repair pg8000 and pin to 1.16.6 min version

Due to tlocke/pg8000@3a2e743
we no longer decode the description.  pin to 1.16.6 as minimum version
so that we don't need to track version changes in code.

Change-Id: I192c851eb2337f37467560a3cbb87f7235884788

lib/sqlalchemy/dialects/postgresql/pg8000.py

@@ -12,7 +12,7 @@
     :url: https://pypi.org/project/pg8000/
 
 .. versionchanged:: 1.4  The pg8000 dialect has been updated for version
-   1.16.5 and higher, and is again part of SQLAlchemy's continuous integration
+   1.16.6 and higher, and is again part of SQLAlchemy's continuous integration
    with full feature support.
 
 .. _pg8000_unicode:
@@ -119,21 +119,15 @@ def bind_processor(self, dialect):
 
 class _PGJSON(JSON):
     def result_processor(self, dialect, coltype):
-        if dialect._dbapi_version > (1, 10, 1):
-            return None  # Has native JSON
-        else:
-            return super(_PGJSON, self).result_processor(dialect, coltype)
+        return None
 
     def get_dbapi_type(self, dbapi):
         return dbapi.JSON
 
 
 class _PGJSONB(JSONB):
     def result_processor(self, dialect, coltype):
-        if dialect._dbapi_version > (1, 10, 1):
-            return None  # Has native JSON
-        else:
-            return super(_PGJSON, self).result_processor(dialect, coltype)
+        return None
 
     def get_dbapi_type(self, dbapi):
         return dbapi.JSONB
@@ -240,8 +234,7 @@ def pre_exec(self):
         if not self.compiled:
             return
 
-        if self.dialect._dbapi_version > (1, 16, 0):
-            self.set_input_sizes()
+        self.set_input_sizes()
 
 
 class PGCompiler_pg8000(PGCompiler):
@@ -271,7 +264,11 @@ class PGDialect_pg8000(PGDialect):
     execution_ctx_cls = PGExecutionContext_pg8000
     statement_compiler = PGCompiler_pg8000
     preparer = PGIdentifierPreparer_pg8000
-    description_encoding = "use_encoding"
+
+    # reversed as of pg8000 1.16.6.  1.16.5 and lower
+    # are no longer compatible
+    description_encoding = None
+    # description_encoding = "use_encoding"
 
     colspecs = util.update_copy(
         PGDialect.colspecs,
@@ -302,9 +299,8 @@ def __init__(self, client_encoding=None, **kwargs):
         PGDialect.__init__(self, **kwargs)
         self.client_encoding = client_encoding
 
-    def initialize(self, connection):
-        self.supports_sane_multi_rowcount = self._dbapi_version >= (1, 9, 14)
-        super(PGDialect_pg8000, self).initialize(connection)
+        if self._dbapi_version < (1, 16, 6):
+            raise NotImplementedError("pg8000 1.16.6 or greater is required")
 
     @util.memoized_property
     def _dbapi_version(self):
@@ -452,7 +448,7 @@ def on_connect(conn):
 
             fns.append(on_connect)
 
-        if self._dbapi_version > (1, 16, 0) and self._json_deserializer:
+        if self._json_deserializer:
 
             def on_connect(conn):
                 # json

setup.cfg

@@ -58,7 +58,7 @@ oracle =
     cx_oracle>=7,<8;python_version<"3"
     cx_oracle>=7;python_version>="3"
 postgresql = psycopg2>=2.7
-postgresql_pg8000 = pg8000
+postgresql_pg8000 = pg8000>=1.16.6
 postgresql_asyncpg =
     asyncpg;python_version>="3"
     greenlet