Optimizing strings in Cython

Question

I\'m trying to demonstrate to our group the virtues of Cython for enhancing Python performance. I have shown several benchmarks, all that attain speed up by just:

Answer 1

I suggest you do your operations on cpython.array.arrays. The best documentation is the C API and the Cython source (see here).

from cpython cimport array

def cfuncA():
    cdef str a
    cdef int i,j
    for j in range(1000):
        a = ''.join([chr(i) for i in range(127)])

def cfuncB():
    cdef:
        str a
        array.array[char] arr, template = array.array('c')
        int i, j

    for j in range(1000):
        arr = array.clone(template, 127, False)

        for i in range(127):
            arr[i] = i

        a = arr.tostring()

Note that the operations required vary very much on what you do to your strings.

>>> python2 -m timeit -s "import pyximport; pyximport.install(); import cyytn" "cyytn.cfuncA()"
100 loops, best of 3: 14.3 msec per loop

>>> python2 -m timeit -s "import pyximport; pyximport.install(); import cyytn" "cyytn.cfuncB()"
1000 loops, best of 3: 512 usec per loop

So that's a 30x speed-up in this case.

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Also, FWIW, you can take off another fair few µs by replacing arr.tostring() with arr.data.as_chars[:len(arr)] and typing a as bytes.