Python使用HTTP在远程文件上搜索 [英] Python seek on remote file using HTTP

问题描述

如何在远程（HTTP）文件上寻找特定位置，以便我只能下载该部分？

How do I seek to a particular position on a remote (HTTP) file so I can download only that part?

让我们说远程文件上的字节数是：1234567890

Lets say the bytes on a remote file were: 1234567890

我想寻求4并从那里下载3个字节，所以我会：456

I wanna seek to 4 and download 3 bytes from there so I would have: 456

和另外，如何检查远程文件是否存在？
我试过，os.path.isfile（）但是当我传递一个远程文件url时它返回False。

and also, how do I check if a remote file exists? I tried, os.path.isfile() but it returns False when I'm passing a remote file url.

推荐答案

如果您通过HTTP下载远程文件，则需要设置范围标题。

If you are downloading the remote file through HTTP, you need to set the Range header.

检查在此示例中如何完成。看起来像这样：

Check in this example how it can be done. Looks like this:

myUrlclass.addheader("Range","bytes=%s-" % (existSize))

编辑：我刚刚找到了更好的实施方案。这个类使用起来非常简单，因为它可以在docstring中看到。

EDIT: I just found a better implementation. This class is very simple to use, as it can be seen in the docstring.

class HTTPRangeHandler(urllib2.BaseHandler):
"""Handler that enables HTTP Range headers.

This was extremely simple. The Range header is a HTTP feature to
begin with so all this class does is tell urllib2 that the 
"206 Partial Content" reponse from the HTTP server is what we 
expected.

Example:
    import urllib2
    import byterange

    range_handler = range.HTTPRangeHandler()
    opener = urllib2.build_opener(range_handler)

    # install it
    urllib2.install_opener(opener)

    # create Request and set Range header
    req = urllib2.Request('http://www.python.org/')
    req.header['Range'] = 'bytes=30-50'
    f = urllib2.urlopen(req)
"""

def http_error_206(self, req, fp, code, msg, hdrs):
    # 206 Partial Content Response
    r = urllib.addinfourl(fp, hdrs, req.get_full_url())
    r.code = code
    r.msg = msg
    return r

def http_error_416(self, req, fp, code, msg, hdrs):
    # HTTP's Range Not Satisfiable error
    raise RangeError('Requested Range Not Satisfiable')

更新：更好的实施已移至 byterange.py中的nofollow noreferrer> github：excid3 / urlgrabber 文件。

Update: The "better implementation" has moved to github: excid3/urlgrabber in the byterange.py file.

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