freeze Python

In this article we will discuss working with colleagues in a virtual environment.

You can study the installation of virtualenv in the article «Installing virtualenv» and working in it in the article «Using virtualenv«

If in a command you see a \ in the path, it means it is for Windows

If it is /, then for Linux or MacOS

Often it is enough just to change the type of slash and the command will work on your OS

Suppose we are in the directory virtualenvs and have activated our virtual environment myvenv

To check which package versions freeze sees, run

python -m pip freeze

or, if the command above showed nothing

python -m pip freeze --all

To write everything to a file, run

python -m pip freeze > requirements.txt
cat .\requirements.txt

certifi==2020.4.5.2
chardet==3.0.4
idna==2.9
requests==2.23.0
urllib3==1.25.9

In the file requirements.txt there is now a description of our virtual environment myvenv, namely the list of all installed packages and their versions.

If you are familiar with nmp this file may remind you of package.json

Now you can leave this environment, create a new one and activate it

deactivate

Let us create a new environment new_venv, activate it and see which packages are installed.

python -m venv new_venv

Then, if you are on Windows execute

nev_venv\Scripts\Activate.ps1

And if on Linux or MacOS, run

source ./nev_venv/bin/activate

After activation, run

python -m pip list

There are only two packages and even the pip version is lower than in the previous environment.

To install all the packages mentioned in the requirements.txt file, run

python -m pip install -r .\requirements.txt

And check what was installed

python -m pip list

All packages are in place and in the required versions. This is true for not too complex projects. We will talk about possible problems at the end of the article.

Note that the pip version did not change.

python -m pip install requests

Let us check which packages were installed

python -m pip list

request pulled in four more packages: certifi, chardet, idna, urllib3

You can check where requests was installed in this environment with the command

python -m pip show requests

To exit the virtual environment we use the command

deactivate

If you now run

python -m pip show requests

WARNING: Package(s) not found: requests

You can see that globally requests is not installed at all

Starting with Python 3.6 it is recommended to create virtual environments with the command

python -m venv myvenv

The environment is activated in the same way

myvenv\Scripts\Activate.ps1

(myvenv) PS C:\Users\Andrei\virtualenvs>

I do not know about yours, but on mine in PowerShell (myvenv), created with venv is highlighted in green, while test_env, created with virtualenv stays grey.

requirements.txt

Into the file requirements.txt the list of dependencies is exported.

By dependencies we mean the packages that are necessary for the project to work

Dependencies may have their own dependencies and there may be conflicts between them.

For example, your project depends on the packages X and Y. X depends on Z version 1.0 and Y on Z version 2.0 and does not work with Z 1.0. But X in turn does not work with Z 2.0

What will happen in this case? I will not venture to say, but pip will install some version.

Article author: Andrei Olegovich