如果未下载则从列表中下载文件

Question

我可以用C#来做到这一点，不过代码挺长的。

如果有人能告诉我用Python怎么做，那就太好了。

伪代码是：

url: www.example.com/somefolder/filename1.pdf

1. load file into an array (file contains a url on each line)
2. if file e.g. filename1.pdf doesn't exist, download file

这个脚本可以按照以下结构来写：

/python-downloader/
/python-downloader/dl.py
/python-downloader/urls.txt
/python-downloader/downloaded/filename1.pdf

Answer 1

在Python中代码更少，你可以用这样的方式：

import urllib2
improt os

url="http://.../"
# Translate url into a filename
filename = url.split('/')[-1]

if not os.path.exists(filename)
  outfile = open(filename, "w")
  outfile.write(urllib2.urlopen(url).read())
  outfile.close()

Answer 2

这是一个稍微修改过的WoLpH的脚本，适用于Python 3.3。

#!/usr/bin/python3.3
import os.path
import urllib.request

links = open('links.txt', 'r')
for link in links:
    link = link.strip()
    name = link.rsplit('/', 1)[-1]
    filename = os.path.join('downloads', name)

    if not os.path.isfile(filename):
        print('Downloading: ' + filename)
        try:
            urllib.request.urlretrieve(link, filename)
        except Exception as inst:
            print(inst)
            print('  Encountered unknown error. Continuing.')

Answer 3

这样做应该可以解决问题，不过我假设 urls.txt 文件里只包含网址，不包括 url: 这个前缀。

import os
import urllib

DOWNLOADS_DIR = '/python-downloader/downloaded'

# For every line in the file
for url in open('urls.txt'):
    # Split on the rightmost / and take everything on the right side of that
    name = url.rsplit('/', 1)[-1]

    # Combine the name and the downloads directory to get the local filename
    filename = os.path.join(DOWNLOADS_DIR, name)

    # Download the file if it does not exist
    if not os.path.isfile(filename):
        urllib.urlretrieve(url, filename)