cython3 binary package in Ubuntu Xenial s390x

 Cython is a language that makes writing C extensions for the Python language as
 easy as Python itself. Cython is based on the well-known Pyrex, but supports
 more cutting edge functionality and optimizations.
 .
 The Cython language is very close to the Python language, but Cython
 additionally supports calling C functions and declaring C types on variables
 and class attributes. This allows the compiler to generate very efficient C
 code from Cython code.
 .
 This makes Cython the ideal language for wrapping external C libraries, and
 for fast C modules that speed up the execution of Python code.

Source package