Keyword only arguments for transform()

Also renamed columns= to types=

Closes #165

docs/python-api.rst

@@ -926,12 +926,12 @@ The ``table.transform()`` method can do all of these things, by implementing a m
 
 The ``.transform()`` method takes a number of parameters, all of which are optional.
 
-To alter the type of a column, use the first argument:
+To alter the type of a column, use the ``types=`` argument:
 
 .. code-block:: python
 
     # Convert the 'age' column to an integer, and 'weight' to a float
-    table.transform({"age": int, "weight": float})
+    table.transform(types={"age": int, "weight": float})
 
 The ``rename=`` parameter can rename columns:
 

sqlite_utils/db.py

@@ -718,7 +718,8 @@ class Table(Queryable):
 
     def transform(
         self,
-        columns=None,
+        *,
+        types=None,
         rename=None,
         drop=None,
         pk=DEFAULT,
@@ -728,7 +729,7 @@ class Table(Queryable):
     ):
         assert self.exists(), "Cannot transform a table that doesn't exist yet"
         sqls = self.transform_sql(
-            columns=columns,
+            types=types,
             rename=rename,
             drop=None,
             pk=pk,
@@ -754,7 +755,8 @@ class Table(Queryable):
 
     def transform_sql(
         self,
-        columns=None,
+        *,
+        types=None,
         rename=None,
         drop=None,
         pk=DEFAULT,
@@ -763,7 +765,7 @@ class Table(Queryable):
         drop_foreign_keys=None,
         tmp_suffix=None,
     ):
-        columns = columns or {}
+        types = types or {}
         rename = rename or {}
         drop = drop or set()
         new_table_name = "{}_new_{}".format(
@@ -773,7 +775,7 @@ class Table(Queryable):
         new_column_pairs = []
         copy_from_to = {column: column for column, _ in current_column_pairs}
         for name, type_ in current_column_pairs:
-            type_ = columns.get(name) or type_
+            type_ = types.get(name) or type_
             if name in drop:
                 del [copy_from_to[name]]
                 continue

tests/test_transform.py

@@ -18,7 +18,7 @@ import pytest
         ),
         # Change column type
         (
-            {"columns": {"age": int}},
+            {"types": {"age": int}},
             [
                 "CREATE TABLE [dogs_new_suffix] (\n   [id] INTEGER PRIMARY KEY,\n   [name] TEXT,\n   [age] INTEGER\n);",
                 "INSERT INTO [dogs_new_suffix] ([id], [name], [age]) SELECT [id], [name], [age] FROM [dogs]",
@@ -48,7 +48,7 @@ import pytest
         ),
         # Convert type AND rename column
         (
-            {"columns": {"age": int}, "rename": {"age": "dog_age"}},
+            {"types": {"age": int}, "rename": {"age": "dog_age"}},
             [
                 "CREATE TABLE [dogs_new_suffix] (\n   [id] INTEGER PRIMARY KEY,\n   [name] TEXT,\n   [dog_age] INTEGER\n);",
                 "INSERT INTO [dogs_new_suffix] ([id], [name], [dog_age]) SELECT [id], [name], [age] FROM [dogs]",