If you are using pip, you can simply run
pip install symfit
from your terminal. If you prefer to use conda, run
conda install -c conda-forge symfit
instead. Lastly, if you prefer to install manually you can download the source from https://github.com/tBuLi/symfit.
To also install the dependencies of 3rd party contrib modules such as interactive guesses, install symfit using:
pip install symfit[contrib]
See requirements.txt for a full list.