fix #521 copy of dict to prevent it updates (#523)

* fix #521 copy of dict to prevent it updates

* some PEP8 and typo fixes

pydal/adapters/base.py

@@ -180,7 +180,7 @@ def expand_all(self, fields, tabledict):
         return new_fields
 
     def parse_value(self, value, field_itype, field_type, blob_decode=True):
-        #[Note - gi0baro] I think next if block can be (should be?) avoided
+        # [Note - gi0baro] I think next if block can be (should be?) avoided
         if field_type != 'blob' and isinstance(value, str):
             try:
                 value = value.decode(self.db._db_codec)
@@ -309,7 +309,7 @@ def parse(self, rows, fields, colnames, blob_decode=True, cacheable=False):
         # Old style virtual fields
         for tablename, tmp in fields_virtual.items():
             table = tmp[0]
-            ### old style virtual fields
+            # ## old style virtual fields
             for item in table.virtualfields:
                 try:
                     rowsobj = rowsobj.setvirtualfields(**{tablename: item})
@@ -322,7 +322,7 @@ def iterparse(self, sql, fields, colnames, blob_decode=True,
                   cacheable=False):
         """
         Iterator to parse one row at a time.
-        It doen't support the old style virtual fields
+        It doesn't support the old style virtual fields
         """
         return IterRows(self.db, sql, fields, colnames, blob_decode, cacheable)
 
@@ -359,7 +359,7 @@ def before_execute(self, command):
 
 class SQLAdapter(BaseAdapter):
     commit_on_alter_table = False
-    #[Note - gi0baro] can_select_for_update should be deprecated and removed
+    # [Note - gi0baro] can_select_for_update should be deprecated and removed
     can_select_for_update = True
     execution_handlers = []
     migrator_cls = Migrator
@@ -615,14 +615,14 @@ def _select_wcols(self, query, fields, left=False, join=False,
                 ijoin_tables, ijoin_on, itables_to_merge, ijoin_on_tables,
                 iimportant_tablenames, iexcluded, itablemap
             ) = self._build_joins_for_select(tablemap, join)
-            tablemap = merge_tablemaps(tablemap, itables_to_merge)
+            tablemap = merge_tablemaps(tablemap, dict(**itables_to_merge))
             tablemap = merge_tablemaps(tablemap, itablemap)
         if left:
             (
                 join_tables, join_on, tables_to_merge, join_on_tables,
                 important_tablenames, excluded, jtablemap
             ) = self._build_joins_for_select(tablemap, left)
-            tablemap = merge_tablemaps(tablemap, tables_to_merge)
+            tablemap = merge_tablemaps(tablemap, dict(**tables_to_merge))
             tablemap = merge_tablemaps(tablemap, jtablemap)
         current_scope = outer_scoped + list(tablemap)
         query_env = dict(current_scope=current_scope,