web3-starter-py/web3-toolkit/cython/README.md

Cython

tl; dr

• cython is an optimising static compiler for both Python and the extended cython programming language, making writing C extensions for Python easier.
• it turns readable Python code into plain C performance by adding static type declarations in Python syntax.
• cython source file names consist of the name of the module followed by a .pyx extension.
• the setuptools extension provided with cython allows you to pass .pyx files directly to the Extension constructor in the setup file.
• to compile the extension for use in the current directory, you can use python setup.py build_ext --inplace

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cythonize example

• for typing variables, consider the following snippet in python:

def f(x):
    return x ** 2- x

def integrate_f(a, b, N):

    s = 0
    dx = (b - a) / N
    for i in range(N):
        s += f(a + i * dx)

    return s * dx

• compiling this in cython already gives a ~35% speedup, but adding static types can make it up to 4x faster.
• to accomplish this, you can add type declarations, for example:

def f(x: cython.double):
    return x ** 2 - x

def integrate_f(a: cython.double, b: cython.double, N: cython.int):

    i: cython.int
    s: cython.double
    dx: cython.double
    s = 0
    dx = (b - a) / N
    for i in range(N):
        s += f(a + i * dx)

    return s * dx

• this is converted to cython as pure C-style code:

def f(double x):
    return x ** 2 - x

def integrate_f(double a, double b, int N):

    cdef int i
    cdef double s
    cdef double dx
    s = 0
    dx = (b - a) / N
    for i in range(N):
        s += f(a + i * dx)

    return s * dx

• since python functions can be expensive, the cython specific cdef statement, as well as @cfunc decorator can be used:

cdef double f(double x) except? -2:
    return x ** 2 -x