Existing Projects

Let's clone fastapi, which uses a pyproject.toml without setup.py or requirements.txt:

% git clone https://github.com/tiangolo/fastapi
% cd fastapi
% envin

Since no (*-)requirements.txt files were found, envin has not installed the project's dependencies.

You may compile a requirements.txt directly from pyproject.toml:

[venv] % pipcs pyproject.toml -- -o requirements.txt --extra dev,test

But the resulting lockfile doesn't include fastapi itself.

It's recommended to instead create a requirements.in, referencing the current project:

[venv] % pipacs '-e .[dev,test]'

If a project uses a requirements.txt already, you can use pips or envin to "sync" to that specification (without any requirements.in file). While using pip-tools' pip-sync on a non-pip-compiled requirements.txt is not currently recommended, zpy's version of "syncing" ensures the dependencies of each needed package are installed, even if not directly present in requirements.txt.