Add REPL-style bare expression evaluation support with tests

Implements `_add_repl_print` helper to wrap bare expressions for REPL-style output in `demo` and `io_test` modes. Updates evaluation pipeline, adds unit tests, and expands Postman collection for REPL-specific cases.

Author: m-messer

evaluation_function/evaluation.py

@@ -1,3 +1,4 @@
+import ast
 import json
 import os
 import shutil
@@ -76,6 +77,21 @@ def addSuccess(self, test):
 """
 
 
+def _add_repl_print(code: str) -> str:
+    """Wrap last bare expression in print(repr(...)) for REPL-style output."""
+    try:
+        tree = ast.parse(code)
+    except SyntaxError:
+        return code
+    if not tree.body or not isinstance(tree.body[-1], ast.Expr):
+        return code
+    node = tree.body[-1].value
+    if (isinstance(node, ast.Call) and
+            isinstance(node.func, ast.Name) and node.func.id == 'print'):
+        return code
+    return code + f"\nprint(repr({ast.unparse(node)}))"
+
+
 def _run_code(code: str, stdin: str) -> tuple[str, str, bool, list[Image.Image]]:
     plot_dir = tempfile.mkdtemp()
     preamble = _PREAMBLE_TEMPLATE.format(plot_dir=plot_dir)
@@ -122,6 +138,7 @@ def _upload_plots(images: list[Image.Image]) -> list[str]:
 
 
 def _evaluate_demo(response: str, result: Result) -> Result:
+    response = _add_repl_print(response)
     stdout, stderr, timed_out, images = _run_code(response, "")
     if timed_out:
         result.add_feedback("error", f"Code timed out after {_TIMEOUT}s.")
@@ -136,6 +153,7 @@ def _evaluate_demo(response: str, result: Result) -> Result:
 
 def _evaluate_io(response: str, tests: list, result: Result) -> Result:
     passed = 0
+    response = _add_repl_print(response)
 
     for i, test in enumerate(tests, 1):
         inject = test.get("inject")

evaluation_function/evaluation_test.py

@@ -109,6 +109,28 @@ def test_inject_string_value(self):
         self.assertTrue(result["is_correct"])
 
 
+class TestReplExpression(unittest.TestCase):
+
+    def test_bare_expression_demo(self):
+        result = evaluation_function("3.14159*2*5", None, {"mode": "demo"}).to_dict()
+        self.assertIn("31.4159", result["feedback"])
+
+    def test_bare_expression_io_test(self):
+        params = _params(_test("", "31.4159\n"))
+        result = evaluation_function("3.14159*2*5", None, params).to_dict()
+        self.assertTrue(result["is_correct"])
+
+    def test_existing_print_not_double_wrapped(self):
+        params = _params(_test("", "31.4159\n"))
+        result = evaluation_function("print(31.4159)", None, params).to_dict()
+        self.assertTrue(result["is_correct"])
+
+    def test_assignment_no_auto_print(self):
+        params = _params(_test("", "5\n"))
+        result = evaluation_function("x = 5", None, params).to_dict()
+        self.assertFalse(result["is_correct"])
+
+
 _PLOT_CODE = "import matplotlib.pyplot as plt\nplt.plot([1, 2, 3])\n"
 _MULTI_PLOT_CODE = (
     "import matplotlib.pyplot as plt\n"

postman/evaluatePython.postman_collection.json

@@ -785,6 +785,88 @@
             }
           ]
         },
+        {
+          "name": "26 – REPL expression in demo mode",
+          "request": {
+            "method": "POST",
+            "header": [
+              { "key": "Content-Type", "value": "application/json" }
+            ],
+            "body": {
+              "mode": "raw",
+              "raw": "{\n  \"response\": \"3.14159*2*5\",\n  \"answer\": \"\",\n  \"params\": {\n    \"mode\": \"demo\"\n  }\n}",
+              "options": { "raw": { "language": "json" } }
+            },
+            "url": { "raw": "{{baseUrl}}", "host": ["{{baseUrl}}"] }
+          },
+          "event": [
+            {
+              "listen": "prerequest",
+              "script": {
+                "type": "text/javascript",
+                "exec": ["pm.request.timeout = 40000;"]
+              }
+            },
+            {
+              "listen": "test",
+              "script": {
+                "type": "text/javascript",
+                "exec": [
+                  "pm.test('Status 200', () => {",
+                  "    pm.expect(pm.response.code, 'Body: ' + pm.response.text()).to.equal(200);",
+                  "});",
+                  "",
+                  "pm.test('Bare expression output is auto-displayed (REPL style)', () => {",
+                  "    pm.expect(pm.response.json().result.feedback).to.include('31.4159');",
+                  "});"
+                ]
+              }
+            }
+          ]
+        },
+        {
+          "name": "27 – REPL expression in io_test mode",
+          "request": {
+            "method": "POST",
+            "header": [
+              { "key": "Content-Type", "value": "application/json" }
+            ],
+            "body": {
+              "mode": "raw",
+              "raw": "{\n  \"response\": \"3.14159*2*5\",\n  \"answer\": \"\",\n  \"params\": {\n    \"mode\": \"io_test\",\n    \"tests\": [\n      { \"input\": \"\", \"expected_output\": \"31.4159\\n\", \"hidden\": false }\n    ]\n  }\n}",
+              "options": { "raw": { "language": "json" } }
+            },
+            "url": { "raw": "{{baseUrl}}", "host": ["{{baseUrl}}"] }
+          },
+          "event": [
+            {
+              "listen": "prerequest",
+              "script": {
+                "type": "text/javascript",
+                "exec": ["pm.request.timeout = 40000;"]
+              }
+            },
+            {
+              "listen": "test",
+              "script": {
+                "type": "text/javascript",
+                "exec": [
+                  "pm.test('Status 200', () => {",
+                  "    pm.expect(pm.response.code, 'Body: ' + pm.response.text()).to.equal(200);",
+                  "});",
+                  "",
+                  "pm.test('is_correct is true', () => {",
+                  "    pm.expect(pm.response.json().result.is_correct).to.be.true;",
+                  "});",
+                  "",
+                  "pm.test('Feedback reports 1/1 tests passed', () => {",
+                  "    pm.expect(pm.response.json().result.feedback).to.include('1/1 tests passed');",
+                  "});"
+                ]
+              }
+            }
+          ]
+        },
         {
           "name": "20 – Image generation (demo mode)",
           "request": {