Variant copy for lowlevel python

python/_tskitmodule.c

@@ -11306,6 +11306,9 @@ static PyTypeObject VariantGeneratorType = {
  *===================================================================
  */
 
+/* Forward declaration */
+static PyTypeObject VariantType;
+
 static int
 Variant_check_state(Variant *self)
 {
@@ -11377,7 +11380,7 @@ Variant_init(Variant *self, PyObject *args, PyObject *kwds)
             goto out;
         }
     }
-    self->variant = PyMem_Malloc(sizeof(tsk_vargen_t));
+    self->variant = PyMem_Malloc(sizeof(tsk_variant_t));
     if (self->variant == NULL) {
         PyErr_NoMemory();
         goto out;
@@ -11424,6 +11427,41 @@ Variant_decode(Variant *self, PyObject *args, PyObject *kwds)
     return ret;
 }
 
+static PyObject *
+Variant_restricted_copy(Variant *self)
+{
+    int err;
+    PyObject *ret = NULL;
+    Variant *copy = NULL;
+
+    if (Variant_check_state(self) != 0) {
+        goto out;
+    }
+    copy = (Variant *) _PyObject_New((PyTypeObject *) &VariantType);
+    if (copy == NULL) {
+        goto out;
+    }
+    copy->variant = PyMem_Malloc(sizeof(tsk_variant_t));
+    if (copy->variant == NULL) {
+        PyErr_NoMemory();
+        goto out;
+    }
+    /* Copies have no ts as a way of indicating they shouldn't be decoded
+       This is safe as the copy has no reference to the mutation state strings */
+    copy->tree_sequence = NULL;
+    err = tsk_variant_restricted_copy(self->variant, copy->variant);
+    if (err != 0) {
+        handle_library_error(err);
+        goto out;
+    }
+
+    ret = (PyObject *) copy;
+    copy = NULL;
+out:
+    Py_XDECREF(copy);
+    return ret;
+}
+
 static PyObject *
 Variant_get_site_id(Variant *self, void *closure)
 {
@@ -11498,6 +11536,10 @@ static PyMethodDef Variant_methods[] = {
         .ml_meth = (PyCFunction) Variant_decode,
         .ml_flags = METH_VARARGS | METH_KEYWORDS,
         .ml_doc = "Sets the variant's genotypes to those of a given tree and site" },
+    { .ml_name = "restricted_copy",
+        .ml_meth = (PyCFunction) Variant_restricted_copy,
+        .ml_flags = METH_NOARGS,
+        .ml_doc = "Copies the variant" },
     { NULL } /* Sentinel */
 };
 

python/tests/test_lowlevel.py

@@ -2431,6 +2431,43 @@ def test_variants_lifecycle(self):
         del variant
         assert np.array_equal(genotypes, expected)
 
+    def test_copy(self):
+        ts = self.get_example_tree_sequence(random_seed=42)
+        variant = _tskit.Variant(ts)
+        variant.decode(0)
+        # Everything below should work even if the Python ts is free'd
+        del ts
+        variant2 = variant.restricted_copy()
+        # Take a copy for comparison, then move the variant to check the copy
+        # doesn't move too
+        genotypes = variant.genotypes
+        genotypes_copy = np.array(variant.genotypes)
+        alleles = variant.alleles
+        site_id = variant.site_id
+        variant.decode(1)
+        with pytest.raises(
+            tskit.LibraryError, match="Can't decode a copy of a variant"
+        ):
+            variant2.decode(1)
+        assert site_id == variant2.site_id
+        assert alleles == variant2.alleles
+
+        # Variant should be equal to the copy we took earlier
+        assert np.array_equal(genotypes_copy, variant2.genotypes)
+        # But not equal to the un-copies genotypes anymore as they
+        # have decoded a new site as a side effect of reusing the
+        # array when decoding
+        assert not np.array_equal(genotypes, variant2.genotypes)
+
+        # Check the lifecycle of copies and copies of copies
+        del variant
+        variant3 = variant2.restricted_copy()
+        del variant2
+        assert np.array_equal(genotypes_copy, variant3.genotypes)
+        genotypes3 = variant3.genotypes
+        del variant3
+        assert np.array_equal(genotypes_copy, genotypes3)
+
 
 class TestLdCalculator(LowLevelTestCase):
     """