exception handling in cython
If your cdef or cpdef function or method does not declare a return type (as is normal in CPython code), then you get exceptions without any extra effort.
If your cdef or cpdef function or method declares a C-style return type, the error and exception will be handled this way:
- A plain cdef declared function, that does not return a Python object…
- Has no way of reporting a Python exception to it’s caller.
- Will only print a warning message and the exception is ignored.
- In order to propagate exceptions like this to it’s caller, you need to declare an exception value for it.
There are three forms of declaring an exception for a C compiled program.
cdef int spam() except -1: pass - In the example above, if an error occurs inside spam, it will immediately return with the value of -1, causing an exception to be propagated to it’s caller.
- Functions declared with an exception value, should explicitly prevent a return of that value.
cdef int spam() except? -1: pass - Used when a -1 may possibly be returned and is not to be considered an error.
- The “?” tells Cython that -1 only indicates a possible error.
- Now, each time -1 is returned, Cython generates a call to PyErr_Occurred to verify it is an actual error.
cdef int spam() except *: pass - A call to PyErr_Occurred happens every time the function gets called.
- A need to propagate errors when returning void must use this version.