Py_GetVersion() (in Python/getversion.c) builds the version string returned by sys.version:

PyOS_snprintf(version, sizeof(version), "%.80s (%.80s) %.80s",
PY_VERSION, Py_GetBuildInfo(), Py_GetCompiler());

In turn, Py_GetBuildInfo() (in Modules/getbuildinfo.c) returns the "build" portion of Python's version string. When available, the tag returned by "hg id -t" constitutes part of that build string.

The problem is that when using mqueue the result of "hg id -t" can be pretty long. For example:

bpo-21226-fix-PyImport_ExecCodeModuleObject.diff qbase qtip tip

That's 74 characters for just part of a build string that may be well over 100 characters. However, Py_GetVersion() truncates it to 80 characters.

The consequence is that this value of sys.version causes platform._sys_version() to fail since the version string does not match the expected pattern.

So either Py_GetVersion() should relax (-1) or Py_GetBuildInfo() should restrict the length of the resulting build string (+1). Would it work to truncate just the hgid part so that the whole string returned by Py_GetBuildInfo() is no more than length 80? E.g.

-    PyOS_snprintf(buildinfo, sizeof(buildinfo),
-                  "%s%s%s, %.20s, %.9s", hgid, sep, revision, DATE, TIME);
+    PyOS_snprintf(buildinfo, 80,
+                  "%.43s%.1s%.13s, %.20s, %.9s", hgid, sep, revision, DATE, TIME);

Any comments on the proposal to restrict the length of the returned string from Py_GetBuildInfo() to 80 characters?

Currently Py_GetBuildInfo() just returns a long untruncated string. Perhaps it would be safer to leave that as it is, and just make the parsing in the “platform” module more tolerant. What do you think?

I never really cared about the details in Py_GetBuildInfo(), but it would be nice if the test suite would run :)

>>> Py_GetBuildInfo = pythonapi.Py_GetBuildInfo
>>> Py_GetBuildInfo.restype = c_char_p
>>> Py_GetBuildInfo()  # Not truncated
'qbase qtip subprocess-stderr_redirect_with_no_stdout_redirect-2.diff tip:0b641285389d+, May 13 2016, 02:10:26'

Demo of my problem with the test suite:

$ ./python -m test.regrtest
Traceback (most recent call last):
  [. . .]
  File "/media/disk/home/proj/python/cpython/Lib/test/test_support.py", line 1423, in check_impl_detail
    return guards.get(platform.python_implementation().lower(), default)
  File "/media/disk/home/proj/python/cpython/Lib/platform.py", line 1451, in python_implementation
    return _sys_version()[0]
  File "/media/disk/home/proj/python/cpython/Lib/platform.py", line 1416, in _sys_version
    repr(sys_version))
ValueError: failed to parse CPython sys.version: '2.7.11+ (qbase qtip subprocess-stderr_redirect_with_no_stdout_redirect-2.diff tip:0b64128) \n[GCC 5.3.0]'

New changeset b86e259271b3 by Martin Panter in branch '2.7':
Issue bpo-21313: Tolerate truncated buildinfo in sys.version
https://hg.python.org/cpython/rev/b86e259271b3

New changeset 4deec876db0d by Martin Panter in branch '3.5':
Issue bpo-21313: Tolerate truncated buildinfo in sys.version
https://hg.python.org/cpython/rev/4deec876db0d

New changeset aec5a3fc4890 by Martin Panter in branch 'default':
Issue bpo-21313: Merge version parsing from 3.5
https://hg.python.org/cpython/rev/aec5a3fc4890

Closing now that platform._sys_version() can tolerate the truncated version info.