Better type check

Author: moomoohk

dpath/util.py

@@ -1,4 +1,4 @@
-from collections.abc import MutableMapping
+from collections.abc import MutableMapping, Sized
 from collections.abc import MutableSequence
 from dpath import options
 from dpath.exceptions import InvalidKeyName
@@ -286,13 +286,13 @@ def are_both_mutable(o1, o2):
         return False
 
     def merger(dst, src, _segments=()):
-        if not isinstance(dst, dict) or not isinstance(src, dict):
-            raise ValueError("Merger function supports dict-like objects only")
-
         for key, found in dpath.segments.kvs(src):
             # Our current path in the source.
             segments = _segments + (key,)
 
+            if not isinstance(key, Sized):
+                raise ValueError("Merger function supports dict-like objects only")
+
             if len(key) == 0 and not options.ALLOW_EMPTY_STRING_KEYS:
                 raise InvalidKeyName("Empty string keys not allowed without "
                                      "dpath.options.ALLOW_EMPTY_STRING_KEYS=True: "