How can I specify optional dependencies in a pip requirements file? According to the pip documentation this is possible, but the documentation doesn't explain how to do it and I can't find any examples on the web.
Instead of specifying optional dependencies in the same file as the hard requirements, you can create a optional-requirements.txt and a requirements.txt.
To export your current environment's packages into a text file, you can do this:
pip freeze > requirements.txt
If necessary, modify the contents of the requirements.txt to accurately represent your project's dependencies. Then, to install all the packages in this file, run:
pip install -U -r requirements.txt
-U tells pip to upgrade packages to the latest version, and -r tells it to install all packages in requirements.txt.
In 2015 PEP-0508 defined a way to specify optional dependencies in requirements.txt:
requests[security]
That means that yourpackage needs requests for its security option. You can install it as:
pip install yourpackage[security]
You are misunderstanding the docs; they are not as clear as they could be. The point in the docs is that with a requirements file you can feel free to specify your full recommended working set of packages, including both necessary dependencies and optional ones. You can add comments (lines beginning with #) to distinguish the two to humans, but pip makes no distinction. You can also have two requirements files, as Daniel suggests.
来源：https://stackoverflow.com/questions/3664478/optional-dependencies-in-a-pip-requirements-file