python - How to call urllib2 get_header method?

Question

I was looking into python urllib2 download size question.

Although the method RanRag or jterrace suggested worked fine for me but I was wondering how to use the urllib2.Request.get_header method to achieve the same. So, I tried the below line of code:

>>> import urllib2
>>> req_info = urllib2.Request('http://mirror01.th.ifl.net/releases//precise/ubuntu-12.04-desktop-i386.iso')
>>> req_info.header_items()
[]
>>> req_info.get_header('Content-Length')
>>>

As, you can see the get_header returned nothing and neither does header_items.

So, what is the correct way to use the above methods?

Answer 1

The urllib2.Request class is just "an abstraction of a URL request" (http://docs.python.org/library/urllib2.html#urllib2.Request), and does not do any actual retrieval of data. You must use urllib2.urlopen to retrieve data. urlopen either takes the url directly as a string, or you can pass an instance of the Request object too.

For example:

>>> req_info = urllib2.urlopen('https://www.google.com/logos/2012/javelin-2012-hp.jpg')
>>> req_info.headers.keys()
['content-length', 'x-xss-protection', 'x-content-type-options', 'expires', 'server', 'last-modified', 'connection', 'cache-control', 'date', 'content-type']
>>> req_info.headers.getheader('Content-Length')
'52741'