venv中的pip install requirements.txt：如何忽略不同版本的系统站点包？

Question

I am in a virtual environment which shares the system site packages (created with venv in Python 3.5), and I would like to install all packages in a given requirements.txt into this venv. The system-wide python installation is read-only, so I cannot modify it.

Now, for example, my requirements.txt lists, among many others,

SomePackage==2.0

as requirement, while the system installation already contains SomePackage-1.0 . Pip thus tries to uninstall SomePackage-1.0 to upgrade to version 2.0. This, however, fails because the system-wide python installation is read-only.

Is there a way to run pip install -r requirements.txt in a way that ignores installed packages if they have a different version from the required one and just installs the required version into the venv?

I guess this would be similar to installing each package one by one and using --ignore-installed whenever the package is already present in a different version than the required one. This, however, seems quite cumbersome. Is there a better way?

Note that I am using a venv with shared system site packages because I want to avoid the installation of several huge packages each time I create a new venv. Thus I do not want to switch to a fully isolated venv, which would, of course, not have the above issue.

Any hint would be greatly appreciated! Thanks a lot!

Answer 1

To list only the packages you need for your project inside venv, and not all global packages from your computer, first you have to activate the virtualenv, and from (env) to run pip freeze > requirements.txt command.

So you will have strictly listed the packages you need for the specified project.