test_http_body_pipe() of test_urllib2 uses a subprocess, no idea if it's related:

        cmd = [sys.executable, "-c", r"pass"]
        for headers in {}, {"Content-Length": 30}:
            with subprocess.Popen(cmd, stdout=subprocess.PIPE) as proc:
                req = Request("http://example.com/", proc.stdout, headers)
                ...

See also my issue #29915 "Drop Mac OS X Tiger support in Python 3.7?" :-)

http://buildbot.python.org/all/builders/x86%20Tiger%203.x/builds/597/steps/test/logs/stdio

./python.exe -E -c 'import sys ; from sysconfig import get_platform ; print("%s-%d.%d" % (get_platform(), *sys.version_info[:2]))' >platform
/bin/sh: line 1: pybuildbot.identify: command not found
./python.exe  ./Tools/scripts/run_tests.py -j 1 -u all -W --slowest --timeout=900 -j2
make: [buildbottest] Error 127 (ignored)
== CPython 3.7.0a0 (heads/master:5d7a8d0, May 1 2017, 12:22:06) [GCC 4.0.1 (Apple Computer, Inc. build 5367)]
==   Darwin-8.11.1-i386-32bit little-endian
==   hash algorithm: siphash24 32bit
==  cwd: /Users/db3l/buildarea/3.x.bolen-tiger/build/build/test_python_12700
==  encodings: locale=UTF-8, FS=utf-8
Testing with flags: sys.flags(debug=0, inspect=0, interactive=0, optimize=0, dont_write_bytecode=0, no_user_site=0, no_site=0, ignore_environment=1, verbose=0, bytes_warning=2, quiet=0, hash_randomization=1, isolated=0)
Using random seed 2778758
Run tests in parallel using 2 child processes
0:00:12 [  1/405] test_deque passed
0:00:35 [  2/405] test_trace passed (34 sec)
0:00:56 [  3/405] test_capi passed -- running: test_socket (44 sec)
0:00:57 [  4/405] test_pkgimport passed -- running: test_socket (45 sec)
0:01:02 [  5/405] test_socket passed (49 sec)
0:01:07 [  6/405] test_imaplib passed
0:01:18 [  7/405] test_urllib2 passed
Fatal Python error: Py_Initialize: can't initialize sys standard streams
OSError: [Errno 9] Bad file descriptor

Current thread 0xa000d000 (most recent call first):
Fatal Python error: Py_Initialize: can't initialize sys standard streams
OSError: [Errno 9] Bad file descriptor

Current thread 0xa000d000 (most recent call first):
0:01:20 [  8/405] test_getargs2 passed
0:01:24 [  9/405] test_calendar passed
0:01:25 [ 10/405] test_unpack_ex passed