Improve dtype handling for lexprs with constructors

Author: lshaw8317

src/blosc2/lazyexpr.py

@@ -2341,6 +2341,9 @@ def __init__(self, new_op):  # noqa: C901
         if value2 is None:
             if isinstance(value1, LazyExpr):
                 self.expression = value1.expression if op is None else f"{op}({value1.expression})"
+                # handle constructors which can give empty operands
+                _out = _numpy_eval_expr(f"{op}(o0)", {"o0": value1}, prefer_blosc=False)
+                self._dtype = _out.dtype
                 self.operands = value1.operands
             else:
                 if np.isscalar(value1):

tests/ndarray/test_lazyexpr.py

@@ -1365,6 +1365,10 @@ def test_str_constructors():
     a = blosc2.lazyexpr(f"b + linspace(0, 100, {np.prod(shape)}, shape={shape}, chunks={chunks})")
     assert a.shape == np.broadcast_shapes(shape, b.shape)
 
+    # failed before dtype handling improved
+    x = blosc2.lazyexpr("linspace(-1, 1, 10, shape=(1, 10))")
+    lexpr = blosc2.sin(blosc2.sqrt(x**2))
+
 
 @pytest.mark.parametrize(
     "obj",