diff --git a/src/runtime/python/ffi.c b/src/runtime/python/ffi.c
index 3d7ec5598..d49515ddb 100644
--- a/src/runtime/python/ffi.c
+++ b/src/runtime/python/ffi.c
@@ -58,7 +58,7 @@ PgfTypeHypo *
 PyList_AsHypos(PyObject *pylist, Py_ssize_t *n_hypos)
 {
     if (!PyList_Check(pylist)) {
-        PyErr_SetString(PyExc_TypeError, "PyList_AsHypos: must be a list");
+        PyErr_SetString(PyExc_TypeError, "hypos must be a list");
         return NULL;
     }
     Py_ssize_t n = PyList_Size(pylist);
@@ -66,29 +66,29 @@ PyList_AsHypos(PyObject *pylist, Py_ssize_t *n_hypos)
     PgfTypeHypo *hypos = PyMem_Malloc(sizeof(PgfTypeHypo)*n);
 
     for (Py_ssize_t i = 0; i < n; i++) {
-        PyObject *hytup = PyList_GetItem(pylist, i);
-        if (!PyTuple_Check(hytup)) {
-            PyErr_SetString(PyExc_TypeError, "PyList_AsHypos: item must be a tuple");
+        PyObject *tup = PyList_GetItem(pylist, i);
+        if (!PyTuple_Check(tup)) {
+            PyErr_SetString(PyExc_TypeError, "hypo must be a tuple");
             return NULL;
         }
 
-        PyObject *t0 = PyTuple_GetItem(hytup, 0);
+        PyObject *t0 = PyTuple_GetItem(tup, 0);
         if (!PyLong_Check(t0)) {
-            PyErr_SetString(PyExc_TypeError, "PyList_AsHypos: first element must be an integer");
+            PyErr_SetString(PyExc_TypeError, "first element of hypo must be an integer");
             return NULL;
         }
         hypos[i].bind_type = PyLong_AsLong(t0);
 
-        PyObject *t1 = PyTuple_GetItem(hytup, 1);
+        PyObject *t1 = PyTuple_GetItem(tup, 1);
         if (!PyUnicode_Check(t1)) {
-            PyErr_SetString(PyExc_TypeError, "PyList_AsHypos: second element must be a string");
+            PyErr_SetString(PyExc_TypeError, "second element of hypo must be a string");
             return NULL;
         }
         hypos[i].cid = PyUnicode_AsPgfText(t1);
 
-        PyObject *t2 = PyTuple_GetItem(hytup, 2);
+        PyObject *t2 = PyTuple_GetItem(tup, 2);
         if (!PyObject_TypeCheck(t2, &pgf_TypeType)) {
-            PyErr_SetString(PyExc_TypeError, "PyList_AsHypos: third element must be a Type");
+            PyErr_SetString(PyExc_TypeError, "third element of hypo must be a Type");
             return NULL;
         }
         hypos[i].type = (PgfType) t2;
@@ -247,7 +247,6 @@ dtyp(PgfUnmarshaller *this, int n_hypos, PgfTypeHypo *hypos, PgfText *cat, int n
 static void
 free_ref(PgfUnmarshaller *this, object x)
 {
-    // Py_XDECREF(x);
 }
 
 static PgfUnmarshallerVtbl unmarshallerVtbl =
diff --git a/src/runtime/python/pypgf.c b/src/runtime/python/pypgf.c
index eeb76f7d5..ff94b1292 100644
--- a/src/runtime/python/pypgf.c
+++ b/src/runtime/python/pypgf.c
@@ -353,6 +353,9 @@ static PyMethodDef PGF_methods[] = {
      "Returns the probability of a function"
     },
 
+    {"checkoutBranch", (PyCFunction)PGF_checkoutBranch, METH_VARARGS,
+     "Switch to a branch"
+    },
     {"newTransaction", (PyCFunction)PGF_newTransaction, METH_VARARGS,
      "Create new transaction"
     },
diff --git a/src/runtime/python/transactions.c b/src/runtime/python/transactions.c
index 64f1bda01..7625856a1 100644
--- a/src/runtime/python/transactions.c
+++ b/src/runtime/python/transactions.c
@@ -7,6 +7,35 @@
 #include "./ffi.h"
 #include "./transactions.h"
 
+PyObject *
+PGF_checkoutBranch(PGFObject *self, PyObject *args)
+{
+    const char *s = NULL;
+    Py_ssize_t size;
+    if (!PyArg_ParseTuple(args, "s#", &s, &size))
+        return NULL;
+
+    PgfText *name = (PgfText *)PyMem_RawMalloc(sizeof(PgfText)+size+1);
+    memcpy(name->text, s, size+1);
+    name->size = size;
+
+    PgfExn err;
+    PgfRevision rev = pgf_checkout_revision(self->db, name, &err);
+    PyMem_RawFree(name);
+    if (handleError(err) != PGF_EXN_NONE) {
+        return NULL;
+    }
+    if (rev == 0) {
+        // is this possible?
+        PyErr_SetString(PyExc_KeyError, "unknown branch name");
+        return NULL;
+    }
+
+    self->revision = rev;
+
+    Py_RETURN_TRUE;
+}
+
 TransactionObject *
 PGF_newTransaction(PGFObject *self, PyObject *args)
 {
@@ -49,7 +78,7 @@ Transaction_commit(TransactionObject *self, PyObject *args)
 
     pgf_free_revision(self->pgf->db, self->pgf->revision);
     self->pgf->revision = self->revision;
-    Py_INCREF(self->pgf->db);
+    Py_INCREF(self->pgf);
 
     Py_RETURN_NONE;
 }
diff --git a/src/runtime/python/transactions.h b/src/runtime/python/transactions.h
index d72835425..186ff1eda 100644
--- a/src/runtime/python/transactions.h
+++ b/src/runtime/python/transactions.h
@@ -14,6 +14,9 @@ typedef struct {
 
 PyTypeObject pgf_TransactionType;
 
+PyObject *
+PGF_checkoutBranch(PGFObject *self, PyObject *args);
+
 TransactionObject *
 PGF_newTransaction(PGFObject *self, PyObject *args);