Cython C-Type definition

Question

To make my Cython code more faster, I like to declare variable types as much as possible.

cpdef void __init__(self, config, protocol=None, int slave_number, int fifo_length=170, float speed_factor=1.0) except *:
        assert 0 < config.watermark_height <= fifo_length
        assert protocol is None
        assert slave_number is int
        self.config = config
        self.protocol = protocol
        self.slave_number = slave_number
        self.speed_factor = speed_factor

2 questions:

1. How do I declare the self.slave_number variable as int?#

2. Is the assertion (e.g. slave_numbers is int) unnecessary if I cp-function parameter already says its an int?

Thank you!

Answer 1

1. The variables from the Extension type are defined in the class declaration. In your situation:

   cdef class SpeedClass:
       cdef int slave_number
       cdef ...
   

2. A call to __init__ will cast the argument to an integer and error when the operation is impossible. You can thus pass a floating point value to the function. From inside the function, slave_numbers is always an integer as it will have been casted at call-time anyway and the check is useless. I couldn't find this information explicitly in the docs so I have tested it with a small example (see below).

   def f1(int i):
       print(type(i))
       return i*2
   

   that you can test from the command line as

   python3 -c 'import test_arguments; print(test_arguments.f1(1))'
   

   or

   python3 -c 'import test_arguments; print(test_arguments.f1(1.23))'