unfortunately, because of the way that python3-gmpy2 has been compiled, attempting to install an older version FORCE removes (or conflicts with) an existing installation of python 3.8.
therefore if, as many people will have, they are transitioning from python 3.5 to 3.6, 3.6 to 3.7, 3.7 to 3.8, the way that python3-gmpy2 has been installed will cause serious problems, particularly if there are other dependencies... which there are: $ apt-cache rdepends python3-gmpy2 python3-gmpy2 Reverse Depends: python-gmpy2-doc python-gmpy2-common pyecm python3-ppl python3-mpmath python-gmpy2-common python3-mpmath python-gmpy2-common python3-mpmath python3-mpmath python-gmpy2-doc python-gmpy2-common i'd therefore recommend upgrading the severity of this bugreport. martin, can i suggest taking a look at this: http://deb.debian.org/debian/pool/main/n/numpy/numpy_1.17.4-5.debian.tar.xz and look at the debian/rules file. it deliberately depends on *both* python3.7 and python3.7, followed by auto-detecting the versions installed. it has heavy dependence on c compilation so should work absolutely fine # apt-get install python3-gmpy2=2.1.0~a4-1 Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: python3-gmpy2 : Depends: python3 (< 3.8) but 3.8.2-3 is to be installed E: Unable to correct problems, you have held broken packages.
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