Accept Mapping inputs for dict schemas

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 * [#539](https://github.com/alecthomas/voluptuous/pull/539): Raise `Invalid` instead of leaking `TypeError`/`ValueError` for non-numeric input to the `Number` validator
 * [#542](https://github.com/alecthomas/voluptuous/pull/542): Raise `Invalid` instead of leaking a raw `TypeError` for `Infinity`/`NaN` input to the `Number` validator
+* [#299](https://github.com/alecthomas/voluptuous/issues/299): Accept `Mapping` instances, not only `dict`, when validating dictionary schemas
 
 ## [0.16.0]
 

voluptuous/schema_builder.py

@@ -531,7 +531,7 @@ def _compile_dict(self, schema):
                 g.append(node)
 
         def validate_dict(path, data):
-            if not isinstance(data, dict):
+            if not isinstance(data, collections.abc.Mapping):
                 raise er.DictInvalid('expected a dictionary', path)
 
             errors = []
@@ -572,7 +572,7 @@ def validate_dict(path, data):
             if errors:
                 raise er.MultipleInvalid(errors)
 
-            out = data.__class__()
+            out = data.__class__() if isinstance(data, dict) else {}
             return base_validate(path, data.items(), out)
 
         return validate_dict

voluptuous/tests/tests.py

@@ -991,6 +991,25 @@ def test_schema_empty_dict():
         assert False, "Did not raise correct Invalid"
 
 
+def test_schema_accepts_mapping():
+    class QueryArgs(collections.abc.Mapping):
+        def __init__(self, data):
+            self._data = data
+
+        def __getitem__(self, key):
+            return self._data[key]
+
+        def __iter__(self):
+            return iter(self._data)
+
+        def __len__(self):
+            return len(self._data)
+
+    s = Schema({'page': Coerce(int), Optional('q', default=''): str})
+
+    assert s(QueryArgs({'page': '1'})) == {'page': 1, 'q': ''}
+
+
 def test_schema_empty_dict_key():
     """https://github.com/alecthomas/voluptuous/pull/434"""
     s = Schema({'var': []})