diff --git a/src/runtime/python/ffi.c b/src/runtime/python/ffi.c
index 2315b5537..944a615b9 100644
--- a/src/runtime/python/ffi.c
+++ b/src/runtime/python/ffi.c
@@ -323,7 +323,8 @@ match_type(PgfMarshaller *this, PgfUnmarshaller *u, PgfType ty)
     TypeObject *type = (TypeObject *)ty;
 
     Py_ssize_t n_hypos = PyList_Size(type->hypos);
-    PgfTypeHypo *hypos = alloca(sizeof(PgfTypeHypo)*n_hypos);
+    PgfTypeHypo hypos[n_hypos];
+    // PgfTypeHypo *hypos = alloca(sizeof(PgfTypeHypo)*n_hypos);
     for (Py_ssize_t i = 0; i < n_hypos; i++) {
         PyObject *hytup = (PyObject *)PyList_GetItem(type->hypos, i);
         hypos[i].bind_type = PyLong_AsLong(PyTuple_GetItem(hytup, 0));
@@ -338,7 +339,8 @@ match_type(PgfMarshaller *this, PgfUnmarshaller *u, PgfType ty)
     }
 
     Py_ssize_t n_exprs = PyList_Size(type->exprs);
-    PgfExpr *exprs = alloca(sizeof(PgfExpr)*n_exprs);
+    PgfExpr exprs[n_exprs];
+    // PgfExpr *exprs = alloca(sizeof(PgfExpr)*n_exprs);
     for (Py_ssize_t i = 0; i < n_exprs; i++) {
         exprs[i] = (PgfExpr)PyList_GetItem(type->exprs, i);
         Py_INCREF(exprs[i]);
diff --git a/src/runtime/python/pypgf.c b/src/runtime/python/pypgf.c
index cc5337886..10fb5653d 100644
--- a/src/runtime/python/pypgf.c
+++ b/src/runtime/python/pypgf.c
@@ -287,6 +287,28 @@ PGF_functionIsConstructor(PGFObject *self, PyObject *args)
     return PyBool_FromLong(isCon);
 }
 
+static PyObject *
+PGF_functionProbability(PGFObject *self, PyObject *args)
+{
+    const char *s;
+    Py_ssize_t size;
+    if (!PyArg_ParseTuple(args, "s#", &s, &size))
+        return NULL;
+
+    PgfText *funname = (PgfText *)PyMem_Malloc(sizeof(PgfText)+size+1);
+    memcpy(funname->text, s, size+1);
+    funname->size = size;
+
+    PgfExn err;
+    prob_t prob = pgf_function_prob(self->db, self->revision, funname, &err);
+    PyMem_Free(funname);
+    if (handleError(err) != PGF_EXN_NONE) {
+        return NULL;
+    }
+
+    return PyFloat_FromDouble((double)prob);
+}
+
 static PyGetSetDef PGF_getseters[] = {
     {"abstractName",
      (getter)PGF_getAbstractName, NULL,
@@ -324,6 +346,9 @@ static PyMethodDef PGF_methods[] = {
     {"functionIsConstructor", (PyCFunction)PGF_functionIsConstructor, METH_VARARGS,
      "Checks whether a function is a constructor"
     },
+    {"functionProbability", (PyCFunction)PGF_functionProbability, METH_VARARGS,
+     "Returns the probability of a function"
+    },
 
     {"newTransaction", (PyCFunction)PGF_newTransaction, METH_VARARGS,
      "Create new transaction"
diff --git a/src/runtime/python/tests/test_transactions.py b/src/runtime/python/tests/test_transactions.py
index 6e7d52a37..c2932fc90 100644
--- a/src/runtime/python/tests/test_transactions.py
+++ b/src/runtime/python/tests/test_transactions.py
@@ -1,8 +1,9 @@
 import pytest
 from pgf import *
+import math
 
 ty = readType("(N -> N) -> P (s z)")
-prob = 3.142
+prob = math.pi
 
 @pytest.fixture(scope="module")
 def gr1():
@@ -12,7 +13,7 @@ def gr1():
 def gr2(gr1):
     t = gr1.newTransaction()
     t.createFunction("foo", ty, 0, prob),
-    # t.createCategory("Q", [(BIND_TYPE_EXPLICIT, "x", ty)], prob)
+    t.createCategory("Q", [(BIND_TYPE_EXPLICIT, "x", ty)], prob)
     assert t.commit()
     return gr1
 
@@ -20,7 +21,7 @@ def gr2(gr1):
 def gr3(gr1):
     with gr1.newTransaction("bar_branch") as t:
         t.createFunction("bar", ty, 0, prob),
-        # t.createCategory("R", [(BIND_TYPE_EXPLICIT, "x", ty)], prob)
+        t.createCategory("R", [(BIND_TYPE_EXPLICIT, "x", ty)], prob)
     return gr1
 
 # gr1
@@ -35,26 +36,29 @@ def test_original_function_type(gr1):
     with pytest.raises(KeyError):
         gr1.functionType("foo")
 
-# def test_original_function_prob(gr1):
-#     with pytest.raises(KeyError):
-#         gr1.functionProbability("foo")
+def test_original_function_prob(gr1):
+    # with pytest.raises(KeyError):
+    #     gr1.functionProbability("foo")
+    assert gr1.functionProbability("foo") == float('inf')
 
 # gr2
 
 def test_extended_functions(gr2):
     assert gr2.functions == ["c", "foo", "ind", "s", "z"]
 
-# def test_extended_categories(gr2):
-#     assert gr2.categories == ["Float","Int","N","P","Q","S","String"]
-#
-# def test_extended_category_context(gr2):
-#     assert gr2.categoryContext("Q") == [(BIND_TYPE_EXPLICIT, "x", ty)]
+def test_extended_categories(gr2):
+    assert gr2.categories == ["Float","Int","N","P","Q","S","String"]
+
+def test_extended_category_context(gr2):
+    assert gr2.categoryContext("Q") == [(BIND_TYPE_EXPLICIT, "x", ty)]
 
 def test_extended_function_type(gr2):
     assert gr2.functionType("foo") == ty
 
-# def test_extended_function_prob(gr2):
-#     assert gr2.functionProbability("foo") == prob
+def test_extended_function_prob(gr2):
+    # TODO: can't we get higher precision?
+    # assert gr2.functionProbability("foo") == prob
+    assert math.isclose(gr2.functionProbability("foo"), prob, rel_tol=1e-06)
 
 # gr3
 
diff --git a/src/runtime/python/transactions.c b/src/runtime/python/transactions.c
index 3f3734d5f..b6c5db408 100644
--- a/src/runtime/python/transactions.c
+++ b/src/runtime/python/transactions.c
@@ -104,16 +104,25 @@ Transaction_createCategory(TransactionObject *self, PyObject *args)
 {
     const char *s;
     Py_ssize_t size;
+    PyObject *hypos;
     float prob = 0.0;
-    if (!PyArg_ParseTuple(args, "s#f", &s, &size, prob))
+    if (!PyArg_ParseTuple(args, "s#O!f", &s, &size, &PyList_Type, &hypos, prob))
         return NULL;
 
     PgfText *catname = (PgfText *)PyMem_Malloc(sizeof(PgfText)+size+1);
     memcpy(catname->text, s, size+1);
     catname->size = size;
 
-    Py_ssize_t n_hypos = 0;
-    PgfTypeHypo *context = NULL;
+    Py_ssize_t n_hypos = PyList_Size(hypos);
+    PgfTypeHypo context[n_hypos];
+    // PgfTypeHypo *context = alloca(sizeof(PgfTypeHypo)*n_hypos);
+    for (Py_ssize_t i = 0; i < n_hypos; i++) {
+        PyObject *hytup = (PyObject *)PyList_GetItem(hypos, i);
+        context[i].bind_type = PyLong_AsLong(PyTuple_GetItem(hytup, 0));
+        context[i].cid = PyUnicode_AsPgfText(PyTuple_GetItem(hytup, 1));
+        context[i].type = (PgfType) PyTuple_GetItem(hytup, 2);
+        Py_INCREF(context[i].type);
+    }
 
     PgfExn err;
     pgf_create_category(self->pgf->db, self->revision, catname, n_hypos, context, prob, &marshaller, &err);