make migrate.changeset.databases PEP-8 clean and add it to the API docs

1 files changed, 23 insertions, 9 deletions

diff --git a/migrate/changeset/databases/visitor.py b/migrate/changeset/databases/visitor.py
index 437dc68..60216cc 100644
--- a/migrate/changeset/databases/visitor.py
+++ b/migrate/changeset/databases/visitor.py
@@ -1,20 +1,34 @@
+"""
+   Module for visitor class mapping.
+"""
 import sqlalchemy as sa
-from migrate.changeset.databases import sqlite,postgres,mysql,oracle
+from migrate.changeset.databases import sqlite, postgres, mysql, oracle
 from migrate.changeset import ansisql
 
 # Map SA dialects to the corresponding Migrate extensions
 dialects = {
-    sa.engine.default.DefaultDialect : ansisql.ANSIDialect,
-    sa.databases.sqlite.SQLiteDialect : sqlite.SQLiteDialect,
-    sa.databases.postgres.PGDialect : postgres.PGDialect,
-    sa.databases.mysql.MySQLDialect : mysql.MySQLDialect,
-    sa.databases.oracle.OracleDialect : oracle.OracleDialect,
+    sa.engine.default.DefaultDialect: ansisql.ANSIDialect,
+    sa.databases.sqlite.SQLiteDialect: sqlite.SQLiteDialect,
+    sa.databases.postgres.PGDialect: postgres.PGDialect,
+    sa.databases.mysql.MySQLDialect: mysql.MySQLDialect,
+    sa.databases.oracle.OracleDialect: oracle.OracleDialect,
 }
 
-def get_engine_visitor(engine,name):
-    return get_dialect_visitor(engine.dialect,name)
 
-def get_dialect_visitor(sa_dialect,name):
+def get_engine_visitor(engine, name):
+    """
+    Get the visitor implementation for the given database engine.
+    """
+    return get_dialect_visitor(engine.dialect, name)
+
+
+def get_dialect_visitor(sa_dialect, name):
+    """
+    Get the visitor implementation for the given dialect.
+
+    Finds the visitor implementation based on the dialect class and
+    returns and instance initialized with the given name.
+    """
     sa_dialect_cls = sa_dialect.__class__
     migrate_dialect_cls = dialects[sa_dialect_cls]
     return migrate_dialect_cls.visitor(name)