Address style issues and some downstream failures

asdf/schema.py

@@ -11,7 +11,7 @@
 import numpy as np
 import yaml
 from jsonschema import validators as mvalidators
-from jsonschema.exceptions import ValidationError, RefResolutionError
+from jsonschema.exceptions import RefResolutionError, ValidationError
 
 from . import constants, extension, generic_io, reference, tagged, treeutil, util, versioning, yamlutil
 from .config import get_config
@@ -261,7 +261,7 @@ def _create_validator(validators=YAML_VALIDATORS, visit_repeat_nodes=False):
 
     @attr.s
     class ASDFValidator(base_cls):
-        _context = attr.ib(factory = lambda: _ValidationContext())
+        _context = attr.ib(factory=lambda: _ValidationContext())
         ctx = attr.ib(default=None)
         serialization_context = attr.ib(default=None)
 

setup.cfg

@@ -35,6 +35,10 @@ install_requires =
     semantic_version>=2.8
     asdf-standard>=1.0.1
     asdf-transform-schemas>=0.2.2
+    # Multiple downstream packages accidentally depend on asdf to
+    # install six.  As a friendly gesture we list six as a dependency
+    # for older Python versions.
+    six;python_version<"3.8"
 
 [options.extras_require]
 all =

tox.ini

@@ -18,7 +18,7 @@ deps=
     legacy: gwcs==0.9.1
     legacy: semantic_version==2.8
     legacy: pyyaml==3.13
-    legacy: jsonschema==3.0.2
+    legacy: jsonschema==4.0.1
     legacy: numpy~=1.14.6
     legacy: pytest~=4.6.11
     legacy: astropy~=3.0.0