Symbolic Implementation of Extensions of the $\texttt{PyCosmo}$
  Boltzmann Solver
  $\texttt{PyCosmo}$ is a Python-based framework for the fast computation of
cosmological model predictions. One of its core features is the symbolic
representation of the Einstein-Boltzmann system of equations. Efficient
$\texttt{C/C++}$ code is generated from the $\texttt{SymPy}$ symbolic
expressions making use of the $\texttt{sympy2c}$ package. This enables easy
extensions of the equation system for the implementation of new cosmological
models. We illustrate this with three extensions of the $\texttt{PyCosmo}$
Boltzmann solver to include a dark energy component with a constant equation of
state, massive neutrinos and a radiation streaming approximation. We describe
the $\texttt{PyCosmo}$ framework, highlighting new features, and the symbolic
implementation of the new models. We compare the $\texttt{PyCosmo}$ predictions
for the $\Lambda$CDM model extensions with $\texttt{CLASS}$, both in terms of
accuracy and computational speed. We find a good agreement, to better than 0.1%
when using high-precision settings and a comparable computational speed. Links
to the Python Package Index (PyPI) page of the code release and to the PyCosmo
Hub, an online platform where the package is installed, are available at:
https://cosmology.ethz.ch/research/software-lab/PyCosmo.html.
