On Travis, I've seen what seems to be flaky test failures during the download of Python modules before, never locally. I'm not sure that the test name is meaningful here but including the most recent one for completeness. integration_tests.plugins.test_python_plugin.PythonPluginTestCase.test_build_doesnt_get_bad_install_directory_lp1586546 Downloading 'PyYAML-3.11.tar.gz' 23% Traceback (most recent call last): File "/usr/lib/python3.5/runpy.py", line 184, in _run_module_as_main "__main__", mod_spec) File "/usr/lib/python3.5/runpy.py", line 85, in _run_code exec(code, run_globals) File "/usr/lib/python3.5/unittest/__main__.py", line 18, in <module> main(module=None) File "/usr/lib/python3.5/unittest/main.py", line 94, in __init__ self.runTests() File "/usr/lib/python3.5/unittest/main.py", line 255, in runTests self.result = testRunner.run(self.test) File "/usr/lib/python3.5/unittest/runner.py", line 183, in run result.printErrors() File "/usr/lib/python3.5/unittest/runner.py", line 109, in printErrors self.printErrorList('ERROR', self.errors) File "/usr/lib/python3.5/unittest/runner.py", line 117, in printErrorList self.stream.writeln("%s" % err) File "/usr/lib/python3.5/unittest/runner.py", line 25, in writeln self.write(arg) BlockingIOError: [Errno 11] write could not complete without blocking