homepage

→ ./python.exe -V
Python 3.4.2rc1+
→ hg tip
changeset: 92532:6dcc96fa3970
tag: tip
parent: 92530:ad45c2707006
parent: 92531:8eb4eec8626c
user: Benjamin Peterson <benjamin@python.org>
date: Mon Sep 22 22:44:21 2014 -0400
summary: merge 3.4 (#22459)
When working on issue #5550, I realized that some tests are currently failing.
Here the log of running:
→ ./python.exe -m unittest -v Lib/test/test_urllib2net.py 
test_close (Lib.test.test_urllib2net.CloseSocketTest) ... ok
test_custom_headers (Lib.test.test_urllib2net.OtherNetworkTests) ... FAIL
test_file (Lib.test.test_urllib2net.OtherNetworkTests) ... test_ftp (Lib.test.test_urllib2net.OtherNetworkTests) ... skipped "Resource 'ftp://gatekeeper.research.compaq.com/pub/DEC/SRC/research-reports/00README-Legal-Rules-Regs' is not available"
test_redirect_url_withfrag (Lib.test.test_urllib2net.OtherNetworkTests) ... ok
test_sites_no_connection_close (Lib.test.test_urllib2net.OtherNetworkTests) ... ok
test_urlwithfrag (Lib.test.test_urllib2net.OtherNetworkTests) ... ok
test_ftp_basic (Lib.test.test_urllib2net.TimeoutTest) ... ok
test_ftp_default_timeout (Lib.test.test_urllib2net.TimeoutTest) ... ok
test_ftp_no_timeout (Lib.test.test_urllib2net.TimeoutTest) ... ok
test_ftp_timeout (Lib.test.test_urllib2net.TimeoutTest) ... ok
test_http_basic (Lib.test.test_urllib2net.TimeoutTest) ... ok
test_http_default_timeout (Lib.test.test_urllib2net.TimeoutTest) ... ok
test_http_no_timeout (Lib.test.test_urllib2net.TimeoutTest) ... ok
test_http_timeout (Lib.test.test_urllib2net.TimeoutTest) ... ok
======================================================================
ERROR: test_file (Lib.test.test_urllib2net.OtherNetworkTests) (url='file:/Users/karl/code/cpython/%40test_61795_tmp')
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/Users/karl/code/cpython/Lib/test/test_urllib2net.py", line 243, in _test_urls
 f = urlopen(url, req, TIMEOUT)
 File "/Users/karl/code/cpython/Lib/test/test_urllib2net.py", line 33, in wrapped
 return _retry_thrice(func, exc, *args, **kwargs)
 File "/Users/karl/code/cpython/Lib/test/test_urllib2net.py", line 23, in _retry_thrice
 return func(*args, **kwargs)
 File "/Users/karl/code/cpython/Lib/urllib/request.py", line 447, in open
 req = Request(fullurl, data)
 File "/Users/karl/code/cpython/Lib/urllib/request.py", line 267, in __init__
 origin_req_host = request_host(self)
 File "/Users/karl/code/cpython/Lib/urllib/request.py", line 250, in request_host
 host = _cut_port_re.sub("", host, 1)
TypeError: expected string or buffer
======================================================================
ERROR: test_file (Lib.test.test_urllib2net.OtherNetworkTests) (url=('file:///nonsensename/etc/passwd', None, <class 'urllib.error.URLError'>))
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/Users/karl/code/cpython/Lib/test/test_urllib2net.py", line 243, in _test_urls
 f = urlopen(url, req, TIMEOUT)
 File "/Users/karl/code/cpython/Lib/test/test_urllib2net.py", line 33, in wrapped
 return _retry_thrice(func, exc, *args, **kwargs)
 File "/Users/karl/code/cpython/Lib/test/test_urllib2net.py", line 23, in _retry_thrice
 return func(*args, **kwargs)
 File "/Users/karl/code/cpython/Lib/urllib/request.py", line 447, in open
 req = Request(fullurl, data)
 File "/Users/karl/code/cpython/Lib/urllib/request.py", line 267, in __init__
 origin_req_host = request_host(self)
 File "/Users/karl/code/cpython/Lib/urllib/request.py", line 250, in request_host
 host = _cut_port_re.sub("", host, 1)
TypeError: expected string or buffer
======================================================================
FAIL: test_custom_headers (Lib.test.test_urllib2net.OtherNetworkTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/Users/karl/code/cpython/Lib/test/test_urllib2net.py", line 186, in test_custom_headers
 self.assertEqual(request.get_header('User-agent'), 'Test-Agent')
AssertionError: 'Python-urllib/3.4' != 'Test-Agent'
- Python-urllib/3.4
+ Test-Agent
----------------------------------------------------------------------
Ran 16 tests in 124.879s
FAILED (failures=1, errors=2, skipped=1)

ok let's see
→ ./python.exe -m unittest -v Lib.test.test_urllib2net.OtherNetworkTests.test_custom_headers
test_custom_headers (Lib.test.test_urllib2net.OtherNetworkTests) ... FAIL
======================================================================
FAIL: test_custom_headers (Lib.test.test_urllib2net.OtherNetworkTests)
----------------------------------------------------------------------
Traceback (most recent call last):
 File "/Users/karl/code/cpython/Lib/test/test_urllib2net.py", line 186, in test_custom_headers
 self.assertEqual(request.get_header('User-agent'), 'Test-Agent')
AssertionError: 'Python-urllib/3.4' != 'Test-Agent'
- Python-urllib/3.4
+ Test-Agent
----------------------------------------------------------------------
Ran 1 test in 0.551s
FAILED (failures=1)
→ ./python.exe
Python 3.4.2rc1+ (3.4:8eb4eec8626c+, Sep 23 2014, 21:53:11) 
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.51)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import urllib.request
>>> url = 'http://127.0.0.1/'
>>> opener = urllib.request.build_opener()
>>> request = urllib.request.Request(url)
>>> request.header_items()
[]
>>> request.headers
{}
>>> request.add_header('User-Agent', 'Test-Agent')
>>> request.headers
{'User-agent': 'Test-Agent'}
>>> request.header_items()
[('User-agent', 'Test-Agent')]
>>> opener.open(request)
<http.client.HTTPResponse object at 0x10c0aedc0>
>>> request.get_header('User-agent'), 'Test-Agent'
('Test-Agent', 'Test-Agent')
>>> request.header_items()
[('User-agent', 'Test-Agent'), ('Host', '127.0.0.1')]
>>> request.headers
{'User-agent': 'Test-Agent'}
OK so far so good.
And my server recorded 
127.0.0.1 - - [24/Sep/2014:17:07:41 +0900] "GET / HTTP/1.1" 200 9897 "-" "Test-Agent"
Let's do it the way, the test has been designed.
→ ./python.exe
Python 3.4.2rc1+ (3.4:8eb4eec8626c+, Sep 23 2014, 21:53:11) 
[GCC 4.2.1 Compatible Apple LLVM 6.0 (clang-600.0.51)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import urllib.request
>>> url = 'http://127.0.0.1/'
>>> opener = urllib.request.build_opener()
>>> request = urllib.request.Request(url)
>>> request.header_items()
[]
>>> opener.open(request)
<http.client.HTTPResponse object at 0x10e05aa80>
>>> request.header_items()
[('User-agent', 'Python-urllib/3.4'), ('Host', '127.0.0.1')]
>>> request.has_header('User-agent')
True
>>> request.add_header('User-Agent', 'Test-Agent')
>>> opener.open(request)
<http.client.HTTPResponse object at 0x10e05ab50>
>>> request.get_header('User-agent'), 'Test-Agent'
('Python-urllib/3.4', 'Test-Agent')
>>> request.add_header('Foo', 'bar')
>>> request.header_items()
[('User-agent', 'Test-Agent'), ('Host', '127.0.0.1'), ('Foo', 'bar')]
>>> opener.open(request)
<http.client.HTTPResponse object at 0x10e05ad58>
>>> request.header_items()
[('User-agent', 'Test-Agent'), ('Host', '127.0.0.1'), ('Foo', 'bar')]
>>> request.get_header('User-agent'), 'Test-Agent'
('Python-urllib/3.4', 'Test-Agent')
>>> request.headers
{'User-agent': 'Test-Agent', 'Foo': 'bar'}
And the server recorded.
127.0.0.1 - - [24/Sep/2014:17:12:52 +0900] "GET / HTTP/1.1" 200 9897 "-" "Python-urllib/3.4"
127.0.0.1 - - [24/Sep/2014:17:12:52 +0900] "GET / HTTP/1.1" 200 9897 "-" "Python-urllib/3.4"
127.0.0.1 - - [24/Sep/2014:17:14:15 +0900] "GET / HTTP/1.1" 200 9897 "-" "Python-urllib/3.4"
So it seems that User-Agent is immutable once it has been set the first time. Not in the same dictionary.
>>> request.unredirected_hdrs
{'User-agent': 'Python-urllib/3.4', 'Host': '127.0.0.1'}

Ah! the User-Agent (or anything which is in unredirected_hdrs) will not be updated if it has already been set once. 
https://hg.python.org/cpython/file/064f6baeb6bd/Lib/urllib/request.py#l1154
>>> headers = dict(request.unredirected_hdrs)
>>> headers
{'User-agent': 'Python-urllib/3.4', 'Host': '127.0.0.1'}
>>> request.headers
{'User-agent': 'Test-Agent', 'Foo': 'cool'}
>>> headers.update(dict((k, v) for k, v in request.headers.items() if k not in headers))
>>> headers
{'User-agent': 'Python-urllib/3.4', 'Host': '127.0.0.1', 'Foo': 'cool'}

I suspect that you have your interpreters confused. (For e.g, I see 3.4 run against the trunk and the error messages are leading me to believe that 2.7 version in run on 3 code).
Or your local copy is not in right shape.
I tested it on 3.4 and cpython default and everything was OK.
[localhost 3.4]$ ./python.exe -m unittest -v Lib/test/test_urllib2net.py
...
Ran 15 tests in 36.672s
OK
[localhost 3.4]$ hg log -r 3.4
changeset: 92551:bce1594023f9
branch: 3.4
parent: 92548:381d6362c7bc
parent: 92546:ff2cb4dc36e7
user: Serhiy Storchaka <storchaka@gmail.com>
date: Tue Sep 23 23:23:41 2014 +0300
description:
Merge heads
[localhost cpython]$ ./python.exe -m unittest -v Lib/test/test_urllib2net.py
...
Ran 15 tests in 32.779s
OK
[localhost cpython]$ hg log -r tip
changeset: 92555:064f6baeb6bd
tag: tip
user: Georg Brandl <georg@python.org>
date: Wed Sep 24 09:08:12 2014 +0200
files: Python/importlib.h
description:
Update importlib.h frozen bytecode (changed due to commit c0ca9d32aed4).

The buildbots are not showing this error too. I suggest you reset your local copy with the pristine one from remote, do a make distclean; ./configure; make and then run the tests.