Managing Python Environments and Dependencies


The great thing about Python is that whatever problems (including IoT problems) we are trying to solve, there is a very high chance there’s is a Python library out there that’s going to make our life a lot easier. The troublesome thing about Python is that, even at this point in time, there is still two Python universe and it makes life very hard for those that wants to move forward.

Let’s consider the following scenario:

  • We have a solution that depends on a set of libraries and at specific versions.
  • Those libraries also depends on other libraries and also at specific versions.
  • Runs on Python 2.7
  • Libraries owners may not have the time to migrate to Python 3.

If we take the above scenario and try to migrate the solution to Python 3, we might be looking at a very long dark tunnel.

The Windows method (Windows 10)

Anyway, the purpose of this blog is not solving our migration problems but more about keeping things nice and tidy, manageable, and us developers happy. To do that we will discuss some concepts that every Python developers should be familiar with:

  • Python Launcher
  • Virtual Environments
  • Pip
Python Launcher

Python Launcher is a Windows utility used to identify which Python versions as well as where they are installed. It also provide a mechanism to launch Python programs with a specified Python interpreter.

For my development environment, I know that I need to work with both Python 2 and Python 3 so we ‘ll head over to python.org download page now and download the latest version for each (in my case they were Python 3.9.5 and Python 2.7.18). Also since Python Launcher was introduced in Python 3.3, installing Python 3.9.5 will also install Python Launcher.

Now that we downloaded the installation files, let’s install them.

Installing Python 2.7.18
Installing Python 3.9.5

After installation has been completed, open a terminal window and execute the command “py –help” which will print out the help for “py” (Python Launcher).

Python launcher command demo
Virtual Environments

Python virtual environment allows developers to create self-contained environments when working in Python. My preferred workflow is to create a virtual environment per project I work with so that Python version and external libraries are only relevant to the environment they were created in. Below are examples of create a Python 2 and Python 3 virtual environment, as well as activating and deactivating them.

PS D:\Workspace> mkdir python2-project-demo
    Directory: D:\Workspace
Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           5/06/2021 08:45 pm                python2-project-demo
PS D:\Workspace> cd .\python2-project-demo\
PS D:\Workspace\python2-project-demo> py -2 -m virtualenv venv
created virtual environment CPython2.7.18.final.0-64 in 8526ms
  creator CPython2Windows(dest=D:\Workspace\python2-project-demo\venv, clear=False, no_vcs_ignore=False, global=False)
  seeder FromAppData(download=False, pip=bundle, wheel=bundle, setuptools=bundle, via=copy, app_data_dir=C:\Users\Chris\AppData\Local\pypa\virtualenv)
    added seed packages: pip==20.3.4, setuptools==44.1.1, wheel==0.36.2
  activators PythonActivator,FishActivator,BatchActivator,BashActivator,PowerShellActivator
PS D:\Workspace\python2-project-demo> ls
    Directory: D:\Workspace\python2-project-demo
Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           5/06/2021 08:46 pm                venv
PS D:\Workspace\python2-project-demo> .\venv\Scripts\activate
(venv) PS D:\Workspace\python2-project-demo> python -V
Python 2.7.18
(venv) PS D:\Workspace\python2-project-demo> deactivate
PS D:\Workspace\python2-project-demo>
PS D:\Workspace> mkdir python3-project-demo
    Directory: D:\Workspace
Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           6/06/2021 08:50 pm                python3-project-demo
PS D:\Workspace> cd .\python3-project-demo\
PS D:\Workspace\python3-project-demo> py -3 -m venv venv
PS D:\Workspace\python3-project-demo> ls
    Directory: D:\Workspace\python3-project-demo
Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           6/06/2021 08:51 pm                venv
PS D:\Workspace\python3-project-demo> .\venv\Scripts\activate
(venv) PS D:\Workspace\python3-project-demo> python -V
Python 3.9.5
(venv) PS D:\Workspace\python3-project-demo> deactivate
PS D:\Workspace\python3-project-demo>
Pip

Pip is a Python package installer. It is used for installing and managing external libraries for a given Python environment.

One reason I use Python is when working with CoAP. CoAP is a client/server transport protocol ideally used for communicating with constraint resource devices. In Python 2.7, CoAPthon is a good library to use. While in Python 3, Aiocoap is a nice option.

Using the Python 3 virtual environment created earlier, we will take a look at some of the useful pip commands.

Installing external packages, we can use “pip install <package-to-install>”.

(venv) PS D:\Workspace\python3-program> pip install aiocoap
Collecting aiocoap
  Using cached aiocoap-0.4.1.tar.gz (201 kB)
Building wheels for collected packages: aiocoap
  Building wheel for aiocoap (setup.py) ... done
  Created wheel for aiocoap: filename=aiocoap-0.4.1-py3-none-any.whl size=181210 sha256=09fafe85ee179a31e52bb57b088af1fcdf3e4114b664c6af7615af5715feb54c
  Stored in directory: c:\users\chris\appdata\local\pip\cache\wheels\2c\a6\f8\63466bc1a04e8fb6e88707a6005a65529e451f02221e88f542
Successfully built aiocoap
Installing collected packages: aiocoap
Successfully installed aiocoap-0.4.1
(venv) PS D:\Workspace\python3-program> 

We can use “pip list” to list all installed packages.

(venv) PS D:\Workspace\python3-program> pip list
Package    Version
---------- -------
aiocoap    0.4.1
pip        21.1.2
setuptools 56.0.0
wheel      0.36.2
(venv) PS D:\Workspace\python3-program>

We can use “pip show <package-to-show>” to show package details.

(venv) PS D:\Workspace\python3-program> pip show aiocoap
Name: aiocoap
Version: 0.4.1
Summary: Python CoAP library
Home-page: https://github.com/chrysn/aiocoap
Author: Maciej Wasilak, Christian Amsüss
Author-email: c.amsuess@energyharvesting.at
License: MIT
Location: d:\workspace\python3-program\venv\lib\site-packages
Requires:
Required-by:
(venv) PS D:\Workspace\python3-program>

We can use “pip list –format=freeze > requirements.txt” to export the list to a file which could then be used in another virtual environment.

(venv) PS D:\Workspace\python3-program> pip list --format=freeze > requirements.txt
(venv) PS D:\Workspace\python3-program> Get-Content .\requirements.txt
aiocoap==0.4.1
pip==21.1.2
setuptools==56.0.0
wheel==0.36.2
(venv) PS D:\Workspace\python3-program> deactivate
PS D:\Workspace\python3-program> cd ..
PS D:\Workspace> mkdir python3-program-v2

    Directory: D:\Workspace

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----           7/06/2021 8:46 pm                python3-program-v2

PS D:\Workspace> cd .\python3-program-v2\
PS D:\Workspace\python3-program-v2> py -3 -m venv venv
PS D:\Workspace\python3-program-v2> .\venv\Scripts\activate
(venv) PS D:\Workspace\python3-program-v2> pip list
Package    Version
---------- -------
pip        21.1.1
setuptools 56.0.0
WARNING: You are using pip version 21.1.1; however, version 21.1.2 is available.
You should consider upgrading via the 'd:\workspace\python3-program-v2\venv\scripts\python.exe -m pip install --upgrade pip' command.
(venv) PS D:\Workspace\python3-program-v2> python.exe -m pip install --upgrade pip
Requirement already satisfied: pip in d:\workspace\python3-program-v2\venv\lib\site-packages (21.1.1)
Collecting pip
  Using cached pip-21.1.2-py3-none-any.whl (1.5 MB)
Installing collected packages: pip
  Attempting uninstall: pip
    Found existing installation: pip 21.1.1
    Uninstalling pip-21.1.1:
      Successfully uninstalled pip-21.1.1
Successfully installed pip-21.1.2
(venv) PS D:\Workspace\python3-program-v2> cp ..\python3-program\requirements.txt .
(venv) PS D:\Workspace\python3-program-v2> pip install -r .\requirements.txt
Collecting aiocoap==0.4.1
  Using cached aiocoap-0.4.1-py3-none-any.whl
Requirement already satisfied: pip==21.1.2 in d:\workspace\python3-program-v2\venv\lib\site-packages (from -r .\requirements.txt (line 2)) (21.1.2)
Requirement already satisfied: setuptools==56.0.0 in d:\workspace\python3-program-v2\venv\lib\site-packages (from -r .\requirements.txt (line 3)) (56.0.0)
Collecting wheel==0.36.2
  Using cached wheel-0.36.2-py2.py3-none-any.whl (35 kB)
Installing collected packages: wheel, aiocoap
Successfully installed aiocoap-0.4.1 wheel-0.36.2
(venv) PS D:\Workspace\python3-program-v2> pip list
Package    Version
---------- -------
aiocoap    0.4.1
pip        21.1.2
setuptools 56.0.0
wheel      0.36.2
(venv) PS D:\Workspace\python3-program-v2>

The Linux method (Raspberry Pi OS)

Installing the latest Python Interpreter

At the time of writing, Python 3.9 was the latest version, however this was not installed by default.

Check installed Python demo

We can install Python 3.9 from source. Python 3.9 install on Raspberry PI OS is a good post showing how we can go about doing that.

Install from source demo

Categories: Python, Tooling

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