Cython: Fastest way to convert char value to string

Question

I need to convert multiple char values to strings of corresponding ASCII characters as fast as possible. Here is a toy example. I want H() function, called from python environment, to return str 'aaa'.

from libcpp.string cimport string

cdef string G():
   return chr(97)

def H():
    cdef string s
    s.append(G())
    s.append(G())
    s.append(G())

    return s

I believe, this is not optimal variant, since it uses python function ord() which boxes 97 into python object, then returns char, boxes it into another python object str and finally converts it into c++ string. How could I do the conversion faster?

This is a toy example. I need to convert arbitrary byte values to corresponding ASCII characters and concatenate them in one string. — Apogentus, Feb 15 '14 at 09:43

score 3 · Accepted Answer · answered Feb 15 '14 at 14:44

Found it!

<string>chr(i)

may be replaced by

string(1, <char>i)

Here is an example of new variant:

cdef string G():
    return string(1,<char>97)


def H():
    cdef string s
    s.append(G())
    s.append(G())
    s.append(G())
    return s

New variant works 2 times faster.

Cython: Fastest way to convert char value to string

1 Answers1