Why does pip install requirements.txt install extra packages?

问题

I have a repository with an inflated requirements.tx that I'd like to clean up. Using pipreqs I've set my requirements.txt to be a minimal set of packages need for my repository. To test this, I setup a virtualenv to install the packages and then run all my unit tests to make sure they're satisfactory.

virtualenv temp_venv --no-site-packages
source temp_venv/bin/activate
pip install -r requirements.txt

Which runs fine, but I see that a whole bunch of extra packages are collected and installed. Why? Are these identified as needed by required packages, and thus installed? If so, should I then include them in the requirements.txt?

回答1:

Yes. The packages are dependencies of your dependencies​.

But no, you should not specify them directly. Automatic tools know to download dependencies recursively and it would significantly add to maintenance overhead.

回答2:

This might have been because of the dependencies of your written libs in requirements.txt. For ex: if you have written scipy as requirement numpy will also be installed because scipy is dependent on numpy.

来源：https://stackoverflow.com/questions/42919181/why-does-pip-install-requirements-txt-install-extra-packages