Distinguish between size=None and size=() in RandomVariables

pytensor/link/jax/dispatch/random.py

@@ -12,6 +12,7 @@ from pytensor.graph import Constant
 from pytensor.link.jax.dispatch.basic import jax_funcify, jax_typify
 from pytensor.link.jax.dispatch.shape import JAXShapeTuple
 from pytensor.tensor.shape import Shape, Shape_i
+from pytensor.tensor.type_other import NoneTypeT
 
 
 try:
@@ -93,7 +94,6 @@ def jax_funcify_RandomVariable(op: ptr.RandomVariable, node, **kwargs):
     rv = node.outputs[1]
     out_dtype = rv.type.dtype
     static_shape = rv.type.shape
-
     batch_ndim = op.batch_ndim(node)
 
     # Try to pass static size directly to JAX
@@ -102,11 +102,10 @@ def jax_funcify_RandomVariable(op: ptr.RandomVariable, node, **kwargs):
         # Sometimes size can be constant folded during rewrites,
         # without the RandomVariable node being updated with new static types
         size_param = op.size_param(node)
-        if isinstance(size_param, Constant):
-            size_tuple = tuple(size_param.data)
-            # PyTensor uses empty size to represent size = None
-            if len(size_tuple):
-                static_size = tuple(size_param.data)
+        if isinstance(size_param, Constant) and not isinstance(
+            size_param.type, NoneTypeT
+        ):
+            static_size = tuple(size_param.data)
 
     # If one dimension has unknown size, either the size is determined
     # by a `Shape` operator in which case JAX will compile, or it is
@@ -115,9 +114,6 @@ def jax_funcify_RandomVariable(op: ptr.RandomVariable, node, **kwargs):
         assert_size_argument_jax_compatible(node)
 
         def sample_fn(rng, size, *parameters):
-            # PyTensor uses empty size to represent size = None
-            if jax.numpy.asarray(size).shape == (0,):
-                size = None
             return jax_sample_fn(op, node=node)(rng, size, out_dtype, *parameters)
 
     else:

pytensor/link/numba/dispatch/random.py

@@ -21,6 +21,7 @@ from pytensor.link.utils import (
 )
 from pytensor.tensor.basic import get_vector_length
 from pytensor.tensor.random.type import RandomStateType
+from pytensor.tensor.type_other import NoneTypeT
 
 
 class RandomStateNumbaType(types.Type):
@@ -101,9 +102,13 @@ def make_numba_random_fn(node, np_random_func):
     if not isinstance(rng_param.type, RandomStateType):
         raise TypeError("Numba does not support NumPy `Generator`s")
 
-    tuple_size = int(get_vector_length(op.size_param(node)))
+    size_param = op.size_param(node)
+    size_len = (
+        None
+        if isinstance(size_param.type, NoneTypeT)
+        else int(get_vector_length(size_param))
+    )
     dist_params = op.dist_params(node)
-    size_dims = tuple_size - max(i.ndim for i in dist_params)
 
     # Make a broadcast-capable version of the Numba supported scalar sampling
     # function
@@ -119,7 +124,7 @@ def make_numba_random_fn(node, np_random_func):
             "np_random_func",
             "numba_vectorize",
             "to_fixed_tuple",
-            "tuple_size",
+            "size_len",
             "size_dims",
             "rng",
             "size",
@@ -155,10 +160,12 @@ def {bcast_fn_name}({bcast_fn_input_names}):
         "out_dtype": out_dtype,
     }
 
-    if tuple_size > 0:
+    if size_len is not None:
+        size_dims = size_len - max(i.ndim for i in dist_params)
+
         random_fn_body = dedent(
             f"""
-        size = to_fixed_tuple(size, tuple_size)
+        size = to_fixed_tuple(size, size_len)
 
         data = np.empty(size, dtype=out_dtype)
         for i in np.ndindex(size[:size_dims]):
@@ -170,7 +177,7 @@ def {bcast_fn_name}({bcast_fn_input_names}):
             {
                 "np": np,
                 "to_fixed_tuple": numba_ndarray.to_fixed_tuple,
-                "tuple_size": tuple_size,
+                "size_len": size_len,
                 "size_dims": size_dims,
             }
         )
@@ -305,19 +312,24 @@ def numba_funcify_BernoulliRV(op, node, **kwargs):
 @numba_funcify.register(ptr.CategoricalRV)
 def numba_funcify_CategoricalRV(op: ptr.CategoricalRV, node, **kwargs):
     out_dtype = node.outputs[1].type.numpy_dtype
-    size_len = int(get_vector_length(op.size_param(node)))
+    size_param = op.size_param(node)
+    size_len = (
+        None
+        if isinstance(size_param.type, NoneTypeT)
+        else int(get_vector_length(size_param))
+    )
     p_ndim = node.inputs[-1].ndim
 
     @numba_basic.numba_njit
     def categorical_rv(rng, size, p):
-        if not size_len:
+        if size_len is None:
             size_tpl = p.shape[:-1]
         else:
             size_tpl = numba_ndarray.to_fixed_tuple(size, size_len)
             p = np.broadcast_to(p, size_tpl + p.shape[-1:])
 
         # Workaround https://github.com/numba/numba/issues/8975
-        if not size_len and p_ndim == 1:
+        if size_len is None and p_ndim == 1:
             unif_samples = np.asarray(np.random.uniform(0, 1))
         else:
             unif_samples = np.random.uniform(0, 1, size_tpl)
@@ -336,13 +348,20 @@ def numba_funcify_DirichletRV(op, node, **kwargs):
     out_dtype = node.outputs[1].type.numpy_dtype
     alphas_ndim = op.dist_params(node)[0].type.ndim
     neg_ind_shape_len = -alphas_ndim + 1
-    size_len = int(get_vector_length(op.size_param(node)))
+    size_param = op.size_param(node)
+    size_len = (
+        None
+        if isinstance(size_param.type, NoneTypeT)
+        else int(get_vector_length(size_param))
+    )
 
     if alphas_ndim > 1:
 
         @numba_basic.numba_njit
         def dirichlet_rv(rng, size, alphas):
-            if size_len > 0:
+            if size_len is None:
+                samples_shape = alphas.shape
+            else:
                 size_tpl = numba_ndarray.to_fixed_tuple(size, size_len)
                 if (
                     0 < alphas.ndim - 1 <= len(size_tpl)
@@ -350,8 +369,6 @@ def numba_funcify_DirichletRV(op, node, **kwargs):
                 ):
                     raise ValueError("Parameters shape and size do not match.")
                 samples_shape = size_tpl + alphas.shape[-1:]
-            else:
-                samples_shape = alphas.shape
 
             res = np.empty(samples_shape, dtype=out_dtype)
             alphas_bcast = np.broadcast_to(alphas, samples_shape)
@@ -365,7 +382,8 @@ def numba_funcify_DirichletRV(op, node, **kwargs):
 
         @numba_basic.numba_njit
         def dirichlet_rv(rng, size, alphas):
-            size = numba_ndarray.to_fixed_tuple(size, size_len)
+            if size_len is not None:
+                size = numba_ndarray.to_fixed_tuple(size, size_len)
             return (rng, np.random.dirichlet(alphas, size))
 
     return dirichlet_rv
@@ -404,8 +422,7 @@ def numba_funcify_choice_without_replacement(op, node, **kwargs):
 
 @numba_funcify.register(ptr.PermutationRV)
 def numba_funcify_permutation(op: ptr.PermutationRV, node, **kwargs):
-    # PyTensor uses size=() to represent size=None
-    size_is_none = op.size_param(node).type.shape == (0,)
+    size_is_none = isinstance(op.size_param(node).type, NoneTypeT)
     batch_ndim = op.batch_ndim(node)
     x_batch_ndim = node.inputs[-1].type.ndim - op.ndims_params[0]
 

pytensor/tensor/random/basic.py

@@ -914,12 +914,11 @@ class MvNormalRV(RandomVariable):
             # multivariate normals (or any other multivariate distributions),
             # so we need to implement that here
 
-            size = tuple(size or ())
-            if size:
+            if size is None:
+                mean, cov = broadcast_params([mean, cov], [1, 2])
+            else:
                 mean = np.broadcast_to(mean, size + mean.shape[-1:])
                 cov = np.broadcast_to(cov, size + cov.shape[-2:])
-            else:
-                mean, cov = broadcast_params([mean, cov], [1, 2])
 
             res = np.empty(mean.shape)
             for idx in np.ndindex(mean.shape[:-1]):
@@ -1800,13 +1799,11 @@ class MultinomialRV(RandomVariable):
     @classmethod
     def rng_fn(cls, rng, n, p, size):
         if n.ndim > 0 or p.ndim > 1:
-            size = tuple(size or ())
-
-            if size:
+            if size is None:
+                n, p = broadcast_params([n, p], [0, 1])
+            else:
                 n = np.broadcast_to(n, size)
                 p = np.broadcast_to(p, size + p.shape[-1:])
-            else:
-                n, p = broadcast_params([n, p], [0, 1])
 
             res = np.empty(p.shape, dtype=cls.dtype)
             for idx in np.ndindex(p.shape[:-1]):
@@ -2155,7 +2152,7 @@ class PermutationRV(RandomVariable):
     def rng_fn(self, rng, x, size):
         # We don't have access to the node in rng_fn :(
         x_batch_ndim = x.ndim - self.ndims_params[0]
-        batch_ndim = max(x_batch_ndim, len(size or ()))
+        batch_ndim = max(x_batch_ndim, 0 if size is None else len(size))
 
         if batch_ndim:
             # rng.permutation has no concept of batch dims

pytensor/tensor/random/op.py

@@ -16,7 +16,6 @@ from pytensor.tensor.basic import (
     as_tensor_variable,
     concatenate,
     constant,
-    get_underlying_scalar_constant_value,
     get_vector_length,
     infer_static_shape,
 )
@@ -28,7 +27,7 @@ from pytensor.tensor.random.utils import (
 )
 from pytensor.tensor.shape import shape_tuple
 from pytensor.tensor.type import TensorType
-from pytensor.tensor.type_other import NoneConst
+from pytensor.tensor.type_other import NoneConst, NoneTypeT
 from pytensor.tensor.utils import _parse_gufunc_signature, safe_signature
 from pytensor.tensor.variable import TensorVariable
 
@@ -196,10 +195,10 @@ class RandomVariable(Op):
 
     def _infer_shape(
         self,
-        size: TensorVariable,
+        size: TensorVariable | Variable,
         dist_params: Sequence[TensorVariable],
         param_shapes: Sequence[tuple[Variable, ...]] | None = None,
-    ) -> TensorVariable | tuple[ScalarVariable, ...]:
+    ) -> tuple[ScalarVariable | TensorVariable, ...]:
         """Compute the output shape given the size and distribution parameters.
 
         Parameters
@@ -225,9 +224,9 @@ class RandomVariable(Op):
                 self._supp_shape_from_params(dist_params, param_shapes=param_shapes)
             )
 
-        size_len = get_vector_length(size)
+        if not isinstance(size.type, NoneTypeT):
+            size_len = get_vector_length(size)
 
-        if size_len > 0:
             # Fail early when size is incompatible with parameters
             for i, (param, param_ndim_supp) in enumerate(
                 zip(dist_params, self.ndims_params)
@@ -281,21 +280,11 @@ class RandomVariable(Op):
 
         shape = batch_shape + supp_shape
 
-        if not shape:
-            shape = constant([], dtype="int64")
-
         return shape
 
     def infer_shape(self, fgraph, node, input_shapes):
         _, size, *dist_params = node.inputs
-        _, size_shape, *param_shapes = input_shapes
-
-        try:
-            size_len = get_vector_length(size)
-        except ValueError:
-            size_len = get_underlying_scalar_constant_value(size_shape[0])
-
-        size = tuple(size[n] for n in range(size_len))
+        _, _, *param_shapes = input_shapes
 
         shape = self._infer_shape(size, dist_params, param_shapes=param_shapes)
 
@@ -367,8 +356,8 @@ class RandomVariable(Op):
                 "The type of rng should be an instance of either RandomGeneratorType or RandomStateType"
             )
 
-        shape = self._infer_shape(size, dist_params)
-        _, static_shape = infer_static_shape(shape)
+        inferred_shape = self._infer_shape(size, dist_params)
+        _, static_shape = infer_static_shape(inferred_shape)
 
         inputs = (rng, size, *dist_params)
         out_type = TensorType(dtype=self.dtype, shape=static_shape)
@@ -396,21 +385,14 @@ class RandomVariable(Op):
 
         rng, size, *args = inputs
 
-        # If `size == []`, that means no size is enforced, and NumPy is trusted
-        # to draw the appropriate number of samples, NumPy uses `size=None` to
-        # represent that.  Otherwise, NumPy expects a tuple.
-        if np.size(size) == 0:
-            size = None
-        else:
-            size = tuple(size)
-
-        # Draw from `rng` if `self.inplace` is `True`, and from a copy of `rng`
-        # otherwise.
+        # Draw from `rng` if `self.inplace` is `True`, and from a copy of `rng` otherwise.
         if not self.inplace:
             rng = copy(rng)
 
         rng_var_out[0] = rng
 
+        if size is not None:
+            size = tuple(size)
         smpl_val = self.rng_fn(rng, *([*args, size]))
 
         if not isinstance(smpl_val, np.ndarray) or str(smpl_val.dtype) != self.dtype:
@@ -473,7 +455,9 @@ def vectorize_random_variable(
 
     original_dist_params = op.dist_params(node)
     old_size = op.size_param(node)
-    len_old_size = get_vector_length(old_size)
+    len_old_size = (
+        None if isinstance(old_size.type, NoneTypeT) else get_vector_length(old_size)
+    )
 
     original_expanded_dist_params = explicit_expand_dims(
         original_dist_params, op.ndims_params, len_old_size

pytensor/tensor/random/rewriting/basic.py

@@ -7,7 +7,7 @@ from pytensor.graph.op import compute_test_value
 from pytensor.graph.rewriting.basic import copy_stack_trace, in2out, node_rewriter
 from pytensor.scalar import integer_types
 from pytensor.tensor import NoneConst
-from pytensor.tensor.basic import constant, get_vector_length
+from pytensor.tensor.basic import constant
 from pytensor.tensor.elemwise import DimShuffle
 from pytensor.tensor.extra_ops import broadcast_to
 from pytensor.tensor.random.op import RandomVariable
@@ -20,7 +20,7 @@ from pytensor.tensor.subtensor import (
     as_index_variable,
     get_idx_list,
 )
-from pytensor.tensor.type_other import SliceType
+from pytensor.tensor.type_other import NoneTypeT, SliceType
 
 
 def is_rv_used_in_graph(base_rv, node, fgraph):
@@ -83,27 +83,27 @@ def local_rv_size_lift(fgraph, node):
 
     rng, size, *dist_params = node.inputs
 
+    if isinstance(size.type, NoneTypeT):
+        return
+
     dist_params = broadcast_params(dist_params, node.op.ndims_params)
 
-    if get_vector_length(size) > 0:
-        dist_params = [
-            broadcast_to(
-                p,
-                (
-                    tuple(size)
-                    + (
-                        tuple(p.shape)[-node.op.ndims_params[i] :]
-                        if node.op.ndims_params[i] > 0
-                        else ()
-                    )
+    dist_params = [
+        broadcast_to(
+            p,
+            (
+                tuple(size)
+                + (
+                    tuple(p.shape)[-node.op.ndims_params[i] :]
+                    if node.op.ndims_params[i] > 0
+                    else ()
                 )
-                if node.op.ndim_supp > 0
-                else size,
             )
-            for i, p in enumerate(dist_params)
-        ]
-    else:
-        return
+            if node.op.ndim_supp > 0
+            else size,
+        )
+        for i, p in enumerate(dist_params)
+    ]
 
     new_node = node.op.make_node(rng, None, *dist_params)
 
@@ -159,11 +159,10 @@ def local_dimshuffle_rv_lift(fgraph, node):
     batched_dims = rv.ndim - rv_op.ndim_supp
     batched_dims_ds_order = tuple(o for o in ds_op.new_order if o not in supp_dims)
 
-    # Make size explicit
-    missing_size_dims = batched_dims - get_vector_length(size)
-    if missing_size_dims > 0:
-        full_size = tuple(broadcast_params(dist_params, rv_op.ndims_params)[0].shape)
-        size = full_size[:missing_size_dims] + tuple(size)
+    if isinstance(size.type, NoneTypeT):
+        # Make size explicit
+        shape = tuple(broadcast_params(dist_params, rv_op.ndims_params)[0].shape)
+        size = shape[:batched_dims]
 
     # Update the size to reflect the DimShuffled dimensions
     new_size = [

pytensor/tensor/random/rewriting/jax.py

@@ -158,7 +158,7 @@ def materialize_implicit_arange_choice_without_replacement(fgraph, node):
         # No need to materialize arange
         return None
 
-    rng, size, dtype, a_scalar_param, *other_params = node.inputs
+    rng, size, a_scalar_param, *other_params = node.inputs
     if a_scalar_param.type.ndim > 0:
         # Automatic vectorization could have made this parameter batched,
         # there is no nice way to materialize a batched arange
@@ -170,7 +170,7 @@ def materialize_implicit_arange_choice_without_replacement(fgraph, node):
     # I.e., we substitute the first `()` by `(a)`
     new_props_dict["signature"] = re.sub(r"\(\)", "(a)", op.signature, 1)
     new_op = type(op)(**new_props_dict)
-    return new_op.make_node(rng, size, dtype, a_vector_param, *other_params).outputs
+    return new_op.make_node(rng, size, a_vector_param, *other_params).outputs
 
 
 random_vars_opt = SequenceDB()

pytensor/tensor/random/utils.py

@@ -9,8 +9,8 @@ import numpy as np
 from pytensor.compile.sharedvalue import shared
 from pytensor.graph.basic import Constant, Variable
 from pytensor.scalar import ScalarVariable
-from pytensor.tensor import get_vector_length
-from pytensor.tensor.basic import as_tensor_variable, cast, constant
+from pytensor.tensor import NoneConst, get_vector_length
+from pytensor.tensor.basic import as_tensor_variable, cast
 from pytensor.tensor.extra_ops import broadcast_arrays, broadcast_to
 from pytensor.tensor.math import maximum
 from pytensor.tensor.shape import shape_padleft, specify_shape
@@ -124,7 +124,7 @@ def broadcast_params(params, ndims_params):
 def explicit_expand_dims(
     params: Sequence[TensorVariable],
     ndim_params: Sequence[int],
-    size_length: int = 0,
+    size_length: int | None = None,
 ) -> list[TensorVariable]:
     """Introduce explicit expand_dims in RV parameters that are implicitly broadcasted together and/or by size."""
 
@@ -132,9 +132,7 @@ def explicit_expand_dims(
         param.type.ndim - ndim_param for param, ndim_param in zip(params, ndim_params)
     ]
 
-    if size_length:
-        # NOTE: PyTensor is currently treating zero-length size as size=None, which is not what Numpy does
-        # See: https://github.com/pymc-devs/pytensor/issues/568
+    if size_length is not None:
         max_batch_dims = size_length
     else:
         max_batch_dims = max(batch_dims, default=0)
@@ -159,30 +157,30 @@ def compute_batch_shape(params, ndims_params: Sequence[int]) -> TensorVariable:
 
 
 def normalize_size_param(
-    size: int | np.ndarray | Variable | Sequence | None,
+    shape: int | np.ndarray | Variable | Sequence | None,
 ) -> Variable:
     """Create an PyTensor value for a ``RandomVariable`` ``size`` parameter."""
-    if size is None:
-        size = constant([], dtype="int64")
-    elif isinstance(size, int):
-        size = as_tensor_variable([size], ndim=1)
-    elif not isinstance(size, np.ndarray | Variable | Sequence):
+    if shape is None or NoneConst.equals(shape):
+        return NoneConst
+    elif isinstance(shape, int):
+        shape = as_tensor_variable([shape], ndim=1)
+    elif not isinstance(shape, np.ndarray | Variable | Sequence):
         raise TypeError(
             "Parameter size must be None, an integer, or a sequence with integers."
         )
     else:
-        size = cast(as_tensor_variable(size, ndim=1, dtype="int64"), "int64")
+        shape = cast(as_tensor_variable(shape, ndim=1, dtype="int64"), "int64")
 
-        if not isinstance(size, Constant):
+        if not isinstance(shape, Constant):
             # This should help ensure that the length of non-constant `size`s
             # will be available after certain types of cloning (e.g. the kind
             # `Scan` performs)
-            size = specify_shape(size, (get_vector_length(size),))
+            shape = specify_shape(shape, (get_vector_length(shape),))
 
-    assert not any(s is None for s in size.type.shape)
-    assert size.dtype in int_dtypes
+    assert not any(s is None for s in shape.type.shape)
+    assert shape.dtype in int_dtypes
 
-    return size
+    return shape
 
 
 class RandomStream:

tests/tensor/random/rewriting/test_basic.py

@@ -30,6 +30,7 @@ from pytensor.tensor.random.rewriting import (
 from pytensor.tensor.rewriting.shape import ShapeFeature, ShapeOptimizer
 from pytensor.tensor.subtensor import AdvancedSubtensor, AdvancedSubtensor1, Subtensor
 from pytensor.tensor.type import iscalar, vector
+from pytensor.tensor.type_other import NoneConst
 
 
 no_mode = Mode("py", RewriteDatabaseQuery(include=[], exclude=[]))
@@ -44,20 +45,25 @@ def apply_local_rewrite_to_rv(
         p_pt.tag.test_value = p
         dist_params_pt.append(p_pt)
 
-    size_pt = []
-    for s in size:
-        # To test DimShuffle with dropping dims we need that size dimension to be constant
-        if s == 1:
-            s_pt = constant(np.array(1, dtype="int32"))
-        else:
-            s_pt = iscalar()
-        s_pt.tag.test_value = s
-        size_pt.append(s_pt)
+    if size is None:
+        size_pt = NoneConst
+    else:
+        size_pt = []
+        for s in size:
+            # To test DimShuffle with dropping dims we need that size dimension to be constant
+            if s == 1:
+                s_pt = constant(np.array(1, dtype="int32"))
+            else:
+                s_pt = iscalar()
+            s_pt.tag.test_value = s
+            size_pt.append(s_pt)
 
     dist_st = op_fn(dist_op(*dist_params_pt, size=size_pt, rng=rng, name=name))
 
     f_inputs = [
-        p for p in dist_params_pt + size_pt if not isinstance(p, slice | Constant)
+        p
+        for p in dist_params_pt + ([] if size is None else size_pt)
+        if not isinstance(p, slice | Constant)
     ]
 
     mode = Mode(
@@ -135,7 +141,7 @@ def test_inplace_rewrites(rv_op):
                 np.array([0.0, 1.0], dtype=config.floatX),
                 np.array(5.0, dtype=config.floatX),
             ],
-            [],
+            None,
         ),
         (
             normal,
@@ -180,7 +186,7 @@ def test_local_rv_size_lift(dist_op, dist_params, size):
         rng,
     )
 
-    assert pt.get_vector_length(new_out.owner.inputs[1]) == 0
+    assert new_out.owner.op.size_param(new_out.owner).data is None
 
 
 @pytest.mark.parametrize(
@@ -194,7 +200,7 @@ def test_local_rv_size_lift(dist_op, dist_params, size):
                 np.array([0.0, -100.0], dtype=np.float64),
                 np.array(1e-6, dtype=np.float64),
             ),
-            (),
+            None,
             1e-7,
         ),
         (
@@ -205,7 +211,7 @@ def test_local_rv_size_lift(dist_op, dist_params, size):
                 np.array(-10.0, dtype=np.float64),
                 np.array(1e-6, dtype=np.float64),
             ),
-            (),
+            None,
             1e-7,
         ),
         (
@@ -216,7 +222,7 @@ def test_local_rv_size_lift(dist_op, dist_params, size):
                 np.array(-10.0, dtype=np.float64),
                 np.array(1e-6, dtype=np.float64),
             ),
-            (),
+            None,
             1e-7,
         ),
         (
@@ -227,7 +233,7 @@ def test_local_rv_size_lift(dist_op, dist_params, size):
                 np.arange(2 * 2 * 2).reshape((2, 2, 2)).astype(config.floatX),
                 np.array(1e-6).astype(config.floatX),
             ),
-            (),
+            None,
             1e-3,
         ),
         (
@@ -440,7 +446,7 @@ def rand_bool_mask(shape, rng=None):
                 np.arange(30, dtype=config.floatX).reshape(3, 5, 2),
                 np.full((1, 5, 1), 1e-6),
             ),
-            (),
+            None,
         ),
         (
             # `size`-only slice
@@ -462,7 +468,7 @@ def rand_bool_mask(shape, rng=None):
                 np.arange(30, dtype=config.floatX).reshape(3, 5, 2),
                 np.full((1, 5, 1), 1e-6),
             ),
-            (),
+            None,
         ),
         (
             # `size`-only slice
@@ -484,7 +490,7 @@ def rand_bool_mask(shape, rng=None):
                 (0.1 - 1e-5) * np.arange(4).astype(dtype=config.floatX),
                 0.1 * np.arange(4).astype(dtype=config.floatX),
             ),
-            (),
+            None,
         ),
         # 5
         (
@@ -570,7 +576,7 @@ def rand_bool_mask(shape, rng=None):
                     dtype=config.floatX,
                 ),
             ),
-            (),
+            None,
         ),
         (
             # Univariate distribution with core-vector parameters
@@ -627,7 +633,7 @@ def rand_bool_mask(shape, rng=None):
                 np.arange(30).reshape(5, 3, 2),
                 1e-6,
             ),
-            (),
+            None,
         ),
         (
             # Multidimensional boolean indexing
@@ -638,7 +644,7 @@ def rand_bool_mask(shape, rng=None):
                 np.arange(30).reshape(5, 3, 2),
                 1e-6,
             ),
-            (),
+            None,
         ),
         (
             # Multidimensional boolean indexing
@@ -649,7 +655,7 @@ def rand_bool_mask(shape, rng=None):
                 np.arange(30).reshape(5, 3, 2),
                 1e-6,
             ),
-            (),
+            None,
         ),
         # 20
         (
@@ -661,7 +667,7 @@ def rand_bool_mask(shape, rng=None):
                 np.arange(30).reshape(5, 3, 2),
                 1e-6,
             ),
-            (),
+            None,
         ),
         (
             # Multidimensional boolean indexing
@@ -687,7 +693,7 @@ def rand_bool_mask(shape, rng=None):
                 np.arange(30).reshape(5, 3, 2),
                 1e-6,
             ),
-            (),
+            None,
         ),
         (
             # Multidimensional boolean indexing,
@@ -703,7 +709,7 @@ def rand_bool_mask(shape, rng=None):
                 np.arange(30).reshape(5, 3, 2),
                 1e-6,
             ),
-            (),
+            None,
         ),
         (
             # Multivariate distribution: indexing dips into core dimension
@@ -714,7 +720,7 @@ def rand_bool_mask(shape, rng=None):
                 np.array([[-1, 20], [300, -4000]], dtype=config.floatX),
                 np.eye(2).astype(config.floatX) * 1e-6,
             ),
-            (),
+            None,
         ),
         # 25
         (
@@ -726,7 +732,7 @@ def rand_bool_mask(shape, rng=None):
                 np.array([[-1, 20], [300, -4000]], dtype=config.floatX),
                 np.eye(2).astype(config.floatX) * 1e-6,
             ),
-            (),
+            None,
         ),
         (
             # Multivariate distribution: advanced integer indexing
@@ -740,7 +746,7 @@ def rand_bool_mask(shape, rng=None):
                 ),
                 np.eye(3, dtype=config.floatX) * 1e-6,
             ),
-            (),
+            None,
         ),
         (
             # Multivariate distribution: dummy slice "dips" into core dimension

tests/tensor/random/test_basic.py

@@ -212,7 +212,7 @@ sd_pt.tag.test_value = np.array(1.0, dtype=config.floatX)
 @pytest.mark.parametrize(
     "M, sd, size",
     [
-        (pt.as_tensor_variable(np.array(1.0, dtype=config.floatX)), sd_pt, ()),
+        (pt.as_tensor_variable(np.array(1.0, dtype=config.floatX)), sd_pt, None),
         (
             pt.as_tensor_variable(np.array(1.0, dtype=config.floatX)),
             sd_pt,
@@ -223,10 +223,10 @@ sd_pt.tag.test_value = np.array(1.0, dtype=config.floatX)
             sd_pt,
             (2, M_pt),
         ),
-        (pt.zeros((M_pt,)), sd_pt, ()),
+        (pt.zeros((M_pt,)), sd_pt, None),
         (pt.zeros((M_pt,)), sd_pt, (M_pt,)),
         (pt.zeros((M_pt,)), sd_pt, (2, M_pt)),
-        (pt.zeros((M_pt,)), pt.ones((M_pt,)), ()),
+        (pt.zeros((M_pt,)), pt.ones((M_pt,)), None),
         (pt.zeros((M_pt,)), pt.ones((M_pt,)), (2, M_pt)),
         (
             create_pytensor_param(
@@ -244,9 +244,10 @@ sd_pt.tag.test_value = np.array(1.0, dtype=config.floatX)
 )
 def test_normal_infer_shape(M, sd, size):
     rv = normal(M, sd, size=size)
-    rv_shape = list(normal._infer_shape(size or (), [M, sd], None))
+    size_pt = rv.owner.op.size_param(rv.owner)
+    rv_shape = list(normal._infer_shape(size_pt, [M, sd], None))
 
-    all_args = (M, sd, *size)
+    all_args = (M, sd, *(() if size is None else size))
     fn_inputs = [
         i
         for i in graph_inputs([a for a in all_args if isinstance(a, Variable)])
@@ -525,8 +526,8 @@ def mvnormal_test_fn(mean=None, cov=None, size=None, random_state=None):
         mean = np.array([0.0], dtype=config.floatX)
     if cov is None:
         cov = np.array([[1.0]], dtype=config.floatX)
-    if size is None:
-        size = ()
+    if size is not None:
+        size = tuple(size)
     return multivariate_normal.rng_fn(random_state, mean, cov, size)
 
 
@@ -713,19 +714,20 @@ M_pt.tag.test_value = 3
 @pytest.mark.parametrize(
     "M, size",
     [
-        (pt.ones((M_pt,)), ()),
+        (pt.ones((M_pt,)), None),
         (pt.ones((M_pt,)), (M_pt + 1,)),
         (pt.ones((M_pt,)), (2, M_pt)),
-        (pt.ones((M_pt, M_pt + 1)), ()),
+        (pt.ones((M_pt, M_pt + 1)), None),
         (pt.ones((M_pt, M_pt + 1)), (M_pt + 2, M_pt)),
         (pt.ones((M_pt, M_pt + 1)), (2, M_pt + 2, M_pt + 3, M_pt)),
     ],
 )
 def test_dirichlet_infer_shape(M, size):
     rv = dirichlet(M, size=size)
-    rv_shape = list(dirichlet._infer_shape(size or (), [M], None))
+    size_pt = rv.owner.op.size_param(rv.owner)
+    rv_shape = list(dirichlet._infer_shape(size_pt, [M], None))
 
-    all_args = (M, *size)
+    all_args = (M, *(() if size is None else size))
     fn_inputs = [
         i
         for i in graph_inputs([a for a in all_args if isinstance(a, Variable)])
@@ -1620,8 +1622,7 @@ def test_unnatural_batched_dims(batch_dims_tester):
 
 @config.change_flags(compute_test_value="off")
 def test_pickle():
-    # This is an interesting `Op` case, because it has `None` types and a
-    # conditional dtype
+    # This is an interesting `Op` case, because it has a conditional dtype
     sample_a = choice(5, replace=False, size=(2, 3))
 
     a_pkl = pickle.dumps(sample_a)

tests/tensor/random/test_op.py

@@ -69,7 +69,7 @@ def test_RandomVariable_basics(strict_test_value_flags):
 
     # `RandomVariable._infer_shape` should handle no parameters
     rv_shape = rv._infer_shape(pt.constant([]), (), [])
-    assert rv_shape.equals(pt.constant([], dtype="int64"))
+    assert rv_shape == ()
 
     # `dtype` is respected
     rv = RandomVariable("normal", signature="(),()->()", dtype="int32")
@@ -299,3 +299,16 @@ def test_vectorize():
     vect_node = vectorize_graph(out, {mu: new_mu, sigma: new_sigma}).owner
     assert isinstance(vect_node.op, NormalRV)
     assert vect_node.default_output().type.shape == (10, 2, 5)
+
+
+def test_size_none_vs_empty():
+    rv = RandomVariable(
+        "normal",
+        signature="(),()->()",
+    )
+    assert rv([0], [1], size=None).type.shape == (1,)
+
+    with pytest.raises(
+        ValueError, match="Size length is incompatible with batched dimensions"
+    ):
+        rv([0], [1], size=())