Add JsProxy.to_py method

src/core/js2python.c

@@ -9,9 +9,6 @@
 #include "jsproxy.h"
 #include "pyproxy.h"
 
-// Since we're going *to* Python, just let any Python exceptions at conversion
-// bubble out to Python
-
 PyObject*
 _js2python_allocate_string(int size, int max_code_point)
 {
@@ -67,15 +64,27 @@ _js2python_memoryview(JsRef id)
   return PyMemoryView_FromObject(jsproxy);
 }
 
-PyObject*
-_js2python_jsproxy(JsRef id)
-{
-  return JsProxy_create(id);
-}
+EM_JS_REF(PyObject*, js2python, (JsRef id), {
+  let value = Module.hiwire.get_value(id);
+  let result = Module.__js2python_convertImmutable(value);
+  // clang-format off
+  if (result !== 0) {
+    return result;
+  }
+  if (value['byteLength'] !== undefined) {
+    return __js2python_memoryview(id);
+  } else {
+    return _JsProxy_create(id);
+  }
+  // clang-format on
+})
+
+EM_JS_REF(PyObject*, js2python_convert, (JsRef id, int depth), {
+  return Module.__js2python_convert(id, new Map(), depth);
+});
 
-// TODO: Add some meaningful order
-EM_JS_REF(PyObject*, __js2python, (JsRef id), {
-  function __js2python_string(value)
+EM_JS_NUM(errcode, js2python_init, (), {
+  Module.__js2python_string = function(value)
   {
     // The general idea here is to allocate a Python string and then
     // have Javascript write directly into its buffer.  We first need
@@ -124,39 +133,174 @@ EM_JS_REF(PyObject*, __js2python, (JsRef id), {
     }
 
     return result;
-  }
+  };
 
-  // clang-format off
-  let value = Module.hiwire.get_value(id);
-  let type = typeof value;
-  if (type === 'string') {
-    return __js2python_string(value);
-  } else if (type === 'number') {
-    return __js2python_number(value);
-  } else if (value === undefined || value === null) {
-    return __js2python_none();
-  } else if (value === true) {
-    return __js2python_true();
-  } else if (value === false) {
-    return __js2python_false();
-  } else if (Module.PyProxy.isPyProxy(value)) {
-    return __js2python_pyproxy(Module.PyProxy._getPtr(value));
-  } else if (value['byteLength'] !== undefined) {
-    return __js2python_memoryview(id);
-  } else {
-    return __js2python_jsproxy(id);
-  }
-  // clang-format on
-});
+  Module.__js2python_convertImmutable = function(value)
+  {
+    let type = typeof value;
+    // clang-format off
+    if (type === 'string') {
+      return Module.__js2python_string(value);
+    } else if (type === 'number') {
+      return __js2python_number(value);
+    } else if (value === undefined || value === null) {
+      return __js2python_none();
+    } else if (value === true) {
+      return __js2python_true();
+    } else if (value === false) {
+      return __js2python_false();
+    } else if (Module.PyProxy.isPyProxy(value)) {
+      return __js2python_pyproxy(Module.PyProxy._getPtr(value));
+    }
+    // clang-format on
+    return 0;
+  };
 
-PyObject*
-js2python(JsRef id)
-{
-  return (PyObject*)__js2python(id);
-}
+  Module.__js2python_convertList = function(obj, map, depth)
+  {
+    let list = _PyList_New(obj.length);
+    // clang-format off
+    if (list === 0) {
+      // clang-format on
+      return 0;
+    }
+    map.set(obj, list);
+    for (let i = 0; i < obj.length; i++) {
+      let entryid = Module.hiwire.new_value(obj[i]);
+      let item = Module.__js2python_convert(entryid, map, depth);
+      Module.hiwire.decref(entryid);
+      // clang-format off
+      if (item === 0) {
+        // clang-format on
+        _Py_DecRef(list);
+        return 0;
+      }
+      // PyList_SetItem steals a reference to item no matter what
+      let errcode = _PyList_SetItem(list, i, item);
+      // clang-format off
+      if (errcode === -1) {
+        // clang-format on
+        _Py_DecRef(list);
+        return 0;
+      }
+    }
+    return list;
+  };
+
+  Module.__js2python_convertMap = function(obj, entries, map, depth)
+  {
+    let dict = _PyDict_New();
+    // clang-format off
+    if (dict === 0) {
+      // clang-format on
+      return 0;
+    }
+    map.set(obj, dict);
+    for (let[key_js, value_js] of entries) {
+      let key_id = Module.hiwire.new_value(key_js);
+      let key_py = Module.__js2python_convert(key_id, map, depth);
+      Module.hiwire.decref(key_id);
+      // clang-format off
+      if (key_py === 0) {
+        // clang-format on
+        _Py_DecRef(dict);
+        return 0;
+      }
+
+      let value_id = Module.hiwire.new_value(value_js);
+      let value_py = Module.__js2python_convert(value_id, map, depth);
+      Module.hiwire.decref(value_id);
+      // clang-format off
+      if (value_py === 0) {
+        // clang-format on
+        _Py_DecRef(dict);
+        return 0;
+      }
+
+      // PyDict_SetItem does not steal references
+      let errcode = _PyDict_SetItem(dict, key_py, value_py);
+      _Py_DecRef(key_py);
+      _Py_DecRef(value_py);
+      // clang-format off
+      if (errcode === -1) {
+        // clang-format on
+        _Py_DecRef(dict);
+        return 0;
+      }
+    }
+    return dict;
+  };
+
+  Module.__js2python_convertSet = function(obj, map, depth)
+  {
+    let set = _PySet_New(0);
+    // clang-format off
+    if (set === 0) {
+      // clang-format on
+      return 0;
+    }
+    map.set(obj, set);
+    for (let key_js of obj) {
+      let key_id = Module.hiwire.new_value(key_js);
+      let key_py = Module.__js2python_convert(key_id, map, depth);
+      Module.hiwire.decref(key_id);
+      // clang-format off
+      if (key_py === 0) {
+        // clang-format on
+        _Py_DecRef(set);
+        return 0;
+      }
+      let errcode = _PySet_Add(set, key_py);
+      _Py_DecRef(key_py);
+      // clang-format off
+      if (errcode === -1) {
+        // clang-format on
+        _Py_DecRef(set);
+        return 0;
+      }
+    }
+    return set;
+  };
+
+  Module.__js2python_convertOther = function(id, value, map, depth)
+  {
+    let toStringTag = Object.prototype.toString.call(value);
+    // clang-format off
+    if (Array.isArray(value) || value === "[object HTMLCollection]" ||
+                                           value === "[object NodeList]") {
+      return Module.__js2python_convertList(value, map, depth);
+    }
+    if (toStringTag === "[object Map]" || value instanceof Map) {
+      return Module.__js2python_convertMap(value, value.entries(), map, depth);
+    }
+    if (toStringTag === "[object Set]" || value instanceof Set) {
+      return Module.__js2python_convertSet(value, map, depth);
+    }
+    if (toStringTag === "[object Object]" && (value.constructor === undefined || value.constructor.name === "Object")) {
+      return Module.__js2python_convertMap(value, Object.entries(value), map, depth);
+    }
+    // clang-format on
+    return _JsProxy_create(id);
+  };
+
+  Module.__js2python_convert = function(id, map, depth)
+  {
+    let value = Module.hiwire.get_value(id);
+    let result = Module.__js2python_convertImmutable(value);
+    // clang-format off
+    if (result !== 0) {
+      return result;
+    }
+    if (depth === 0) {
+      return _JsProxy_create(id);
+    }
+    result = map.get(value);
+    if (result !== undefined) {
+      return result;
+    }
+    // clang-format on
+    return Module.__js2python_convertOther(id, value, map, depth - 1);
+  };
 
-int
-js2python_init()
-{
   return 0;
-}
+})

src/core/js2python.h

@@ -17,6 +17,9 @@
 PyObject*
 js2python(JsRef x);
 
+PyObject*
+js2python_convert(JsRef x, int depth);
+
 /** Initialize any global variables used by this module. */
 int
 js2python_init();

src/core/jsproxy.c

@@ -306,6 +306,25 @@ JsProxy_Dir(PyObject* self, PyObject* _args)
   return result;
 }
 
+static PyObject*
+JsProxy_toPy(PyObject* self, PyObject* const* args, Py_ssize_t nargs)
+{
+  if (nargs > 1) {
+    PyErr_Format(
+      PyExc_TypeError, "to_py expected at most 1 argument, got %zd", nargs);
+    return NULL;
+  }
+  int depth = -1;
+  if (nargs == 1) {
+    int overflow;
+    depth = PyLong_AsLongAndOverflow(args[0], &overflow);
+    if (overflow == 0 && depth == -1 && PyErr_Occurred()) {
+      return NULL;
+    }
+  }
+  return js2python_convert(GET_JSREF(self), depth);
+}
+
 static int
 JsProxy_Bool(PyObject* o)
 {
@@ -382,7 +401,12 @@ static PyMethodDef JsProxy_Methods[] = {
   { "__dir__",
     (PyCFunction)JsProxy_Dir,
     METH_NOARGS,
-    "Returns a list of the members and methods on the object." },
+    PyDoc_STR("Returns a list of the members and methods on the object.") },
+  {
+    "to_py",
+    (PyCFunction)JsProxy_toPy,
+    METH_FASTCALL,
+    PyDoc_STR("Convert the JsProxy to a native Python object (as best as possible)")},
   { NULL }
 };
 // clang-format on

src/tests/test_typeconversions.py

@@ -441,6 +441,69 @@ def test_python2js_with_depth(selenium):
     )
 
 
+def test_to_py(selenium):
+    result = selenium.run_js(
+        """
+        window.a = new Map([[1, [1,2,new Set([1,2,3])]], [2, new Map([[1,2],[2,7]])]]);
+        a.get(2).set("a", a);
+        let result = [];
+        for(let i = 0; i < 4; i++){
+            result.push(pyodide.runPython(`
+                from js import a
+                repr(a.to_py(${i}))
+            `));
+        }
+        return result;
+        """
+    )
+    assert result == [
+        "[object Map]",
+        "{1: 1,2,[object Set], 2: [object Map]}",
+        "{1: [1, 2, [object Set]], 2: {1: 2, 2: 7, 'a': [object Map]}}",
+        "{1: [1, 2, {1, 2, 3}], 2: {1: 2, 2: 7, 'a': {...}}}",
+    ]
+
+    result = selenium.run_js(
+        """
+        window.a = { "x" : 2, "y" : 7, "z" : [1,2] };
+        a.z.push(a);
+        let result = [];
+        for(let i = 0; i < 4; i++){
+            result.push(pyodide.runPython(`
+                from js import a
+                repr(a.to_py(${i}))
+            `));
+        }
+        return result;
+        """
+    )
+    assert result == [
+        "[object Object]",
+        "{'x': 2, 'y': 7, 'z': 1,2,[object Object]}",
+        "{'x': 2, 'y': 7, 'z': [1, 2, [object Object]]}",
+        "{'x': 2, 'y': 7, 'z': [1, 2, {...}]}",
+    ]
+
+    result = selenium.run_js(
+        """
+        class Temp {
+            constructor(){
+                this.x = 2;
+                this.y = 7;
+            }
+        }
+        window.a = new Temp();
+        let result = pyodide.runPython(`
+            from js import a
+            b = a.to_py()
+            repr(type(b))
+        `);
+        return result;
+        """
+    )
+    assert result == "<class 'JsProxy'>"
+
+
 @pytest.mark.xfail
 def test_py2js_set(selenium):
     selenium.run("a = {1, 2, 3}")