Cython Function Declarations¶
Cython supports three ways of declaring functions using the keywords:
def - Basically, it’s Python¶
def is used for code that will be:
- Called directly from Python code with Python objects as arguments.
- Returns a Python object.
The generated code treats every operation as if it was dealing with Python objects with Python consequences so it incurs a high overhead.
def is safe to use with no gotchas. Declaring the types of arguments and local types (thus return values) can allow Cython to generate optimised code which speeds up the execution. If the types are declared then a
TypeError will be raised if the function is passed the wrong types.
cdef - Basically, it’s C¶
cdef is used for Cython functions that are intended to be pure ‘C’ functions. All types must be declared. Cython aggressively optimises the the code and there are a number of gotchas. The generated code is about as fast as you can get though.
cdef declared functions are not visible to Python code that imports the module.
Take some care with
cdef declared functions; it looks like you are writing Python but actually you are writing C.
cpdef - It’s Both¶
cpdef functions combine both
cdef by creating two functions; a
cdef for C types and a
def fr Python types. This exploits early binding so that
cpdef functions may be as fast as possible when using C fundamental types (by using
cpdef functions use dynamic binding when passed Python objects and this might much slower, perhaps as slow as
def declared functions.