rfc7508.py test failure (macOS with py27, py34-310)

[nieder]

On macOS 10.14.6, I'm getting a test failure on rfc7508.py (from v0.2.8):

running test
Traceback (most recent call last):
  File "/sw/build.build/pyasn1-modules-py310-0.2.8-1/pyasn1-modules-0.2.8/setup.py", line 137, in <module>
    setup(**params)
  File "/sw/lib/python3.10/site-packages/setuptools/__init__.py", line 153, in setup
    return distutils.core.setup(**attrs)
  File "/sw/lib/python3.10/distutils/core.py", line 148, in setup
    dist.run_commands()
  File "/sw/lib/python3.10/distutils/dist.py", line 966, in run_commands
    self.run_command(cmd)
  File "/sw/lib/python3.10/distutils/dist.py", line 985, in run_command
    cmd_obj.run()
  File "/sw/build.build/pyasn1-modules-py310-0.2.8-1/pyasn1-modules-0.2.8/setup.py", line 126, in run
    suite = unittest.TestLoader().loadTestsFromNames(
  File "/sw/lib/python3.10/unittest/loader.py", line 220, in loadTestsFromNames
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/sw/lib/python3.10/unittest/loader.py", line 220, in <listcomp>
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/sw/lib/python3.10/unittest/loader.py", line 154, in loadTestsFromName
    module = __import__(module_name)
  File "/sw/build.build/pyasn1-modules-py310-0.2.8-1/pyasn1-modules-0.2.8/tests/__main__.py", line 13, in <module>
    suite = unittest.TestLoader().loadTestsFromNames(
  File "/sw/lib/python3.10/unittest/loader.py", line 220, in loadTestsFromNames
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/sw/lib/python3.10/unittest/loader.py", line 220, in <listcomp>
    suites = [self.loadTestsFromName(name, module) for name in names]
  File "/sw/lib/python3.10/unittest/loader.py", line 154, in loadTestsFromName
    module = __import__(module_name)
  File "/sw/build.build/pyasn1-modules-py310-0.2.8-1/pyasn1-modules-0.2.8/tests/test_rfc7508.py", line 18, in <module>
    from pyasn1_modules import rfc7508
  File "/sw/build.build/pyasn1-modules-py310-0.2.8-1/pyasn1-modules-0.2.8/pyasn1_modules/rfc7508.py", line 44, in <module>
    class HeaderFieldName(char.VisibleString):
  File "/sw/build.build/pyasn1-modules-py310-0.2.8-1/pyasn1-modules-0.2.8/pyasn1_modules/rfc7508.py", line 46, in HeaderFieldName
    constraint.PermittedAlphabetConstraint(*string.printable) -
TypeError: unsupported operand type(s) for -: 'PermittedAlphabetConstraint' and 'PermittedAlphabetConstraint'

This happens with all python versions I've tested, including python3.10.2. There was no issue building v0.2.7.