Question

According to the urllib2 documentation,

Because the default handlers handle redirects (codes in the 300 range), and codes in the 100-299 range indicate success, you will usually only see error codes in the 400-599 range.

And yet the following code

request = urllib2.Request(url, data, headers)
response = urllib2.urlopen(request)

raises an HTTPError with code 201 (created):

ERROR    2011-08-11 20:40:17,318 __init__.py:463] HTTP Error 201: Created

So why is urllib2 throwing HTTPErrors on this successful request?

It’s not too much of a pain; I can easily extend the code to:

try:
    request = urllib2.Request(url, data, headers)
    response = urllib2.urlopen(request)
except HTTPError, e:
    if e.code == 201:
        # success! :)
    else:
        # fail! :(
else:
    # when will this happen...?

But this doesn’t seem like the intended behavior, based on the documentation and the fact that I can’t find similar questions about this odd behavior.

Also, what should the else block be expecting? If successful status codes are all interpreted as HTTPErrors, then when does urllib2.urlopen() just return a normal file-like response object like all the urllib2 documentation refers to?

Answer 1

As the actual library documentation mentions:

For 200 error codes, the response object is returned immediately.

For non-200 error codes, this simply passes the job on to the protocol_error_code handler methods, via OpenerDirector.error(). Eventually, urllib2.HTTPDefaultErrorHandler will raise an HTTPError if no other handler handles the error.

http://docs.python.org/library/urllib2.html#httperrorprocessor-objects