利用Python下载文件

利用Python下载文件也是十分方便的：

小文件下载

下载小文件的话考虑的因素比较少，给了链接直接下载就好了：

import requests
image_url = "https://www.python.org/static/community_logos/python-logo-master-v3-TM.png"

r = requests.get(image_url) # create HTTP response object

with open("python_logo.png",'wb') as f:
    f.write(r.content)

大文件下载

如果是小文件的话，一次性下载就OK了，但是如果文件比较大的话，那么下载下来的文件先放在内存中，内存还是比较有压力的。所以为了防止内存不够用的现象出现，我们要想办法把下载的文件分块写到磁盘中：

import requests

file_url = "http://codex.cs.yale.edu/avi/db-book/db4/slide-dir/ch1-2.pdf"

r = requests.get(file_url, stream=True)

with open("python.pdf", "wb") as pdf:
for chunk in r.iter_content(chunk_size=1024):
if chunk:
            pdf.write(chunk)

批量文件下载：

批量文件下载的思路也很简单，首先读取网页的内容，再从网页中抽取链接信息，比如通过a标签，然后再从抽取出的链接中过滤出我们想要的链接，比如在本例中，我们只想下载MP4文件，那么我们可以通过文件名过滤所有链接：

import requests
from bs4 import BeautifulSoup

archive_url = "http://www-personal.umich.edu/~csev/books/py4inf/media/"


def get_video_links():
    r = requests.get(archive_url)
    soup = BeautifulSoup(r.content, 'html5lib')
    links = soup.findAll('a')
    video_links = [archive_url + link['href'] for link in links if link['href'].endswith('mp4')]

return video_links


def download_video_series(video_links):
for link in video_links:
        file_name = link.split('/')[-1]

        print("Downloading file:%s" % file_name)
        r = requests.get(link, stream=True)

# download started
with open(file_name, 'wb') as f:
for chunk in r.iter_content(chunk_size=1024 * 1024):
if chunk:
                    f.write(chunk)

        print("%s downloaded!\n" % file_name)


    print("All videos downloaded!")

return


if __name__ == "__main__":
    video_links = get_video_links()
    download_video_series(video_links)