python强制结束线程的那点事

　　在使用python3下载图片时， 常用的方法有urlretrieve和requests两种， 不管哪种方法在网速极慢的情况下， 会出现图片下载卡住现象。那如何解决呢？ 小编根据网上提供的资料测试了几种方法。

1、socket： 设置默认超时

　　正常下载的情况

#!/usr/bin/env python3
# -*- coding:utf-8 -*-
# __author__:kzg

import datetime
import os
from urllib.request import urlretrieve

# 函数运行计时器
def count_time(func):
    def int_time(*args, **kwargs):
        start_time = datetime.datetime.now()  # 程序开始时间
        func(*args, **kwargs)
        over_time = datetime.datetime.now()   # 程序结束时间
        total_time = (over_time-start_time).total_seconds()
        print("download picture used time %s seconds" % total_time)
    return int_time

# 下载回调函数， 计算下载进度
def callbackinfo(down, block, size):
    '''
    回调函数：
    down：已经下载的数据块
    block：数据块的大小
    size：远程文件的大小
    '''
    per = 100.0 * (down * block) / size
    if per > 100:
        per = 100
    print('%.2f%%' % per)

# 图片下载
@count_time
def downpic(url, filename):
    try:
        print("Start Down %s" % url)
        if os.path.exists(filename):
            os.remove(filename)
        urlretrieve(url, filename, callbackinfo)
    except socket.timeout as ex:
        print(ex)

url = "http://p1.meituan.net/wedding/d4c375416ab70b8b0bc4247875c929b0434138.jpg%40800w_600h_0e_1l%7Cwatermark%3D1%26%26r%3D1%26p%3D9%26x%3D2%26y%3D2%26relative%3D1%26o%3D20"
filename = r'C:\blueprint-face-detection\scripts\mv.jpg'


downpic(url, filename)


结果：
Start Down http://p1.meituan.net/wedding/d4c375416ab70b8b0bc4247875c929b0434138.jpg%40800w_600h_0e_1l%7Cwatermark%3D1%26%26r%3D1%26p%3D9%26x%3D2%26y%3D2%26relative%3D1%26o%3D20
0.00%
7.01%
14.02%
21.03%
28.04%
35.05%
42.06%
49.07%
56.08%
63.09%
70.10%
77.11%
84.12%
91.13%
98.14%
100.00%
download picture used time 0.165558 seconds

结论： 网速较快时下载完全没问题， 仅用零点几秒。

2、使用charles限制网速, 设置为下载1k/s, 上传10k/s

　　1、设置charles

　　

　　

　　2、设置socket的默认超时时间为10秒

#!/usr/bin/env python3
# -*- coding:utf-8 -*-
# __author__:kzg

import datetime
import os
import socket
from urllib.request import urlretrieve

# 函数运行计时器
def count_time(func):
    def int_time(*args, **kwargs):
        start_time = datetime.datetime.now()  # 程序开始时间
        func(*args, **kwargs)
        over_time = datetime.datetime.now()   # 程序结束时间
        total_time = (over_time-start_time).total_seconds()
        print("download picture used time %s seconds" % total_time)
    return int_time

# 下载回调函数， 计算下载进度
def callbackinfo(down, block, size):
    '''
    回调函数：
    down：已经下载的数据块
    block：数据块的大小
    size：远程文件的大小
    '''
    per = 100.0 * (down * block) / size
    if per > 100:
        per = 100
    print('%.2f%%' % per)

# 图片下载
@count_time
def downpic(url, filename):
    try:
        print("Start Down %s" % url)
        if os.path.exists(filename):
            os.remove(filename)
        urlretrieve(url, filename, callbackinfo)
    except socket.timeout as ex:
        print(ex)

url = "http://p1.meituan.net/wedding/d4c375416ab70b8b0bc4247875c929b0434138.jpg%40800w_600h_0e_1l%7Cwatermark%3D1%26%26r%3D1%26p%3D9%26x%3D2%26y%3D2%26relative%3D1%26o%3D20"
filename = r'C:\blueprint-face-detection\scripts\mv.jpg'

# 设置10秒超时
socket.setdefaulttimeout(10)
downpic(url, filename)

结果：
Start Down http://p1.meituan.net/wedding/d4c375416ab70b8b0bc4247875c929b0434138.jpg%40800w_600h_0e_1l%7Cwatermark%3D1%26%26r%3D1%26p%3D9%26x%3D2%26y%3D2%26relative%3D1%26o%3D20
timed out
download picture used time 10.013625 seconds

　　结论： 正如期望的那样， 10秒种后下载自动结束了，重试了3次， 每次都好使，  好高兴 ^_^

猜想， 那我把网速提高一些呢， 应该更好使吧！！！， 下载10k/s, 上传10k/s。

完啦， 擦擦擦， 这是什么情况， 网速提高了， 下载好久了还没结束。

 经过多次尝试发现下载设置超过4k/s时， socket设置defaulttime就不起作用了。

待叙……