This is a regression caused by the new HTTPStatus enum from Issue 21793. RFC 6585 uses the plural “Fields”, so maybe the new enum symbol needs renaming.

$ python3.4
Python 3.4.2 (default, Oct  8 2014, 13:44:52) 
[GCC 4.9.1 20140903 (prerelease)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import http.client
>>> http.client.REQUEST_HEADER_FIELDS_TOO_LARGE
431
>>> http.client.REQUEST_HEADER_FIELD_TOO_LARGE
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: 'module' object has no attribute 'REQUEST_HEADER_FIELD_TOO_LARGE'
>>> 
$ ./python
Python 3.5.0a0 (qbase qtip simple-http-testing.patch tip:f3fadbfb10ba, Feb 11 2015, 07:18:07) 
[GCC 4.9.1] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import http.client
>>> http.client.REQUEST_HEADER_FIELDS_TOO_LARGE
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: module 'http.client' has no attribute 'REQUEST_HEADER_FIELDS_TOO_LARGE'
>>> http.client.REQUEST_HEADER_FIELD_TOO_LARGE
<HTTPStatus.REQUEST_HEADER_FIELD_TOO_LARGE: 431>

Thanks for the catch Martin, the field should indeed be updated to be
plural. I'll try to get a patch for this later today unless someone else
beats me to it

The attached patch fixes the name

Thanks. Confirming the patch fixes the problem for me, so should be comitted. I wonder if a test case would be good too though.

I found another regression: In Python 3.4, 416 is REQUESTED_RANGE_NOT_SATISFIABLE, but REQUEST_RANGE_NOT_SATISFIABLE in 3.5.

Here is a test case.

======================================================================
FAIL: test_client_constants (test.test_httplib.OfflineTest) (constant='REQUESTED_RANGE_NOT_SATISFIABLE')
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/berker/projects/cpython/default/Lib/test/test_httplib.py", line 985, in test_client_constants
    self.assertTrue(hasattr(client, const))
AssertionError: False is not true

======================================================================
FAIL: test_client_constants (test.test_httplib.OfflineTest) (constant='REQUEST_HEADER_FIELDS_TOO_LARGE')
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/berker/projects/cpython/default/Lib/test/test_httplib.py", line 985, in test_client_constants
    self.assertTrue(hasattr(client, const))
AssertionError: False is not true

Thanks for the test Berker, I'll put a patch together with the changes
later this afternoon.

On 2015-02-12 2:27 PM, Berker Peksag wrote:
> 
> Berker Peksag added the comment:
> 
> Here is a test case.
> 
> ======================================================================
> FAIL: test_client_constants (test.test_httplib.OfflineTest) (constant='REQUESTED_RANGE_NOT_SATISFIABLE')
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>   File "/home/berker/projects/cpython/default/Lib/test/test_httplib.py", line 985, in test_client_constants
>     self.assertTrue(hasattr(client, const))
> AssertionError: False is not true
> 
> ======================================================================
> FAIL: test_client_constants (test.test_httplib.OfflineTest) (constant='REQUEST_HEADER_FIELDS_TOO_LARGE')
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>   File "/home/berker/projects/cpython/default/Lib/test/test_httplib.py", line 985, in test_client_constants
>     self.assertTrue(hasattr(client, const))
> AssertionError: False is not true
> 
> ----------
> Added file: http://bugs.python.org/file38119/httpstatus_tests.diff
> 
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue23442>
> _______________________________________
>

I've attached a patch with fixes for both cases and the tests added by
Berker. Thanks guys.

New changeset 52d37efaf939 by Berker Peksag in branch 'default':
Issue #23442: Rename two member names to stay backward compatible
https://hg.python.org/cpython/rev/52d37efaf939

Fixed. Thanks to both of you :)