Installation is easy. Checkout the Git repository of RETURNN ( Install all dependencies, which are just numpy, h5py, and the backend you want to use (TensorFlow or Theano). You can do so via:

pip install -r requirements.txt

You might want to use pip3 instead of pip, and you also might want to add the option --user (if you are not using virtualenv).

For TensorFlow, use pip install tensorflow, and for PyTorch, use pip install torch torchdata torchaudio.

For some specific datasets or special layers, additional dependencies might be needed, such as librosa. For running the tests, you need pytest and nose.

You can also install RETURNN as a framework, via pip (PyPI entry), like:

pip install returnn

See Basic Usage for the basic usage of RETURNN.