  Gravitational waves in the sensitivity band of ground-based detectors can be
emitted by a number of astrophysical sources, including not only binary
coalescences, but also individual spinning neutron stars. The most promising
signals from such sources, although not yet detected, are long-lasting,
quasi-monochromatic Continuous Waves (CWs). The PyFstat package provides tools
to perform a range of CW data-analysis tasks. It revolves around the
F-statistic, a matched-filter detection statistic for CW signals that has been
one of the standard methods for LIGO-Virgo CW searches for two decades. PyFstat
is built on top of established routines in LALSuite but through its more modern
Python interface it enables a flexible approach to designing new search
strategies. Hence, it serves a dual function of (i) making LALSuite CW
functionality more easily accessible through a Python interface, thus
facilitating the new user experience and, for developers, the exploratory
implementation of novel methods; and (ii) providing a set of production-ready
search classes for use cases not yet covered by LALSuite itself, most notably
for MCMC-based followup of promising candidates from wide-parameter-space
searches.
