Fix accessing Python reserved word attributes on js objects (#3926)

Removes some of the compatibility break introduced in #3617.
Update faq too.

docs/project/changelog.md

@@ -53,6 +53,11 @@ myst:
   `{env: {HOME: whatever_directory}}`.
   {pr}`3870`
 
+- {{ Fix }} `getattr(jsproxy, 'python_reserved_word')` works as expected again
+  (as well as `hasattr` and `setattr`). This fixes a regression introduced in
+  {pr}`3617`.
+  {pr}`3926`
+
 ### Packages
 
 - OpenBLAS has been added and scipy now uses OpenBLAS rather than CLAPACK

docs/usage/faq.md

@@ -441,30 +441,70 @@ lambda = (x) => {return x + 1};
 pyodide.runPython(`from js import lambda; print(lambda(1))`);
 ```
 
-For JS objects with attributes that are Python reserved keywords, {py:func}`getattr` and {py:func}`setattr` can be used to access the attribute by name:
+If you try to access a Python reserved word followed by one or more underscores
+on a `JsProxy`, Pyodide will remove a single underscore:
+
+```pyodide
+pyodide.runPython(`
+    from js import Array
+    print(Array.from_([1,2,3]))
+`);
+```
+
+If you meant to access the keyword with an underscore at the end, you'll have to
+add an extra one:
+
+```pyodide
+globalThis.lambda = 7;
+globalThis.lambda_ = 8;
+pyodide.runPython(`
+    from js import lambda_, lambda__
+    print(lambda_, lambda__) # 7, 8
+`);
+```
+
+Another example:
+
+```pyodide
+people = {global: "lots and lots"};
+pyodide.runPython(`
+    from js import people
+    # the dir contains global_ but not global:
+    assert "global_" in dir(people)
+    assert "global" not in dir(people)
+    people.global_ = 'even more'
+    print(people.global_)
+`);
+```
+
+You can also use `getattr`, `setattr`, and `delattr` to access the attribute:
 
 ```pyodide
 pyodide.runPython(`
     from js import Array
     fromFunc = getattr(Array, 'from')
     print(fromFunc([1,2,3]))
-    `);
+`);
 
 people = {global: "lots and lots"};
 pyodide.runPython(`
     from js import people
     setattr(people, 'global', 'even more')
     print(getattr(people, 'global'))
-    `);
+`);
 ```
 
-For objects whose names are keywords, one can similarly use {py:func}`getattr` on the `js` module itself:
+For JavaScript globals whose names are keywords, one can similarly use
+{py:func}`getattr` on the `js` module itself:
 
 ```pyodide
-lambda = (x) => {return x + 1};
+globalThis.lambda = 7;
+globalThis.lambda_ = 8;
 pyodide.runPython(`
     import js
     js_lambda = getattr(js, 'lambda')
-    print(js_lambda(1))
-    `);
+    js_lambda_ = getattr(js, 'lambda_')
+    js_lambda__ = getattr(js, 'lambda__')
+    print(js_lambda, js_lambda_, js_lambda__) # 7, 7, 8
+`);
 ```

src/core/hiwire.c

@@ -947,7 +947,7 @@ EM_JS(bool, isReservedWord, (int word), {
  * action: a javascript string, one of get, set, or delete. For error reporting.
  * word: a javascript string, the property being accessed
  */
-EM_JS(int, normalizeReservedWords, (int action, int word), {
+EM_JS(int, normalizeReservedWords, (int word), {
   // clang-format off
   // 1. if word is not a reserved word followed by 0 or more underscores, return
   //    it unchanged.
@@ -960,19 +960,14 @@ EM_JS(int, normalizeReservedWords, (int action, int word), {
   if (noTrailing_ !== word) {
     return word.slice(0, -1);
   }
-  // 3. If the word is exactly a reserved word, this is an error.
-  let action_ptr = stringToNewUTF8(action);
-  let word_ptr = stringToNewUTF8(word);
-  _setReservedError(action_ptr, word_ptr);
-  _free(action_ptr);
-  _free(word_ptr);
-  throw new Module._PropagatePythonError();
+  // 3. If the word is exactly a reserved word, return it unchanged
+  return word;
   // clang-format on
 });
 
 EM_JS_REF(JsRef, JsObject_GetString, (JsRef idobj, const char* ptrkey), {
   let jsobj = Hiwire.get_value(idobj);
-  let jskey = normalizeReservedWords("get", UTF8ToString(ptrkey));
+  let jskey = normalizeReservedWords(UTF8ToString(ptrkey));
   if (jskey in jsobj) {
     return Hiwire.new_value(jsobj[jskey]);
   }
@@ -985,7 +980,7 @@ JsObject_SetString,
 (JsRef idobj, const char* ptrkey, JsRef idval),
 {
   let jsobj = Hiwire.get_value(idobj);
-  let jskey = normalizeReservedWords("set", UTF8ToString(ptrkey));
+  let jskey = normalizeReservedWords(UTF8ToString(ptrkey));
   let jsval = Hiwire.get_value(idval);
   jsobj[jskey] = jsval;
 });
@@ -993,7 +988,7 @@ JsObject_SetString,
 
 EM_JS_NUM(errcode, JsObject_DeleteString, (JsRef idobj, const char* ptrkey), {
   let jsobj = Hiwire.get_value(idobj);
-  let jskey = normalizeReservedWords("delete", UTF8ToString(ptrkey));
+  let jskey = normalizeReservedWords(UTF8ToString(ptrkey));
   delete jsobj[jskey];
 });
 

src/tests/test_jsproxy.py

@@ -2409,12 +2409,15 @@ def test_python_reserved_keywords(selenium):
     assert o.async___ == 3
     assert getattr(o, "async_") == 1  # noqa: B009
     assert getattr(o, "async__") == 2  # noqa: B009
-    with pytest.raises(AttributeError, match="async"):
-        getattr(o, "async")
-    with pytest.raises(AttributeError, match="reserved.*set.*'async_'"):
-        setattr(o, "async", 2)
-    with pytest.raises(AttributeError, match="reserved.*delete.*'async_'"):
-        delattr(o, "async")
+    assert getattr(o, "async") == 1
+
+    assert hasattr(o, "async_")
+    assert hasattr(o, "async")
+    setattr(o, "async", 2)
+    assert o.async_ == 2
+    delattr(o, "async")
+    assert not hasattr(o, "async_")
+    assert not hasattr(o, "async")
 
 
 @run_in_pyodide