Python多线程求和程序

今天写了一个Python的多线程求和程序。满足以下要求：

1、可以设置步长

2、步长可为负

3、支持小数

4、可指定线程数

5、处理各种无效输入

程序如下：

import threading
from math import ceil

result = 0
def sub_sum(start, end, step):
    global result
    sum = float(0)
    temp = start
    while temp < end + step / 1000000:
        sum += temp
        temp += step
    #print("sum from %f to %f by the step %f is %f"\
    #        % (start, end, step, sum))
    result += sum

def thread_sum(start, end, step = 1, num_thread = 1):
    global result

    num_threads = int(num_thread)
    if (num_threads <= 0):
        num_threads = 1
    end = start + int((end - start)/step) * step

    numbers = end - start
    if (numbers < 0 and step > 0) or (numbers > 0 and step < 0):
        print("error in sum: from %f to %f by the step %f is invalid."\
                % (start, end, step))
        return 0
    elif numbers == 0:
        return start
    if numbers < 0:
        (start, end, step) = (end, start, -step)
        numbers *= -1
    d = ceil(numbers / num_thread / step) * step
    if d < step:
        d = step
    begin = 0
    threads = []
    while start + begin * d < end:
        threads.append(threading.Thread(target=sub_sum,\
                args=(start + d * begin,\
                    start + d * (begin + 1) - step \
                        if start + (begin + 1) * d < end else end,\
                    step)))
        begin += 1

    print("Actual threads count: %d" % len(threads))
    for i in range(len(threads)):
        threads[i].start()
    for i in range(len(threads)):
        threads[i].join()
    return result

if __name__ == "__main__":
    start = raw_input("Please input the start: ")
    end = raw_input("Please input the end: ")
    step = raw_input("Please input the step(default 1): ")

    start = float(start)
    end = float(end)
    step = 1 if step == "" else float(step)

    num_thread = raw_input("Please input the num of threads: ")
    num_thread = int(num_thread)
    if num_thread < 0:
        print("The num_thread must be positive but not %d" % num_thread)
        exit(0)
    print("Ths sum is: %f" % thread_sum(start, end, step, num_thread))

    s = 0
    if start < end and step > 0:
        while start <= end:
            s += start
            start += step
    elif start > end and step < 0:
        while start >= end:
            s += start
            start += step
    print("normal function: %s" % s)