Python爬取视频(其实是一篇福利)过程解析

窗外下着小雨，作为单身程序员的我逛着逛着发现一篇好东西，来自知乎 你都用 Python 来做什么？的第一个高亮答案。

到上面去看了看，地址都是明文的，得，赶紧开始吧。

下载流式文件，requests库中请求的stream设为True就可以啦，文档在此。

先找一个视频地址试验一下：

# -*- coding: utf-8 -*-
import requests 
def download_file(url, path):
  with requests.get(url, stream=True) as r:
    chunk_size = 1024
    content_size = int(r.headers['content-length'])
    print '下载开始'
    with open(path, "wb") as f:
      for chunk in r.iter_content(chunk_size=chunk_size):
        f.write(chunk) 
if __name__ == '__main__':
  url = '就在原帖...'
  path = '想存哪都行'
  download_file(url, path)

遭遇当头一棒：

AttributeError: __exit__

这文档也会骗人的么！

看样子是没有实现上下文需要的__exit__方法。既然只是为了保证要让r最后close以释放连接池，那就使用contextlib的closing特性好了：

# -*- coding: utf-8 -*-
import requests
from contextlib import closing
 
def download_file(url, path):
  with closing(requests.get(url, stream=True)) as r:
    chunk_size = 1024
    content_size = int(r.headers['content-length'])
    print '下载开始'
    with open(path, "wb") as f:
      for chunk in r.iter_content(chunk_size=chunk_size):
        f.write(chunk)

程序正常运行了，不过我盯着这文件，怎么大小不见变啊，到底是完成了多少了呢？还是要让下好的内容及时存进硬盘，还能省点内存是不是：

# -*- coding: utf-8 -*-
import requests
from contextlib import closing
import os
 
def download_file(url, path):
  with closing(requests.get(url, stream=True)) as r:
    chunk_size = 1024
    content_size = int(r.headers['content-length'])
    print '下载开始'
    with open(path, "wb") as f:
      for chunk in r.iter_content(chunk_size=chunk_size):
        f.write(chunk)
        f.flush()
        os.fsync(f.fileno())

文件以肉眼可见的速度在增大，真心疼我的硬盘，还是最后一次写入硬盘吧，程序中记个数就好了：

def download_file(url, path):
  with closing(requests.get(url, stream=True)) as r:
    chunk_size = 1024
    content_size = int(r.headers['content-length'])
    print '下载开始'
    with open(path, "wb") as f:
      n = 1
      for chunk in r.iter_content(chunk_size=chunk_size):
        loaded = n*1024.0/content_size
        f.write(chunk)
        print '已下载{0:%}'.format(loaded)
        n += 1

结果就很直观了：

已下载2.579129%
已下载2.581255%
已下载2.583382%
已下载2.585508%

心怀远大理想的我怎么会只满足于这一个呢，写个类一起使用吧：

# -*- coding: utf-8 -*-
import requests
from contextlib import closing
import time 
def download_file(url, path):
  with closing(requests.get(url, stream=True)) as r:
    chunk_size = 1024*10
    content_size = int(r.headers['content-length'])
    print '下载开始'
    with open(path, "wb") as f:
      p = ProgressData(size = content_size, unit='Kb', block=chunk_size)
      for chunk in r.iter_content(chunk_size=chunk_size):
        f.write(chunk)
        p.output()
 
 
class ProgressData(object):
 
  def __init__(self, block,size, unit, file_name='', ):
    self.file_name = file_name
    self.block = block/1000.0
    self.size = size/1000.0
    self.unit = unit
    self.count = 0
    self.start = time.time()
  def output(self):
    self.end = time.time()
    self.count += 1
    speed = self.block/(self.end-self.start) if (self.end-self.start)>0 else 0
    self.start = time.time()
    loaded = self.count*self.block
    progress = round(loaded/self.size, 4)
    if loaded >= self.size:
      print u'%s下载完成\r\n'%self.file_name
    else:
      print u'{0}下载进度{1:.2f}{2}/{3:.2f}{4} 下载速度{5:.2%} {6:.2f}{7}/s'.\
         format(self.file_name, loaded, self.unit,\
         self.size, self.unit, progress, speed, self.unit)
      print '%50s'%('/'*int((1-progress)*50))

运行：

下载开始
下载进度10.24Kb/120174.05Kb 0.01% 下载速度4.75Kb/s
/////////////////////////////////////////////////
下载进度20.48Kb/120174.05Kb 0.02% 下载速度32.93Kb/s
/////////////////////////////////////////////////

看上去舒服多了。

下面要做的就是多线程同时下载了，主线程生产url放入队列，下载线程获取url：

# -*- coding: utf-8 -*-
import requests
from contextlib import closing
import time
import Queue
import hashlib
import threading
import os 
def download_file(url, path):
  with closing(requests.get(url, stream=True)) as r:
    chunk_size = 1024*10
    content_size = int(r.headers['content-length'])
    if os.path.exists(path) and os.path.getsize(path)>=content_size:
      print '已下载'
      return
    print '下载开始'
    with open(path, "wb") as f:
      p = ProgressData(size = content_size, unit='Kb', block=chunk_size, file_name=path)
      for chunk in r.iter_content(chunk_size=chunk_size):
        f.write(chunk)
        p.output()
 
class ProgressData(object):
 
  def __init__(self, block,size, unit, file_name='', ):
    self.file_name = file_name
    self.block = block/1000.0
    self.size = size/1000.0
    self.unit = unit
    self.count = 0
    self.start = time.time()
  def output(self):
    self.end = time.time()
    self.count += 1
    speed = self.block/(self.end-self.start) if (self.end-self.start)>0 else 0
    self.start = time.time()
    loaded = self.count*self.block
    progress = round(loaded/self.size, 4)
    if loaded >= self.size:
      print u'%s下载完成\r\n'%self.file_name
    else:
      print u'{0}下载进度{1:.2f}{2}/{3:.2f}{4} {5:.2%} 下载速度{6:.2f}{7}/s'.\
         format(self.file_name, loaded, self.unit,\
         self.size, self.unit, progress, speed, self.unit)
      print '%50s'%('/'*int((1-progress)*50))
 queue = Queue.Queue() 
def run():
  while True:
    url = queue.get(timeout=100)
    if url is None:
      print u'全下完啦'
      break
    h = hashlib.md5()
    h.update(url)
    name = h.hexdigest()
    path = 'e:/download/' + name + '.mp4'
    download_file(url, path) 
def get_url():
  queue.put(None)
if __name__ == '__main__':
  get_url()
  for i in xrange(4):
    t = threading.Thread(target=run)
    t.daemon = True
    t.start()

加了重复下载的判断，至于怎么源源不断的生产url，诸位摸索吧，保重身体！

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