Add slicing to string lazyexprs

Author: Luke Shaw

src/blosc2/lazyexpr.py

@@ -116,7 +116,7 @@ def ne_evaluate(expression, local_dict=None, **kwargs):
 constructors = ("arange", "linspace", "fromiter", "zeros", "ones", "empty", "full", "frombuffer")
 # Note that, as reshape is accepted as a method too, it should always come last in the list
 constructors += ("reshape",)
-reducers = ("sum", "prod", "min", "max", "std", "mean", "var", "any", "all")
+reducers = ("sum", "prod", "min", "max", "std", "mean", "var", "any", "all", "slice")
 
 functions = [
     "sin",
@@ -551,7 +551,20 @@ def compute_smaller_slice(larger_shape, smaller_shape, larger_slice):
 _blacklist_re = re.compile("|".join(validation_patterns))
 
 # Define valid method names
-valid_methods = {"sum", "prod", "min", "max", "std", "mean", "var", "any", "all", "where", "reshape"}
+valid_methods = {
+    "sum",
+    "prod",
+    "min",
+    "max",
+    "std",
+    "mean",
+    "var",
+    "any",
+    "all",
+    "where",
+    "reshape",
+    "slice",
+}
 valid_methods |= {"int8", "int16", "int32", "int64", "uint8", "uint16", "uint32", "uint64"}
 valid_methods |= {"float32", "float64", "complex64", "complex128"}
 valid_methods |= {"bool", "str", "bytes"}
@@ -2534,6 +2547,7 @@ def find_args(expr):
     def _compute_expr(self, item, kwargs):  # noqa: C901
         if any(method in self.expression for method in reducers):
             # We have reductions in the expression (probably coming from a string lazyexpr)
+            # Also includes slice
             _globals = get_expr_globals(self.expression)
             lazy_expr = eval(self.expression, _globals, self.operands)
             if not isinstance(lazy_expr, blosc2.LazyExpr):

tests/ndarray/test_reductions.py

@@ -428,3 +428,11 @@ def test_reduction_index():
     assert arr[:10].shape == (10,)
     assert arr[0].shape == (1,)
     assert arr.shape == newarr.shape
+
+
+def test_slice_in_lazy():
+    shape = (20, 20)
+    a = blosc2.linspace(0, 20, num=np.prod(shape), shape=shape)
+    arr = blosc2.lazyexpr("anarr.slice(slice(10,15)) + 1", {"anarr": a})
+    newarr = arr.compute()
+    np.testing.assert_allclose(newarr[:], a.slice(slice(10, 15))[:] + 1)