Fix xtensor Transpose with ellipsis

pytensor/xtensor/shape.py

@@ -189,7 +189,7 @@ class Transpose(XOp):
 
 def transpose(
     x,
-    *dims: str | EllipsisType,
+    *dim: str | EllipsisType,
     missing_dims: Literal["raise", "warn", "ignore"] = "raise",
 ):
     """Transpose dimensions of the tensor.
@@ -198,7 +198,7 @@ def transpose(
     ----------
     x : XTensorVariable
         Input tensor to transpose.
-    *dims : str
+    *dim : str
         Dimensions to transpose to. Can include ellipsis (...) to represent
         remaining dimensions in their original order.
     missing_dims : {"raise", "warn", "ignore"}, optional
@@ -220,7 +220,7 @@ def transpose(
     # Validate dimensions
     x = as_xtensor(x)
     x_dims = x.type.dims
-    invalid_dims = set(dims) - {..., *x_dims}
+    invalid_dims = set(dim) - {..., *x_dims}
     if invalid_dims:
         if missing_dims != "ignore":
             msg = f"Dimensions {invalid_dims} do not exist. Expected one or more of: {x_dims}"
@@ -229,21 +229,27 @@ def transpose(
             else:
                 warnings.warn(msg)
         # Handle missing dimensions if not raising
-        dims = tuple(d for d in dims if d in x_dims or d is ...)
-
-    if dims == () or dims == (...,):
-        dims = tuple(reversed(x_dims))
-    elif ... in dims:
-        if dims.count(...) > 1:
+        dim = tuple(d for d in dim if d in x_dims or d is ...)
+
+    if dim == ():
+        dim = tuple(reversed(x_dims))
+    elif dim == (...,):
+        dim = x_dims
+    elif ... in dim:
+        if dim.count(...) > 1:
             raise ValueError("Ellipsis (...) can only appear once in the dimensions")
         # Handle ellipsis expansion
-        ellipsis_idx = dims.index(...)
-        pre = dims[:ellipsis_idx]
-        post = dims[ellipsis_idx + 1 :]
+        ellipsis_idx = dim.index(...)
+        pre = dim[:ellipsis_idx]
+        post = dim[ellipsis_idx + 1 :]
         middle = [d for d in x_dims if d not in pre + post]
-        dims = (*pre, *middle, *post)
+        dim = (*pre, *middle, *post)
+
+    if dim == x_dims:
+        # No-op transpose
+        return x
 
-    return Transpose(typing.cast(tuple[str], dims))(x)
+    return Transpose(dims=typing.cast(tuple[str], dim))(x)
 
 
 class Concat(XOp):

pytensor/xtensor/type.py

@@ -691,14 +691,14 @@ class XTensorVariable(Variable[_XTensorTypeType, OptionalApplyType]):
     # https://docs.xarray.dev/en/latest/api.html#id8
     def transpose(
         self,
-        *dims: str | EllipsisType,
+        *dim: str | EllipsisType,
         missing_dims: Literal["raise", "warn", "ignore"] = "raise",
     ):
         """Transpose dimensions of the tensor.
 
         Parameters
         ----------
-        *dims : str | Ellipsis
+        *dim : str | Ellipsis
             Dimensions to transpose. If empty, performs a full transpose.
             Can use ellipsis (...) to represent remaining dimensions.
         missing_dims : {"raise", "warn", "ignore"}, default="raise"
@@ -718,7 +718,7 @@ class XTensorVariable(Variable[_XTensorTypeType, OptionalApplyType]):
             If missing_dims="raise" and any dimensions don't exist.
             If multiple ellipsis are provided.
         """
-        return px.shape.transpose(self, *dims, missing_dims=missing_dims)
+        return px.shape.transpose(self, *dim, missing_dims=missing_dims)
 
     def stack(self, dim, **dims):
         return px.shape.stack(self, dim, **dims)

tests/xtensor/test_shape.py

@@ -15,7 +15,6 @@ from pytensor.tensor import scalar
 from pytensor.xtensor.shape import (
     concat,
     stack,
-    transpose,
     unstack,
 )
 from pytensor.xtensor.type import xtensor
@@ -46,13 +45,14 @@ def test_transpose():
     permutations = [
         (a, b, c, d, e),  # identity
         (e, d, c, b, a),  # full tranpose
-        (),  # eqivalent to full transpose
+        (),  # equivalent to full transpose
         (a, b, c, e, d),  # swap last two dims
         (..., d, c),  # equivalent to (a, b, e, d, c)
         (b, a, ..., e, d),  # equivalent to (b, a, c, d, e)
         (c, a, ...),  # equivalent to (c, a, b, d, e)
+        (...,),  # no op
     ]
-    outs = [transpose(x, *perm) for perm in permutations]
+    outs = [x.transpose(*perm) for perm in permutations]
 
     fn = xr_function([x], outs)
     x_test = xr_arange_like(x)