Improved code compilation pattern, closes #472

Author: simonw

docs/cli.rst

@@ -1359,12 +1359,9 @@ The following example adds a new ``score`` column, then updates it to list a ran
     random.seed(10)
 
     def convert(value):
-        global random
         return random.random()
     '
 
-Note the ``global random`` line here. Due to the way the tool compiles Python code, this is necessary to ensure the ``random`` module is available within the ``convert()`` function. If you were to omit this you would see a ``NameError: name 'random' is not defined`` error.
-
 .. _cli_convert_recipes:
 
 sqlite-utils convert recipes

sqlite_utils/utils.py

@@ -432,12 +432,11 @@ def progressbar(*args, **kwargs):
 
 
 def _compile_code(code, imports, variable="value"):
-    locals = {}
     globals = {"r": recipes, "recipes": recipes}
     # If user defined a convert() function, return that
     try:
-        exec(code, globals, locals)
-        return locals["convert"]
+        exec(code, globals)
+        return globals["convert"]
     except (AttributeError, SyntaxError, NameError, KeyError, TypeError):
         pass
 
@@ -464,8 +463,8 @@ def _compile_code(code, imports, variable="value"):
 
     for import_ in imports:
         globals[import_.split(".")[0]] = __import__(import_)
-    exec(code_o, globals, locals)
-    return locals["fn"]
+    exec(code_o, globals)
+    return globals["fn"]
 
 
 def chunks(sequence: Iterable, size: int) -> Iterable[Iterable]:

tests/test_cli_convert.py

@@ -606,3 +606,23 @@ def test_convert_hyphen_workaround(fresh_db_and_path):
     assert list(db["names"].rows) == [
         {"id": 1, "name": "-"},
     ]
+
+
+def test_convert_initialization_pattern(fresh_db_and_path):
+    db, db_path = fresh_db_and_path
+    db["names"].insert_all([{"id": 1, "name": "Cleo"}], pk="id")
+    result = CliRunner().invoke(
+        cli.cli,
+        [
+            "convert",
+            db_path,
+            "names",
+            "name",
+            "-",
+        ],
+        input="import random\nrandom.seed(1)\ndef convert(value):    return random.randint(0, 100)",
+    )
+    assert 0 == result.exit_code, result.output
+    assert list(db["names"].rows) == [
+        {"id": 1, "name": "17"},
+    ]