the better tailcall-optimizer for python 2.7 by mokrates

# tail-call-optimizer
# the betterrerer version

# no tailcall-marker needed anymore. this finds the tailcall in the bytecode by itself
# (in this example only CALL_FUNCTION, but this can easily extended to
# CALL_FUNCTION_KW, CALL_FUNCTION_VAR and CALL_FUNCTION_KW_VAR

# written by mokrates

import dis
import new

def modify_assembler(codestring):
    codelist = [ord(c) for c in codestring]

    # filter CALL_FUNCTION
    for i in xrange(0,len(codelist)-4):
        if (codelist[i] == dis.opmap['CALL_FUNCTION'] and
            codelist[i+3] == dis.opmap['RETURN_VALUE'] ):
            codelist[i] = dis.opmap['BUILD_TUPLE']
            codelist[i+1] = codelist[i+1] + 1

    return reduce(str.__add__, ( chr(x) for x in codelist ))

def recreate_modified_func(func):
    code_cl = func.func_code.__class__
    function_cl = func.__class__

    f=func.func_code

    codestring=modify_assembler(f.co_code)

    code = new.code(f.co_argcount, f.co_nlocals, f.co_stacksize, f.co_flags, codestring,
        f.co_consts, f.co_names,
            f.co_varnames, f.co_filename, f.co_name, f.co_firstlineno, f.co_lnotab)

    newfunc = new.function(code, func.func_globals, func.func_name, func.func_defaults, func.func_closure)

    return newfunc

def tailopt(f):
    def taildecor(*args, **kwargs):
        res = mod_f(*args, **kwargs)
        while (isinstance(res, tuple) and
            len(res) > 0 and
            callable(res[0])):

            if ('_taildecor_mod_f' in dir(res[0])):
                res = res[0]._taildecor_mod_f(*res[1:])
            else:
                return res[0](*res[1:])

        return res

    mod_f = recreate_modified_func(f)
    taildecor._taildecor_mod_f = mod_f
    return taildecor

if __name__ == '__main__':

    # example

    @tailopt
    def fak(still, acc=1):
        if (still==1): return str(acc)
        else: return fak(still-1, acc * still)

    print fak(10000)

    # alternating tailcall

    @tailopt
    def fak1(still, acc=1):
        if (still==1): return str(acc)
        else: return fak2(still-1, acc * still)

    @tailopt
    def fak2(still, acc=1):
        if (still==1): return str(acc)
        else: return fak1(still-1, acc * still)

    print fak1(10000)