Want to read from a particular offset of a file fr

问题:

I want to read a file on internet from a particular offset in python. Like in normal file handler (return by open()) we have a seek() api. Is there any way of doing this when reading from network.

import urllib.request
g = urllib.request.urlopen('http://tools.ietf.org/rfc/rfc2822.txt')
g.seek(20)
f=g.read(100)
print(f)

I tried the following but it obviosuly gave error

io.UnsupportedOperation: seek

What can I do to solve this?

回答1:

You can use Range header (only if the server supports it):

import urllib.request
req = urllib.request.Request('http://tools.ietf.org/rfc/rfc2822.txt',
                             headers={'Range': 'bytes=20-'})
g = urllib.request.urlopen(req)
f = g.read(100)
print(f)

But not all server support Range. You should check response header. If server does not support it, you should skip bytes by read them.

import urllib.request
req = urllib.request.Request('http://tools.ietf.org/rfc/rfc2822.txt',
                             headers={'Range': 'bytes=20-'})
g = urllib.request.urlopen(req)
if 'Content-Range' not in g.info(): # <-----
# OR  if g.status != http.client.PARTIAL_CONTENT
    g.read(20)                      # <-----
f = g.read(100)
print(f)