[Python-Dev] regrtest.py mystery

[Tim Peters]

We do this after running every test:

        # Unload the newly imported modules (best effort finalization)
        for module in sys.modules.keys():
            if module not in save_modules and module.startswith("test."):
                test_support.unload(module)

Unfortunately, that doesn't nuke whatever damaged non-test module objects
may have been left behind.  If I change it to make a truly <wink> best
effort:

            if module not in save_modules:
                test_support.unload(module)

then about a dozen std tests fail in mysterious ways, but only when running
more than one test.  Like just running

    test_email test_string

causes test_string to die like so:

python ../lib/test/regrtest.py -v test_email test_string

...

test test_string crashed -- exceptions.AttributeError: 'NoneType' object
                            has no attribute 'get'
Traceback (most recent call last):
  File "../lib/test/regrtest.py", line 305, in runtest
    the_module = __import__(test, globals(), locals(), [])
  File "../lib/test\test_string.py", line 34, in ?
    string_tests.run_method_tests(test)
  File "../lib/test\string_tests.py", line 233, in run_method_tests
    verify('hello world'.encode('zlib') == data)
  File "C:\CODE\PYTHON\lib\encodings\__init__.py", line 43, in
search_function
    entry = _cache.get(encoding,_unknown)
AttributeError: 'NoneType' object has no attribute 'get'

It seems generally the case that these failures are due to various
module-level names getting rebound to None.  A simpler example:

python  ../lib/test/regrtest.py -v test_string test_string

...

test test_string crashed -- exceptions.AttributeError: 'NoneType' object
                            has no attribute 'compress'
Traceback (most recent call last):
  File "../lib/test/regrtest.py", line 305, in runtest
    the_module = __import__(test, globals(), locals(), [])
  File "../lib/test\test_string.py", line 34, in ?
    string_tests.run_method_tests(test)
  File "../lib/test\string_tests.py", line 233, in run_method_tests
    verify('hello world'.encode('zlib') == data)
  File "C:\CODE\PYTHON\lib\encodings\zlib_codec.py", line 25, in zlib_encode
    output = zlib.compress(input)
AttributeError: 'NoneType' object has no attribute 'compress'

What's up with that?  So far, they all seem to involve the encodings
directory ...