  The observation of cosmic microwave background (CMB) anisotropies is one of
the key probes of physical cosmology. The weak nature of this signal has driven
the construction of increasingly complex and sensitive experiments observing
the sky at multiple frequencies with thousands of polarization sensitive
detectors. Given the high sensitivity of such experiments, instrumental
systematic effects can become the limiting factor towards the full scientific
exploitation of their data. In this paper we present s4cmb (Systematics for
CMB), a Python package designed to simulate raw data streams in time domain of
modern CMB experiments based on bolometric technology, and to inject in these
realistic instrumental systematics effects. The aim of the package is to help
assessing the contamination due to instrumental systematic effects on real
data, to guide the design of future instruments, as well as to increase the
realism of simulated data sets required in the development of accurate data
analysis methods.
