Pin dnspython < 2 for now; fully fixing it is going to be a bit involved.

docs/changes/1661.bugfix

 Fix compatibility with dnspython 2.
+
+.. caution:: This currently means that it can be imported. But it
+             cannot yet be used. gevent has a pinned dependency on
+             dnspython < 2 for now.

setup.py

@@ -291,7 +291,7 @@ del _to_cythonize
 ## Extras
 
 EXTRA_DNSPYTHON = [
-    'dnspython >= 1.16.0',
+    'dnspython >= 1.16.0, < 2.0',
     'idna',
 ]
 EXTRA_EVENTS = [

src/gevent/resolver/dnspython.py

@@ -112,7 +112,7 @@ def _patch_dns():
     def extra_all(mod_name):
         return extras.get(mod_name, ())
 
-    def after_import_hook(dns):
+    def after_import_hook(dns): # pylint;disable=redefined-outer-name
         # Runs while still in the original patching scope.
         # The dns.rdata:get_rdata_class() function tries to
         # dynamically import modules using __import__ and then walk
@@ -150,7 +150,6 @@ def _patch_dns():
 
     top.rdata.__import__ = _no_dynamic_imports
 
-
     return top
 
 dns = _patch_dns()