Respect formatting in ast.FormattedValue for local_python_executor (#660)

Co-authored-by: Ilya Amelchenkov <ilya@fstr.app>
Co-authored-by: Albert Villanova del Moral <8515462+albertvillanova@users.noreply.github.com>

src/smolagents/local_python_executor.py

@@ -1229,8 +1229,14 @@ def evaluate_ast(
         # For loop -> execute the loop
         return evaluate_for(expression, *common_params)
     elif isinstance(expression, ast.FormattedValue):
-        # Formatted value (part of f-string) -> evaluate the content and return
-        return evaluate_ast(expression.value, *common_params)
+        # Formatted value (part of f-string) -> evaluate the content and format it
+        value = evaluate_ast(expression.value, *common_params)
+        # Early return if no format spec
+        if not expression.format_spec:
+            return value
+        # Apply format specification
+        format_spec = evaluate_ast(expression.format_spec, *common_params)
+        return format(value, format_spec)
     elif isinstance(expression, ast.If):
         # If -> execute the right branch
         return evaluate_if(expression, *common_params)

tests/test_local_python_executor.py

@@ -122,6 +122,22 @@ class PythonInterpreterTester(unittest.TestCase):
         assert result == "This is x: 3."
         self.assertDictEqualNoPrint(state, {"x": 3, "text": "This is x: 3.", "_operations_count": 6})
 
+    def test_evaluate_f_string_with_format(self):
+        code = "text = f'This is x: {x:.2f}.'"
+        state = {"x": 3.336}
+        result, _ = evaluate_python_code(code, {}, state=state)
+        assert result == "This is x: 3.34."
+        self.assertDictEqualNoPrint(state, {"x": 3.336, "text": "This is x: 3.34.", "_operations_count": 8})
+
+    def test_evaluate_f_string_with_complex_format(self):
+        code = "text = f'This is x: {x:>{width}.{precision}f}.'"
+        state = {"x": 3.336, "width": 10, "precision": 2}
+        result, _ = evaluate_python_code(code, {}, state=state)
+        assert result == "This is x:       3.34."
+        self.assertDictEqualNoPrint(
+            state, {"x": 3.336, "width": 10, "precision": 2, "text": "This is x:       3.34.", "_operations_count": 14}
+        )
+
     def test_evaluate_if(self):
         code = "if x <= 3:\n    y = 2\nelse:\n    y = 5"
         state = {"x": 3}