When writing Cython code, special care must be taken to ensure that the code can be interrupted with CTRL-C. Since Cython optimizes for speed, Cython normally does not check for interrupts. For example, code like the following cannot be interrupted in Cython:
while True: pass
The cysignals package provides mechanisms to handle interrupts (and other signals and errors) in Cython code.
For changes in previous releases, see the best source available is to compare git tags: https://github.com/sagemath/cysignals/tags