virtualenv] - Hacker Codex

=== References ===

<references />