feat(python): show custom message if syntax error (#53040)

client/i18n/locales/english/translations.json

@@ -373,6 +373,7 @@
     "running-tests": "// running tests",
     "tests-completed": "// tests completed",
     "console-output": "// console output",
+    "syntax-error": "Your code raised a error before we could run any tests. Please fix it and try again.",
     "sign-in-save": "Sign in to save your progress",
     "download-solution": "Download my solution",
     "download-results": "Download my results",

client/src/templates/Challenges/redux/execute-challenge-saga.js

@@ -209,7 +209,7 @@ function* executeTests(testRunner, tests, testTimeout = 5000) {
         throw err;
       }
     } catch (err) {
-      const { actual, expected } = err;
+      const { actual, expected, syntaxError } = err;
 
       newTest.message = text
         .replace('--fcc-expected--', expected)
@@ -217,6 +217,9 @@ function* executeTests(testRunner, tests, testTimeout = 5000) {
       if (err === 'timeout') {
         newTest.err = 'Test timed out';
         newTest.message = `${newTest.message} (${newTest.err})`;
+      } else if (syntaxError) {
+        newTest.err = 'syntax error';
+        newTest.message = `<p>${i18next.t('learn.syntax-error')}</p>`;
       } else {
         const { message, stack } = err;
         newTest.err = message + '\n' + stack;

tools/client-plugins/browser-scripts/python-test-evaluator.ts

@@ -133,7 +133,20 @@ input = __inputGen(${JSON.stringify(input ?? [])})
 
     // Evaluates the learner's code so that any variables they define are
     // available to the test.
-    runPython(code);
+    try {
+      runPython(code);
+    } catch (err) {
+      // We don't, yet, want user code to raise exceptions. When they do, we
+      // count this as a failing test.
+      ctx.postMessage({
+        err: {
+          message: (err as Error).message,
+          stack: (err as Error).stack,
+          syntaxError: true
+        }
+      });
+      return;
+    }
     // TODO: remove the next line, creating __locals, once all the tests access
     // variables directly.
     runPython('__locals = globals()');