Add docstrings and typing to db_engine_specs and sql_parse (#8058)

* Add typing to db_engine_specs

* Add more type annotations and docstrings

* Add docstrings and typing to sql_parse and db_engine_specs

* Refine select_star

* Fix execute and add more docstrings

* Revert kwargs change from execute

* Remove redundant or

* Align view and table getter schema types

* Fix return type of latest_partition

* Remove some typing from presto

* Improve docstring for __extract_from_token

superset/db_engine_specs/sqlite.py

@@ -15,8 +15,11 @@
 # specific language governing permissions and limitations
 # under the License.
 # pylint: disable=C,R,W
+from datetime import datetime
 from typing import List
 
+from sqlalchemy.engine.reflection import Inspector
+
 from superset.db_engine_specs.base import BaseEngineSpec
 from superset.utils import core as utils
 
@@ -38,7 +41,7 @@ class SqliteEngineSpec(BaseEngineSpec):
     }
 
     @classmethod
-    def epoch_to_dttm(cls):
+    def epoch_to_dttm(cls) -> str:
         return "datetime({col}, 'unixepoch')"
 
     @classmethod
@@ -69,13 +72,13 @@ class SqliteEngineSpec(BaseEngineSpec):
             raise Exception(f"Unsupported datasource_type: {datasource_type}")
 
     @classmethod
-    def convert_dttm(cls, target_type, dttm):
+    def convert_dttm(cls, target_type: str, dttm: datetime) -> str:
         iso = dttm.isoformat().replace("T", " ")
         if "." not in iso:
             iso += ".000000"
         return "'{}'".format(iso)
 
     @classmethod
-    def get_table_names(cls, inspector, schema):
+    def get_table_names(cls, inspector: Inspector, schema: str) -> List[str]:
         """Need to disregard the schema for Sqlite"""
         return sorted(inspector.get_table_names())