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.

See http://cysignals.readthedocs.org/ for the full documentation.