edtlib: extract _slice() code to new helper module

This will make it more convenient to use it from multiple different
places, which we will have a need for in the future.

Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>

scripts/dts/python-devicetree/src/devicetree/_private.py

@@ -0,0 +1,30 @@
+# Copyright (c) 2019 Nordic Semiconductor ASA
+# Copyright (c) 2019 Linaro Limited
+# SPDX-License-Identifier: BSD-3-Clause
+
+"""
+Shared internal code. Do not use outside of the package.
+"""
+
+from typing import Any, Callable
+
+def _slice_helper(node: Any,    # avoids a circular import with dtlib
+                  prop_name: str, size: int, size_hint: str,
+                  err_class: Callable[..., Exception]):
+    # Splits node.props[prop_name].value into 'size'-sized chunks,
+    # returning a list of chunks. Raises err_class(...) if the length
+    # of the property is not evenly divisible by 'size'. The argument
+    # to err_class is a string which describes the error.
+    #
+    # 'size_hint' is a string shown on errors that gives a hint on how
+    # 'size' was calculated.
+
+    raw = node.props[prop_name].value
+    if len(raw) % size:
+        raise err_class(
+            f"'{prop_name}' property in {node!r} has length {len(raw)}, "
+            f"which is not evenly divisible by {size} (= {size_hint}). "
+            "Note that #*-cells properties come either from the parent node or "
+            "from the controller (in the case of 'interrupts').")
+
+    return [raw[i:i + size] for i in range(0, len(raw), size)]

scripts/dts/python-devicetree/src/devicetree/edtlib.py

@@ -83,7 +83,7 @@
 
 from devicetree.dtlib import DT, DTError, to_num, to_nums, Type
 from devicetree.grutils import Graph
-
+from devicetree._private import _slice_helper
 
 #
 # Public classes
@@ -2954,19 +2954,7 @@ def _interrupt_cells(node):
 
 
 def _slice(node, prop_name, size, size_hint):
-    # Splits node.props[prop_name].value into 'size'-sized chunks, returning a
-    # list of chunks. Raises EDTError if the length of the property is not
-    # evenly divisible by 'size'. 'size_hint' is a string shown on errors that
-    # gives a hint on how 'size' was calculated.
-
-    raw = node.props[prop_name].value
-    if len(raw) % size:
-        _err(f"'{prop_name}' property in {node!r} has length {len(raw)}, "
-             f"which is not evenly divisible by {size} (= {size_hint}). "
-             "Note that #*-cells properties come either from the parent node or "
-             "from the controller (in the case of 'interrupts').")
-
-    return [raw[i:i + size] for i in range(0, len(raw), size)]
+    return _slice_helper(node, prop_name, size, size_hint, EDTError)
 
 
 def _check_dt(dt):