Sync to internal Google development.

4 files changed, 810 insertions, 0 deletions

diff --git a/upb/bindings/python/setup.py b/upb/bindings/python/setup.py
new file mode 100644
index 0000000..8abaff8
--- /dev/null
+++ b/upb/bindings/python/setup.py
@@ -0,0 +1,14 @@
+from distutils.core import setup, Extension
+
+setup(name='upb',
+      version='0.1',
+      ext_modules=[
+          Extension('upb.__init__', ['upb.c'],
+              include_dirs=['../../'],
+              define_macros=[("UPB_UNALIGNED_READS_OK", 1)],
+              library_dirs=['../../upb'],
+              libraries=['upb_pic'],
+          ),
+      ],
+      packages=['upb']
+      )
diff --git a/upb/bindings/python/test.py b/upb/bindings/python/test.py
new file mode 100644
index 0000000..29a6c45
--- /dev/null
+++ b/upb/bindings/python/test.py
@@ -0,0 +1,72 @@
+
+import upb
+import unittest
+
+class TestFieldDef(unittest.TestCase):
+  def test_construction(self):
+    fielddef1 = upb.FieldDef()
+    self.assertTrue(fielddef1.number is None)
+    self.assertTrue(fielddef1.name is None)
+    self.assertTrue(fielddef1.type is None)
+    self.assertEqual(fielddef1.label, upb.LABEL_OPTIONAL)
+
+    fielddef2 = upb.FieldDef(number=5, name="field2",
+                             label=upb.LABEL_REQUIRED, type=upb.TYPE_INT32,
+                             type_name="MyType")
+
+    self.assertTrue(id(fielddef1) != id(fielddef2))
+    self.assertEqual(fielddef2.number, 5)
+    self.assertEqual(fielddef2.name, "field2")
+    self.assertEqual(fielddef2.label, upb.LABEL_REQUIRED)
+    self.assertEqual(fielddef2.type, upb.TYPE_INT32)
+    self.assertEqual(fielddef2.type_name, "MyType")
+
+    fielddef2.number = 8
+    self.assertEqual(fielddef2.number, 8)
+
+    fielddef2.name = "xxx"
+    self.assertEqual(fielddef2.name, "xxx")
+
+    fielddef2.label = upb.LABEL_REPEATED
+    self.assertEqual(fielddef2.label, upb.LABEL_REPEATED)
+
+    fielddef2.type = upb.TYPE_FLOAT
+    self.assertEqual(fielddef2.type, upb.TYPE_FLOAT)
+
+  def test_nosubclasses(self):
+    def create_subclass():
+      class MyClass(upb.FieldDef):
+        pass
+
+    self.assertRaises(TypeError, create_subclass)
+
+  # TODO: test that assigning invalid values is properly prevented.
+
+class TestMessageDef(unittest.TestCase):
+  def test_construction(self):
+    msgdef1 = upb.MessageDef()
+    self.assertTrue(msgdef1.fqname is None)
+    self.assertEqual(msgdef1.fields(), [])
+
+    fields = [upb.FieldDef(number=1, name="field1", type=upb.TYPE_INT32)]
+    msgdef2 = upb.MessageDef(fqname="Message2", fields=fields)
+
+    self.assertEqual(set(msgdef2.fields()), set(fields))
+
+    f2 = upb.FieldDef(number=2, name="field2", type=upb.TYPE_INT64)
+    msgdef2.add_field(f2)
+
+    fields.append(f2)
+    self.assertEqual(set(msgdef2.fields()), set(fields))
+
+class TestSymbolTable(unittest.TestCase):
+  def test_construction(self):
+    s = upb.SymbolTable()
+    self.assertEqual(s.defs(), []);
+
+    s.add_def(upb.MessageDef(fqname="A"))
+    self.assertTrue(s.lookup("A") is not None)
+    self.assertTrue(s.lookup("A") is s.lookup("A"))
+
+if __name__ == '__main__':
+  unittest.main()
diff --git a/upb/bindings/python/upb.c b/upb/bindings/python/upb.c
new file mode 100644
index 0000000..497074b
--- /dev/null
+++ b/upb/bindings/python/upb.c
@@ -0,0 +1,724 @@
+/*
+ * upb - a minimalist implementation of protocol buffers.
+ *
+ * Copyright (c) 2009 Google Inc.  See LICENSE for details.
+ * Author: Josh Haberman <jhaberman@gmail.com>
+ *
+ * Python extension exposing the core of upb: definitions, handlers,
+ * and a message type.
+ */
+
+#include <stddef.h>
+#include <Python.h>
+#include "upb/def.h"
+#include "upb/msg.h"
+
+static bool streql(const char *a, const char *b) { return strcmp(a, b) == 0; }
+
+PyObject *PyUpb_Error(const char *str) {
+  PyErr_SetString(PyExc_TypeError, str);
+  return NULL;
+}
+
+int PyUpb_ErrorInt(const char *str) {
+  PyErr_SetString(PyExc_TypeError, str);
+  return -1;
+}
+
+#define PyUpb_CheckStatus(status) \
+  if (!upb_ok(status)) return PyUpb_Error((status)->str);
+
+static upb_accessor_vtbl *PyUpb_AccessorForField(upb_fielddef *f);
+
+
+/* Object cache ***************************************************************/
+
+// For objects that are just wrappers around a C object pointer, we keep a
+// cache mapping C pointer -> wrapper object.  This allows us to consistently
+// vend the same Python object given the same C object.  This prevents us from
+// creating too many Python objects unnecessarily.  Just as importantly, it
+// provides the expected semantics:
+//
+//   if field.subdef is field.subdef:
+//     print "Sanity prevails."
+//
+// If we conjured up a new wrapper object every time, the above would not be
+// true.
+//
+// The cost is having to put all such objects in a table, but since this only
+// applies to schema-level objects (defs, handlers, etc) this seems acceptable.
+// We do *not* have to put all message objects in this table.
+//
+// We use weak refs so that the cache does not prevent the wrapper objects from
+// being collected.  The table is stored as a static variable; to use
+// sub-interpreters this would need to change, but I believe that using
+// sub-interpreters is exceedingly rare in practice.
+
+typedef struct {
+  PyObject_HEAD;
+  void *obj;
+  PyObject *weakreflist;
+} PyUpb_ObjWrapper;
+
+static PyObject *obj_cache = NULL;
+static PyObject *reverse_cache = NULL;
+static PyObject *weakref_callback = NULL;
+
+// Utility functions for manipulating Python dictionaries keyed by pointer.
+
+static PyObject *PyUpb_StringForPointer(const void *ptr) {
+  PyObject *o = PyString_FromStringAndSize((const char *)&ptr, sizeof(void*));
+  assert(o);
+  return o;
+}
+
+static PyObject *PyUpb_ObjCacheDeleteCallback(PyObject *self, PyObject *ref) {
+  // Python very unfortunately clears the weakref before running our callback.
+  // This prevents us from using the weakref to find the C pointer we need to
+  // remove from the cache.  As a result we are forced to keep a second map
+  // mapping weakref->C pointer.
+  PyObject *ptr_str = PyDict_GetItem(reverse_cache, ref);
+  assert(ptr_str);
+  int err = PyDict_DelItem(obj_cache, ptr_str);
+  assert(!err);
+  err = PyDict_DelItem(reverse_cache, ref);
+  assert(!err);
+  return Py_None;
+}
+
+static PyObject *PyUpb_ObjCacheGet(const void *obj, PyTypeObject *type) {
+  PyObject *kv = PyUpb_StringForPointer(obj);
+  PyObject *ref = PyDict_GetItem(obj_cache, kv);
+  PyObject *ret;
+  if (ref) {
+    ret = PyWeakref_GetObject(ref);
+    assert(ret != Py_None);
+    Py_INCREF(ret);
+  } else {
+    PyUpb_ObjWrapper *wrapper = (PyUpb_ObjWrapper*)type->tp_alloc(type, 0);
+    wrapper->obj = (void*)obj;
+    wrapper->weakreflist = NULL;
+    ret = (PyObject*)wrapper;
+    ref = PyWeakref_NewRef(ret, weakref_callback);
+    assert(PyWeakref_GetObject(ref) == ret);
+    assert(ref);
+    PyDict_SetItem(obj_cache, kv, ref);
+    PyDict_SetItem(reverse_cache, ref, kv);
+  }
+  assert(ret);
+  Py_DECREF(kv);
+  return ret;
+}
+
+
+/* PyUpb_Def ******************************************************************/
+
+static PyTypeObject *PyUpb_TypeForDef(const upb_def *def);
+
+static void PyUpb_Def_dealloc(PyObject *obj) {
+  PyUpb_ObjWrapper *wrapper = (void*)obj;
+  upb_def_unref((upb_def*)wrapper->obj);
+  obj->ob_type->tp_free(obj);
+}
+
+PyObject *PyUpb_Def_GetOrCreate(const upb_def *def) {
+  return def ? PyUpb_ObjCacheGet(def, PyUpb_TypeForDef(def)) : Py_None;
+}
+
+// Will need to expand once other kinds of defs are supported.
+#define Check_Def(o, badret) Check_MessageDef(o, badret)
+
+
+/* PyUpb_FieldDef *************************************************************/
+
+static PyTypeObject PyUpb_FieldDefType;
+static int PyUpb_FieldDef_setattro(PyObject *o, PyObject *key, PyObject *val);
+
+#define Check_FieldDef(o, badret) \
+  (void*)(((PyUpb_ObjWrapper*)o)->obj); do { \
+    if(!PyObject_TypeCheck(o, &PyUpb_FieldDefType)) { \
+      PyErr_SetString(PyExc_TypeError, "must be a upb.FieldDef"); \
+      return badret; \
+    } \
+  } while(0)
+
+static PyObject *PyUpb_FieldDef_GetOrCreate(const upb_fielddef *f) {
+  return PyUpb_ObjCacheGet(f, &PyUpb_FieldDefType);
+}
+
+static PyObject *PyUpb_FieldDef_new(PyTypeObject *subtype,
+                                    PyObject *args, PyObject *kwds) {
+  return PyUpb_ObjCacheGet(upb_fielddef_new(), subtype);
+}
+
+static int PyUpb_FieldDef_init(PyObject *self, PyObject *args, PyObject *kwds) {
+  if (!kwds) return 0;
+  PyObject *key, *value;
+  Py_ssize_t pos = 0;
+  while (PyDict_Next(kwds, &pos, &key, &value))
+    PyUpb_FieldDef_setattro(self, key, value);
+  return 0;
+}
+
+static void PyUpb_FieldDef_dealloc(PyObject *obj) {
+  PyUpb_ObjWrapper *wrapper = (void*)obj;
+  if (wrapper->weakreflist) PyObject_ClearWeakRefs(obj);
+  upb_fielddef_unref((upb_fielddef*)wrapper->obj);
+  obj->ob_type->tp_free(obj);
+}
+
+static PyObject *PyUpb_FieldDef_getattro(PyObject *obj, PyObject *attr_name) {
+  upb_fielddef *f = Check_FieldDef(obj, NULL);
+  if (!upb_fielddef_ismutable(f)) {
+    PyErr_SetString(PyExc_TypeError, "fielddef is not mutable.");
+    return NULL;
+  }
+  const char *name = PyString_AsString(attr_name);
+  if (streql(name, "name")) {
+    const char *name = upb_fielddef_name(f);
+    return name == NULL ? Py_None : PyString_FromString(name);
+  } else if (streql(name, "number")) {
+    uint32_t num = upb_fielddef_number(f);
+    return num == 0 ? Py_None : PyInt_FromLong(num);
+  } else if (streql(name, "type")) {
+    uint8_t type = upb_fielddef_type(f);
+    return type == 0 ? Py_None : PyInt_FromLong(type);
+  } else if (streql(name, "label")) {
+    return PyInt_FromLong(upb_fielddef_label(f));
+  } else if (streql(name, "type_name")) {
+    const char *name = upb_fielddef_typename(f);
+    return name == NULL ? Py_None : PyString_FromString(name);
+  } else if (streql(name, "subdef")) {
+    // NYI;
+    return NULL;
+  } else if (streql(name, "msgdef")) {
+    // NYI;
+    return NULL;
+  } else {
+    return PyUpb_Error("Invalid fielddef member.");
+  }
+}
+
+static int PyUpb_FieldDef_setattro(PyObject *o, PyObject *key, PyObject *val) {
+  upb_fielddef *f = Check_FieldDef(o, -1);
+  const char *field = PyString_AsString(key);
+  if (!upb_fielddef_ismutable(f))
+    return PyUpb_ErrorInt("fielddef is not mutable.");
+  if (streql(field, "name")) {
+    const char *name = PyString_AsString(val);
+    if (!name || !upb_fielddef_setname(f, name))
+      return PyUpb_ErrorInt("Invalid name");
+  } else if (streql(field, "number")) {
+    // TODO: should check truncation.  Non-security issue.
+    // Non-int will return -1, which is already invalid as a field number.
+    if (!upb_fielddef_setnumber(f, PyInt_AsLong(val)))
+      return PyUpb_ErrorInt("Invalid number");
+  } else if (streql(field, "type")) {
+    // TODO: should check truncation.  Non-security issue.
+    if (!upb_fielddef_settype(f, PyInt_AsLong(val)))
+      return PyUpb_ErrorInt("Invalid type");
+  } else if (streql(field, "label")) {
+    // TODO: should check truncation.  Non-security issue.
+    if (!upb_fielddef_setlabel(f, PyInt_AsLong(val)))
+      return PyUpb_ErrorInt("Invalid label");
+  } else if (streql(field, "type_name")) {
+    const char *name = PyString_AsString(val);
+    if (!name || !upb_fielddef_settypename(f, name))
+      return PyUpb_ErrorInt("Invalid type_name");
+  } else if (streql(field, "default_value")) {
+    // NYI
+    return -1;
+  } else {
+    return PyUpb_ErrorInt("Invalid fielddef member.");
+  }
+  return 0;
+}
+
+static PyTypeObject PyUpb_FieldDefType = {
+  PyObject_HEAD_INIT(NULL)
+  0,                                      /* ob_size */
+  "upb.FieldDef",                         /* tp_name */
+  sizeof(PyUpb_ObjWrapper),               /* tp_basicsize */
+  0,                                      /* tp_itemsize */
+  &PyUpb_FieldDef_dealloc,                /* tp_dealloc */
+  0,                                      /* tp_print */
+  0,                                      /* tp_getattr */
+  0,                                      /* tp_setattr */
+  0,                                      /* tp_compare */
+  0, /* TODO */                           /* tp_repr */
+  0,                                      /* tp_as_number */
+  0,                                      /* tp_as_sequence */
+  0,                                      /* tp_as_mapping */
+  0,                                      /* tp_hash */
+  0,                                      /* tp_call */
+  0,                                      /* tp_str */
+  &PyUpb_FieldDef_getattro,               /* tp_getattro */
+  &PyUpb_FieldDef_setattro,               /* tp_setattro */
+  0,                                      /* tp_as_buffer */
+  Py_TPFLAGS_DEFAULT,                     /* tp_flags */
+  0,                                      /* tp_doc */
+  0,                                      /* tp_traverse */
+  0,                                      /* tp_clear */
+  0,                                      /* tp_richcompare */
+  offsetof(PyUpb_ObjWrapper, weakreflist),/* tp_weaklistoffset */
+  0,                                      /* tp_iter */
+  0,                                      /* tp_iternext */
+  0,                                      /* tp_methods */
+  0,                                      /* tp_members */
+  0,                                      /* tp_getset */
+  0,                                      /* tp_base */
+  0,                                      /* tp_dict */
+  0,                                      /* tp_descr_get */
+  0,                                      /* tp_descr_set */
+  0,                                      /* tp_dictoffset */
+  &PyUpb_FieldDef_init,                   /* tp_init */
+  0,                                      /* tp_alloc */
+  &PyUpb_FieldDef_new,                    /* tp_new */
+  0,                                      /* tp_free */
+};
+
+
+/* PyUpb_MessageDef ***********************************************************/
+
+static PyTypeObject PyUpb_MessageDefType;
+static int PyUpb_MessageDef_setattro(PyObject *o, PyObject *key, PyObject *val);
+
+#define Check_MessageDef(o, badret) \
+  (void*)(((PyUpb_ObjWrapper*)o)->obj); do { \
+    if(!PyObject_TypeCheck(o, &PyUpb_MessageDefType)) { \
+      PyErr_SetString(PyExc_TypeError, "must be a upb.MessageDef"); \
+      return badret; \
+    } \
+  } while(0)
+
+static PyObject *PyUpb_MessageDef_new(PyTypeObject *subtype,
+                                      PyObject *args, PyObject *kwds) {
+  return PyUpb_ObjCacheGet(upb_msgdef_new(), subtype);
+}
+
+static PyObject *PyUpb_MessageDef_add_fields(PyObject *o, PyObject *args);
+
+static int PyUpb_MessageDef_init(PyObject *self, PyObject *args, PyObject *kwds) {
+  if (!kwds) return 0;
+  PyObject *key, *value;
+  Py_ssize_t pos = 0;
+  while (PyDict_Next(kwds, &pos, &key, &value)) {
+    const char *field = PyString_AsString(key);
+    if (streql(field, "fields")) {
+      PyUpb_MessageDef_add_fields(self, value);
+    } else {
+      PyUpb_MessageDef_setattro(self, key, value);
+    }
+  }
+  return 0;
+}
+
+static PyObject *PyUpb_MessageDef_getattro(PyObject *obj, PyObject *attr_name) {
+  upb_msgdef *m = Check_MessageDef(obj, NULL);
+  const char *name = PyString_AsString(attr_name);
+  if (streql(name, "fqname")) {
+    const char *fqname = upb_def_fqname(UPB_UPCAST(m));
+    return fqname == NULL ? Py_None : PyString_FromString(fqname);
+  }
+  return PyObject_GenericGetAttr(obj, attr_name);
+}
+
+static int PyUpb_MessageDef_setattro(PyObject *o, PyObject *key, PyObject *val) {
+  upb_msgdef *m = Check_MessageDef(o, -1);
+  if (!upb_def_ismutable(UPB_UPCAST(m))) {
+    PyErr_SetString(PyExc_TypeError, "MessageDef is not mutable.");
+    return -1;
+  }
+  const char *name = PyString_AsString(key);
+  if (streql(name, "fqname")) {
+    const char *fqname = PyString_AsString(val);
+    if (!fqname || !upb_def_setfqname(UPB_UPCAST(m), fqname))
+      return PyUpb_ErrorInt("Invalid fqname");
+  } else {
+    return PyUpb_ErrorInt("Invalid MessageDef member.");
+  }
+  return 0;
+}
+
+static PyObject *PyUpb_MessageDef_fields(PyObject *obj, PyObject *args) {
+  upb_msgdef *m = Check_MessageDef(obj, NULL);
+  PyObject *ret = PyList_New(0);
+  upb_msg_iter i;
+  for(i = upb_msg_begin(m); !upb_msg_done(i); i = upb_msg_next(m, i)) {
+    upb_fielddef *f = upb_msg_iter_field(i);
+    PyList_Append(ret, PyUpb_FieldDef_GetOrCreate(f));
+  }
+  return ret;
+}
+
+static PyObject *PyUpb_MessageDef_add_fields(PyObject *o, PyObject *fields) {
+  upb_msgdef *m = Check_MessageDef(o, NULL);
+  if (!PySequence_Check(fields)) return PyUpb_Error("Must be a sequence");
+  Py_ssize_t len = PySequence_Length(fields);
+  if (len > UPB_MAX_FIELDS) return PyUpb_Error("Too many fields.");
+  upb_fielddef *f[len];
+  int i;
+  for (i = 0; i < len; i++) {
+    PyObject *field = PySequence_GetItem(fields, i);
+    f[i] = Check_FieldDef(field, NULL);
+  }
+  upb_msgdef_addfields(m, f, len);
+  return Py_None;
+}
+
+static PyObject *PyUpb_MessageDef_add_field(PyObject *o, PyObject *field) {
+  upb_msgdef *m = Check_MessageDef(o, NULL);
+  upb_fielddef *f = Check_FieldDef(field, NULL);
+  upb_msgdef_addfield(m, f);
+  return Py_None;
+}
+
+static PyMethodDef PyUpb_MessageDef_methods[] = {
+  {"add_field", &PyUpb_MessageDef_add_field, METH_O, "Adds a list of fields."},
+  {"add_fields", &PyUpb_MessageDef_add_fields, METH_O, "Adds a list of fields."},
+  {"fields", &PyUpb_MessageDef_fields, METH_NOARGS, "Returns list of fields."},
+  {NULL, NULL}
+};
+
+static PyTypeObject PyUpb_MessageDefType = {
+  PyObject_HEAD_INIT(NULL)
+  0,                                      /* ob_size */
+  "upb.MessageDef",                       /* tp_name */
+  sizeof(PyUpb_ObjWrapper),               /* tp_basicsize */
+  0,                                      /* tp_itemsize */
+  &PyUpb_Def_dealloc,                     /* tp_dealloc */
+  0,                                      /* tp_print */
+  0,                                      /* tp_getattr */
+  0,                                      /* tp_setattr */
+  0,                                      /* tp_compare */
+  0, /* TODO */                           /* tp_repr */
+  0,                                      /* tp_as_number */
+  0,                                      /* tp_as_sequence */
+  0,                                      /* tp_as_mapping */
+  0,                                      /* tp_hash */
+  0,                                      /* tp_call */
+  0,                                      /* tp_str */
+  &PyUpb_MessageDef_getattro,             /* tp_getattro */
+  &PyUpb_MessageDef_setattro,             /* tp_setattro */
+  0,                                      /* tp_as_buffer */
+  Py_TPFLAGS_DEFAULT,                     /* tp_flags */
+  0,                                      /* tp_doc */
+  0,                                      /* tp_traverse */
+  0,                                      /* tp_clear */
+  0,                                      /* tp_richcompare */
+  offsetof(PyUpb_ObjWrapper, weakreflist),/* tp_weaklistoffset */
+  0,                                      /* tp_iter */
+  0,                                      /* tp_iternext */
+  PyUpb_MessageDef_methods,               /* tp_methods */
+  0,                                      /* tp_members */
+  0,                                      /* tp_getset */
+  0,                                      /* tp_base */
+  0,                                      /* tp_dict */
+  0,                                      /* tp_descr_get */
+  0,                                      /* tp_descr_set */
+  0,                                      /* tp_dictoffset */
+  &PyUpb_MessageDef_init,                 /* tp_init */
+  0,                                      /* tp_alloc */
+  &PyUpb_MessageDef_new,                  /* tp_new */
+  0,                                      /* tp_free */
+};
+
+
+static PyTypeObject *PyUpb_TypeForDef(const upb_def *def) {
+  switch(def->type) {
+    case UPB_DEF_MSG: return &PyUpb_MessageDefType;
+    default: return NULL;
+  }
+}
+
+/* PyUpb_SymbolTable **********************************************************/
+
+static PyTypeObject PyUpb_SymbolTableType;
+
+#define Check_SymbolTable(o, badret) \
+  (void*)(((PyUpb_ObjWrapper*)o)->obj); do { \
+    if(!PyObject_TypeCheck(o, &PyUpb_SymbolTableType)) { \
+      PyErr_SetString(PyExc_TypeError, "must be a upb.MessageDef"); \
+      return badret; \
+    } \
+  } while(0)
+
+static PyObject *PyUpb_SymbolTable_new(PyTypeObject *subtype,
+                                       PyObject *args, PyObject *kwds) {
+  return PyUpb_ObjCacheGet(upb_symtab_new(), subtype);
+}
+
+static int PyUpb_SymbolTable_init(PyObject *self, PyObject *args, PyObject *kwds) {
+  return 0;
+}
+
+static void PyUpb_SymbolTable_dealloc(PyObject *obj) {
+  PyUpb_ObjWrapper *wrapper = (void*)obj;
+  upb_symtab_unref((upb_symtab*)wrapper->obj);
+  obj->ob_type->tp_free(obj);
+}
+
+// narg is a lua table containing a list of defs to add.
+static PyObject *PyUpb_SymbolTable_add_defs(PyObject *o, PyObject *defs) {
+  upb_symtab *s = Check_SymbolTable(o, NULL);
+  if (!PySequence_Check(defs)) return PyUpb_Error("Must be a sequence");
+  Py_ssize_t n = PySequence_Length(defs);
+
+  // Prevent stack overflow.
+  if (n > 2048) return PyUpb_Error("Too many defs");
+  upb_def *cdefs[n];
+
+  int i = 0;
+  for (i = 0; i < n; i++) {
+    PyObject *pydef = PySequence_GetItem(defs, i);
+    upb_def *def = Check_MessageDef(pydef, NULL);
+    cdefs[i++] = def;
+    upb_msgdef *md = upb_dyncast_msgdef(def);
+    if (!md) continue;
+    upb_msg_iter j;
+    for(j = upb_msg_begin(md); !upb_msg_done(j); j = upb_msg_next(md, j)) {
+      upb_fielddef *f = upb_msg_iter_field(j);
+      upb_fielddef_setaccessor(f, PyUpb_AccessorForField(f));
+    }
+    upb_msgdef_layout(md);
+  }
+
+  upb_status status = UPB_STATUS_INIT;
+  upb_symtab_add(s, cdefs, n, &status);
+  PyUpb_CheckStatus(&status);
+  return Py_None;
+}
+
+static PyObject *PyUpb_SymbolTable_add_def(PyObject *o, PyObject *def) {
+  PyObject *defs = PyList_New(1);
+  PyList_SetItem(defs, 0, def);
+  return PyUpb_SymbolTable_add_defs(o, defs);
+}
+
+// TODO: update to allow user to choose type of defs.
+static PyObject *PyUpb_SymbolTable_defs(PyObject *o, PyObject *none) {
+  upb_symtab *s = Check_SymbolTable(o, NULL);
+  int count;
+  const upb_def **defs = upb_symtab_getdefs(s, &count, UPB_DEF_ANY);
+  PyObject *ret = PyList_New(count);
+  int i;
+  for(i = 0; i < count; i++)
+    PyList_SetItem(ret, i, PyUpb_Def_GetOrCreate(defs[i]));
+  return ret;
+}
+
+static PyObject *PyUpb_SymbolTable_lookup(PyObject *o, PyObject *arg) {
+  upb_symtab *s = Check_SymbolTable(o, NULL);
+  const char *name = PyString_AsString(arg);
+  const upb_def *def = upb_symtab_lookup(s, name);
+  return PyUpb_Def_GetOrCreate(def);
+}
+
+static PyMethodDef PyUpb_SymbolTable_methods[] = {
+  {"add_def", &PyUpb_SymbolTable_add_def, METH_O, NULL},
+  {"add_defs", &PyUpb_SymbolTable_add_defs, METH_O, NULL},
+  {"defs", &PyUpb_SymbolTable_defs, METH_NOARGS, NULL},
+  {"lookup", &PyUpb_SymbolTable_lookup, METH_O, NULL},
+  {NULL, NULL}
+};
+
+static PyTypeObject PyUpb_SymbolTableType = {
+  PyObject_HEAD_INIT(NULL)
+  0,                                      /* ob_size */
+  "upb.SymbolTable",                      /* tp_name */
+  sizeof(PyUpb_ObjWrapper),               /* tp_basicsize */
+  0,                                      /* tp_itemsize */
+  &PyUpb_SymbolTable_dealloc,             /* tp_dealloc */
+  0,                                      /* tp_print */
+  0,                                      /* tp_getattr */
+  0,                                      /* tp_setattr */
+  0,                                      /* tp_compare */
+  0, /* TODO */                           /* tp_repr */
+  0,                                      /* tp_as_number */
+  0,                                      /* tp_as_sequence */
+  0,                                      /* tp_as_mapping */
+  0,                                      /* tp_hash */
+  0,                                      /* tp_call */
+  0,                                      /* tp_str */
+  0,                                      /* tp_getattro */
+  0,                                      /* tp_setattro */
+  0,                                      /* tp_as_buffer */
+  Py_TPFLAGS_DEFAULT,                     /* tp_flags */
+  0,                                      /* tp_doc */
+  0,                                      /* tp_traverse */
+  0,                                      /* tp_clear */
+  0,                                      /* tp_richcompare */
+  offsetof(PyUpb_ObjWrapper, weakreflist),/* tp_weaklistoffset */
+  0,                                      /* tp_iter */
+  0,                                      /* tp_iternext */
+  PyUpb_SymbolTable_methods,              /* tp_methods */
+  0,                                      /* tp_members */
+  0,                                      /* tp_getset */
+  0,                                      /* tp_base */
+  0,                                      /* tp_dict */
+  0,                                      /* tp_descr_get */
+  0,                                      /* tp_descr_set */
+  0,                                      /* tp_dictoffset */
+  &PyUpb_SymbolTable_init,                /* tp_init */
+  0,                                      /* tp_alloc */
+  &PyUpb_SymbolTable_new,                 /* tp_new */
+  0,                                      /* tp_free */
+};
+
+
+/* Accessor and PyUpb_Message *************************************************/
+
+typedef struct {
+  PyTypeObject type;
+  PyTypeObject *alt_type;
+} PyUpb_MessageType;
+
+typedef struct {
+  PyObject_HEAD;
+  PyObject *msgdef;
+  char data[1];
+} PyUpb_Message;
+
+PyObject **PyUpb_Accessor_GetPtr(PyObject *_m, upb_value fval) {
+  PyUpb_Message *m = (PyUpb_Message*)_m;
+  const upb_fielddef *f = upb_value_getfielddef(fval);
+  return (PyObject**)&m->data[f->offset];
+}
+
+static upb_sflow_t PyUpb_Message_StartSequence(void *m, upb_value fval) {
+  PyObject **seq = PyUpb_Accessor_GetPtr(m, fval);
+  PyTypeObject *type = ((PyUpb_MessageType*)Py_TYPE(m))->alt_type;
+  if (!*seq) *seq = type->tp_alloc(type, 0);
+  upb_stdmsg_sethas(m, fval);
+  return UPB_CONTINUE_WITH(*seq);
+}
+
+static upb_sflow_t PyUpb_Message_StartSubmessage(void *m, upb_value fval) {
+  PyObject **submsg = PyUpb_Accessor_GetPtr(m, fval);
+  PyTypeObject *type = Py_TYPE(m);
+  if (!*submsg) *submsg = type->tp_alloc(type, 0);
+  upb_stdmsg_sethas(m, fval);
+  return UPB_CONTINUE_WITH(*submsg);
+}
+
+static upb_sflow_t PyUpb_Message_StartRepeatedSubmessage(void *a, upb_value fval) {
+  (void)fval;
+  PyObject **elem = upb_stdarray_append(a, sizeof(void*));
+  PyTypeObject *type = ((PyUpb_MessageType*)Py_TYPE(a))->alt_type;
+  if (!*elem) *elem = type->tp_alloc(type, 0);
+  return UPB_CONTINUE_WITH(*elem);
+}
+
+static upb_flow_t PyUpb_Message_StringValue(void *m, upb_value fval, upb_value val) {
+  PyObject **str = PyUpb_Accessor_GetPtr(m, fval);
+  if (*str) { Py_DECREF(*str); }
+  *str = PyString_FromStringAndSize(NULL, upb_value_getstrref(val)->len);
+  upb_strref_read(upb_value_getstrref(val), PyString_AsString(*str));
+  upb_stdmsg_sethas(m, fval);
+  return UPB_CONTINUE;
+}
+
+static upb_flow_t PyUpb_Message_AppendStringValue(void *a, upb_value fval, upb_value val) {
+  (void)fval;
+  PyObject **elem = upb_stdarray_append(a, sizeof(void*));
+  *elem = PyString_FromStringAndSize(NULL, upb_value_getstrref(val)->len);
+  upb_strref_read(upb_value_getstrref(val), PyString_AsString(*elem));
+  return UPB_CONTINUE;
+}
+
+#define STDMSG(type, size) static upb_accessor_vtbl vtbl = { \
+    &PyUpb_Message_StartSubmessage, \
+    &upb_stdmsg_set ## type, \
+    &PyUpb_Message_StartSequence, \
+    &PyUpb_Message_StartRepeatedSubmessage, \
+    &upb_stdmsg_set ## type ## _r, \
+    &upb_stdmsg_has, \
+    &upb_stdmsg_getptr, \
+    &upb_stdmsg_get ## type, \
+    &upb_stdmsg_seqbegin, \
+    &upb_stdmsg_ ## size ## byte_seqnext, \
+    &upb_stdmsg_seqget ## type};
+
+#define RETURN_STDMSG(type, size) { STDMSG(type, size); return &vtbl; }
+
+static upb_accessor_vtbl *PyUpb_AccessorForField(upb_fielddef *f) {
+  switch (f->type) {
+    case UPB_TYPE(DOUBLE): RETURN_STDMSG(double, 8)
+    case UPB_TYPE(FLOAT): RETURN_STDMSG(float, 4)
+    case UPB_TYPE(UINT64):
+    case UPB_TYPE(FIXED64): RETURN_STDMSG(uint64, 8)
+    case UPB_TYPE(INT64):
+    case UPB_TYPE(SFIXED64):
+    case UPB_TYPE(SINT64): RETURN_STDMSG(int64, 8)
+    case UPB_TYPE(INT32):
+    case UPB_TYPE(SINT32):
+    case UPB_TYPE(ENUM):
+    case UPB_TYPE(SFIXED32): RETURN_STDMSG(int32, 4)
+    case UPB_TYPE(UINT32):
+    case UPB_TYPE(FIXED32): RETURN_STDMSG(uint32, 4)
+    case UPB_TYPE(BOOL): { STDMSG(bool, 1); return &vtbl; }
+    case UPB_TYPE(GROUP):
+    case UPB_TYPE(MESSAGE): RETURN_STDMSG(ptr, 8)  // TODO: 32-bit
+    case UPB_TYPE(STRING):
+    case UPB_TYPE(BYTES): {
+      STDMSG(ptr, 8);
+      vtbl.set = &PyUpb_Message_StringValue;
+      vtbl.append = &PyUpb_Message_AppendStringValue;
+      return &vtbl;
+    }
+  }
+  return NULL;
+}
+
+
+/* Toplevel *******************************************************************/
+
+static PyMethodDef methods[] = {
+  {NULL, NULL}
+};
+
+// PyModule_AddObject steals a ref, but our object is statically allocated
+// and must not be deleted.
+#define PyUpb_AddType(mod, name, type) \
+  if (PyType_Ready(type) < 0) return; \
+  Py_INCREF(type); \
+  PyModule_AddObject(mod, name, (PyObject*)type);
+
+PyMODINIT_FUNC initupb(void) {
+  PyObject *mod = Py_InitModule("upb", methods);
+
+  PyUpb_AddType(mod, "FieldDef", &PyUpb_FieldDefType);
+  PyUpb_AddType(mod, "MessageDef", &PyUpb_MessageDefType);
+  PyUpb_AddType(mod, "SymbolTable", &PyUpb_SymbolTableType);
+
+  PyModule_AddIntConstant(mod, "LABEL_OPTIONAL", UPB_LABEL(OPTIONAL));
+  PyModule_AddIntConstant(mod, "LABEL_REQUIRED", UPB_LABEL(REQUIRED));
+  PyModule_AddIntConstant(mod, "LABEL_REPEATED", UPB_LABEL(REPEATED));
+
+  PyModule_AddIntConstant(mod, "TYPE_DOUBLE", UPB_TYPE(DOUBLE));
+  PyModule_AddIntConstant(mod, "TYPE_FLOAT", UPB_TYPE(FLOAT));
+  PyModule_AddIntConstant(mod, "TYPE_INT64", UPB_TYPE(INT64));
+  PyModule_AddIntConstant(mod, "TYPE_UINT64", UPB_TYPE(UINT64));
+  PyModule_AddIntConstant(mod, "TYPE_INT32", UPB_TYPE(INT32));
+  PyModule_AddIntConstant(mod, "TYPE_FIXED64", UPB_TYPE(FIXED64));
+  PyModule_AddIntConstant(mod, "TYPE_FIXED32", UPB_TYPE(FIXED32));
+  PyModule_AddIntConstant(mod, "TYPE_BOOL", UPB_TYPE(BOOL));
+  PyModule_AddIntConstant(mod, "TYPE_STRING", UPB_TYPE(STRING));
+  PyModule_AddIntConstant(mod, "TYPE_GROUP", UPB_TYPE(GROUP));
+  PyModule_AddIntConstant(mod, "TYPE_MESSAGE", UPB_TYPE(MESSAGE));
+  PyModule_AddIntConstant(mod, "TYPE_BYTES", UPB_TYPE(BYTES));
+  PyModule_AddIntConstant(mod, "TYPE_UINT32", UPB_TYPE(UINT32));
+  PyModule_AddIntConstant(mod, "TYPE_ENUM", UPB_TYPE(ENUM));
+  PyModule_AddIntConstant(mod, "TYPE_SFIXED32", UPB_TYPE(SFIXED32));
+  PyModule_AddIntConstant(mod, "TYPE_SFIXED64", UPB_TYPE(SFIXED64));
+  PyModule_AddIntConstant(mod, "TYPE_SINT32", UPB_TYPE(SINT32));
+  PyModule_AddIntConstant(mod, "TYPE_SINT64", UPB_TYPE(SINT64));
+
+  obj_cache = PyDict_New();
+  reverse_cache = PyDict_New();
+  static PyMethodDef method = {
+        "WeakRefCallback", &PyUpb_ObjCacheDeleteCallback, METH_O, NULL};
+  PyObject *pyname = PyString_FromString(method.ml_name);
+  weakref_callback = PyCFunction_NewEx(&method, NULL, pyname);
+  Py_DECREF(pyname);
+}
diff --git a/upb/bindings/python/upb/__init__.py b/upb/bindings/python/upb/__init__.py
new file mode 100644
index 0000000..e69de29
--- /dev/null
+++ b/upb/bindings/python/upb/__init__.py