It is a known issue with Python 3.8.3rc1. See https://bugs.python.org/issue39562 for details.
- Bug#960201: python-gmpy2: autopkgtest regressio... Paul Gevers
- Bug#960201: python-gmpy2: autopkgtest regr... Martin Kelly
- Bug#960201: python-gmpy2: autopkgtest ... Paul Gevers
- Bug#960201: python-gmpy2: autopkgt... Case Van Horsen
- Bug#960201: Update Case Van Horsen
- Bug#960201: marked as done (python-gmpy2: ... Debian Bug Tracking System
