  We present PyCCE, an open-source Python library to simulate the dynamics of
spin qubits in a spin bath, using the cluster-correlation expansion (CCE)
method. PyCCE includes modules to generate realistic spin baths, employing
coupling parameters computed from first principles with electronic structure
codes, and enables the user to run simulations with either the conventional or
generalized CCE method. We illustrate three use cases of the Python library:
the calculation of the Hahn-echo coherence time of the nitrogen vacancy in
diamond; the calculation of the coherence time of the basal divacancy in
silicon carbide at avoided crossings; and the magnetic field
orientation-dependent dynamics of a shallow donor in silicon.
  The complete documentation and installation instructions are available at
https://pycce.readthedocs.io/en/latest/.
