feat: python error formatting (freeCodeCamp#54185)

Co-authored-by: Naomi <nhcarrigan@gmail.com>

e2e/editor.spec.ts

@@ -1,30 +1,65 @@
-import { expect, test } from '@playwright/test';
+import { expect, test, type Page } from '@playwright/test';
 
-test.beforeEach(async ({ page }) => {
-  await page.goto(
-    '/learn/2022/responsive-web-design/learn-html-by-building-a-cat-photo-app/step-3'
-  );
-});
+async function focusEditor({
+  page,
+  isMobile,
+  browserName
+}: {
+  page: Page;
+  isMobile: boolean;
+  browserName: string;
+}) {
+  const monacoEditor = page.getByLabel('Editor content');
+
+  // The editor has an overlay div, which prevents the click event from bubbling up in iOS Safari.
+  // This is a quirk in this browser-OS combination, and the workaround here is to use `.focus()`
+  // in place of `.click()` to focus on the editor.
+  // Ref: https://www.quirksmode.org/blog/archives/2014/02/mouse_event_bub.html
+  if (isMobile && browserName === 'webkit') {
+    await monacoEditor.focus();
+  } else {
+    await monacoEditor.click();
+  }
+}
 
 test.describe('Editor Component', () => {
   test('should allow the user to insert text', async ({
     page,
     isMobile,
     browserName
   }) => {
-    const monacoEditor = page.getByLabel('Editor content');
+    await page.goto(
+      '/learn/2022/responsive-web-design/learn-html-by-building-a-cat-photo-app/step-3'
+    );
 
-    // The editor has an overlay div, which prevents the click event from bubbling up in iOS Safari.
-    // This is a quirk in this browser-OS combination, and the workaround here is to use `.focus()`
-    // in place of `.click()` to focus on the editor.
-    // Ref: https://www.quirksmode.org/blog/archives/2014/02/mouse_event_bub.html
-    if (isMobile && browserName === 'webkit') {
-      await monacoEditor.focus();
-    } else {
-      await monacoEditor.click();
-    }
+    await focusEditor({ page, isMobile, browserName });
     await page.keyboard.insertText('<h2>FreeCodeCamp</h2>');
     const text = page.getByText('<h2>FreeCodeCamp</h2>');
     await expect(text).toBeVisible();
   });
 });
+
+test.describe('Python Terminal', () => {
+  test('should display error message when the user enters invalid code', async ({
+    page,
+    isMobile,
+    browserName
+  }) => {
+    await page.goto(
+      'learn/scientific-computing-with-python/learn-string-manipulation-by-building-a-cipher/step-2'
+    );
+
+    await focusEditor({ page, isMobile, browserName });
+    // First clear the editor
+    await page.keyboard.press('Control+a');
+    await page.keyboard.press('Backspace');
+    // Then enter invalid code
+    await page.keyboard.insertText('def');
+    const preview = page.getByTestId('preview-pane');
+
+    // While it's displayed on multiple lines, the string itself has no newlines, hence:
+    const error = `>>> Traceback (most recent call last):  File "main.py", line 1    def       ^SyntaxError: invalid syntax`;
+    // It shouldn't take this long, but the Python worker can be slow to respond.
+    await expect(preview).toContainText(error, { timeout: 15000 });
+  });
+});

tools/client-plugins/browser-scripts/python-worker.ts

@@ -3,6 +3,7 @@
 import { loadPyodide, type PyodideInterface } from 'pyodide/pyodide.js';
 import pkg from 'pyodide/package.json';
 import type { PyProxy, PythonError } from 'pyodide/ffi';
+import * as helpers from '@freecodecamp/curriculum-helpers';
 
 const ctx: Worker & typeof globalThis = self as unknown as Worker &
   typeof globalThis;
@@ -53,6 +54,15 @@ async function setupPyodide() {
   // pyodide modifies self while loading.
   Object.freeze(self);
 
+  // eslint-disable-next-line @typescript-eslint/no-unsafe-call, @typescript-eslint/no-unsafe-member-access
+  pyodide.FS.writeFile(
+    '/home/pyodide/ast_helpers.py',
+    helpers.python.astHelpers,
+    {
+      encoding: 'utf8'
+    }
+  );
+
   ignoreRunMessages = true;
   postMessage({ type: 'stopped' });
 }
@@ -134,10 +144,19 @@ function initRunPython() {
     else:
       return ""
   `);
+  runPython(`
+def print_exception():
+    from ast_helpers import format_exception
+    formatted = format_exception(exception=sys.last_value, traceback=sys.last_traceback, filename="<exec>", new_filename="main.py")
+    print(formatted)
+`);
+  // eslint-disable-next-line @typescript-eslint/no-unsafe-call
+  const printException = globals.get('print_exception') as PyProxy &
+    (() => string);
 
   // eslint-disable-next-line @typescript-eslint/no-unsafe-call
   const getResetId = globals.get('__get_reset_id') as PyProxy & (() => string);
-  return { runPython, getResetId, globals };
+  return { runPython, getResetId, globals, printException };
 }
 
 ctx.onmessage = (e: PythonRunEvent | ListenRequestEvent | CancelEvent) => {
@@ -166,13 +185,16 @@ function handleRunRequest(data: PythonRunEvent['data']) {
   // TODO: use reset-terminal for clarity?
   postMessage({ type: 'reset' });
 
-  const { runPython, getResetId, globals } = initRunPython();
+  const { runPython, getResetId, globals, printException } = initRunPython();
   // use pyodide.runPythonAsync if we want top-level await
   try {
     runPython(code);
   } catch (e) {
     const err = e as PythonError;
-    console.error(e);
+    // the formatted exception is printed to the terminal
+    printException();
+    // but the full error is logged to the console for debugging
+    console.error(err);
     const resetId = getResetId();
     // TODO: if a user raises a KeyboardInterrupt with a custom message this
     // will be treated as a reset, the client will resend their code and this
@@ -187,6 +209,7 @@ function handleRunRequest(data: PythonRunEvent['data']) {
     }
   } finally {
     getResetId.destroy();
+    printException.destroy();
     globals.destroy();
   }
 }