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Python Virtual Environment Reference Manual

This short document presents virtualenv setup guide for iCeDeROM project.

In short words Virtualenv is a dedicated and independent container for Python Application along with its Dependencies. Different Operating Systems may be bundled with different versions of Python and different set of available packages by default. This makes project deployment and maintenance difficult, if possible at all. This is why we want to create from scratch dedicated environment that we can control. Virtualenv is here to make it happen in an automated way.

Using Virtualenv

iCeDeROM project contains several scripts that will make it easier for you develop, test, and deploy it using provided Virtualenv. Assuming that you already did a successful setup of Virtualenv:

  • venv.sh script will take you inside bash shell with target python environment in path, so you can test some code.
  • iCeDeROM.sh script will launch the application using virtualenv.

Creating Virtualenv

  • We are using the Python 3.6 interpreter and so python3.6 -m venv.
  • You can get Python [directly from the Python Project Website] (https://www.python.org/downloads/) or using your Operating System Package Management.
  • iCeDeROM assumes virtualenv location at ../venv/default/ from the project root (that is where venv.sh is located). This location is important!
  • If you work with PyCharm IDE go to Preferences / Project / Interpreter and use creator to make all work for you.
  • You can create Virtualenv from a Terminal (copies will copy the files instead of creating symlinks, clear will clear the target directory if existed previously):
$ mkdir ../venv
$ python3.6 -m venv --copies --clear ../venv/macos-python-3.6
$ ln -s macos-python-3.6 ../venv/default
  • You can have multiple instances of virtualenv in ../venv directory, for instance when you develop on MacOS and deploy on FreeBSD, just remember to link the one you need as default.
  • Virtualenv shell requires bash to run.
  • You can test your setup with:
$ pwd
/(...)/iCeDeROM/iCeDeROM.git
$ ./venv.sh
(macos-python-3.6) pwd
/(...)/iCeDeROM/iCeDeROM.git
(macos-python-3.6) which python
/(...)/iCeDeROM/venv/macos-python-3.6/bin/python
(macos-python-3.6) python
Python 3.6.0 (default, Dec 23 2016, 12:50:55)
[GCC 4.2.1 Compatible Apple LLVM 8.0.0 (clang-800.0.38)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>

Installing dependencies

After you have installed the virtualenv you need to install project dependencies, that is libraries and modules that the project depends on. Here is an example:

$ ./venv.sh
(macos-python-3.6) pip install -r requirements.txt
...
(C) 2017 [CeDeROM Tomasz CEDRO](http://www.tomek.cedro.info), All rights reserved! :-)