Since Cython mixes C and Python semantics, some things may be a bit surprising or unintuitive. Work always goes on to make Cython more natural for Python users, so this list may change in the future.

  • 10**-2 == 0, instead of 0.01 like in Python.
  • Given two typed int variables a and b, a % b has the same sign as the second argument (following Python semantics) rather than having the same sign as the first (as in C). The C behavior can be obtained, at some speed gain, by enabling the cdivision directive (versions prior to Cython 0.12 always followed C semantics).
  • Care is needed with unsigned types. cdef unsigned n = 10; print(range(-n, n)) will print an empty list, since -n wraps around to a large positive integer prior to being passed to the range function.
  • Python’s float type actually wraps C double values, and the int type in Python 2.x wraps C long values.

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