Different Python projects usually employ not only different modules, but even different versions of the same module. The reason is that module developers push out new versions very rapidly and project maintainers may be slow on the uptake. Ideally, updates to any module (or package) should not break tools using previous implementations. Each update should add bug fixes and extend the API with new features, but not change it! However, programs are sometime built around some anomalous behavior of an API and bug fixes actually break said program.

As you work on different Python projects, you may need different versions of the same module. Probably even a module that you already have installed system-wide. For this, we use virtual environments. These environments allow you to install specific module versions in a local directory and alters your shell's environment to prioritize using them. Switching between environments can be as easy as sourceing another setup script.

The problem with virtual environments is that they don't mesh well with apt. In stead of apt, we will use a Python module manager called pip3. Our suggestion is to use pip only in virtual environments. Yes, it can also install modules system-wide, but most modules can be found as apt packages anyway. Generally, it is not a good idea to mix package managers!

First things first, we need python3, the venv module, and pip. These, we can get with apt

$ sudo apt install python3 python3-venv python3-pip

Assuming that you are in your project's root directory already, we can set up the virtual environment:

$ python3 -m venv .venv

The -m flag specifies to the Python interpreter a module. python3 searches its known install paths for said module (in this case, venv) and runs it as a script. .venv is the script's argument and represents the name of the storage directory. Take a look at its internal structure:

$ tree -L 3 .venv

Notice that in .venv/bin/ we have both binaries and activation scripts. These scripts, when sourced, will force the current shell to prioritize using these. The modules you install will be placed in .venv/lib/python3.*/site-packages/. Try to activate your environment now. Once active, you will have access to the deactivate command that will restore your previous environment state:

$ source .venv/bin/activate
$ deactivate

VIRTUAL_ENV_DISABLE_PROMPT="yes"

Same as apt, pip used to have a search function for modules. Unfortunately, they removed this feature due to a high number of queries. Now, to search for modules, you will need to use the web interface.

Let us install the modules needed for this laboratory. After that, let us also check the versions of all modules (some will be added implicitly). Can you also find their installation path in the .venv/ directory?

$ sudo apt install libffi-dev libnacl-dev python3-dev
 
$ pip3 install 'py-cord[voice]' PyNaCl ipython
$ pip3 list

So, what are these, exactly?

• py-cord[voice]: a Python module that interacts with discord. The previous discord.py project has been discontinued and pycord remains the best alternative. We'll be using this in the following exercise to write a discord bot.
• PyNaCl: wrapper of the NaCl library. This library offers a high-level interface for networking and cryptographic operations. Note that the library must be installed using apt and that which we install with pip is only a wrapper.
• ipython: a more interactive Python. See the next task for some details, but there's really not much to it.

$ pip3 freeze > requirements.txt
$ pip3 install -r requirements.txt

In the previous lab, you used the python3 interpreter in interactive mode. Now, we upgrade to ipython. This new interpreter offers an enhanced user experience by means of color coding, tab completion, multi-line editing, etc. For scripting purposes, python3 should remain your interpreter of choice. But for prototyping, we suggest using this. For now, let's see if the discord module in the py-cord[voice] package is available to import.

$ ipython
Python 3.9.7 (default, Oct 10 2021, 15:13:22) 
Type 'copyright', 'credits' or 'license' for more information
IPython 7.29.0 -- An enhanced Interactive Python. Type '?' for help.
 
In [1]: import discord
 
In [2]: discord?
 
In [3]: discord??
 
In [4]: help(discord)

Note how in stead of help, in ipython we can ? or ?? to something to access a brief / more complete documentation.