Validate namedtuples as tuples

namedtuples can't be initialized with a tuple. Detect that datatype and
initialize it with *args notation.

Resolves alecthomas#230

voluptuous/schema_builder.py

@@ -106,6 +106,10 @@ def iteritems(d):
 REMOVE_EXTRA = 2  # extra keys not in schema will be excluded from output
 
 
+def _isnamedtuple(obj):
+    return isinstance(obj, tuple) and hasattr(obj, '_fields')
+
+
 class Undefined(object):
     def __nonzero__(self):
         return False
@@ -557,7 +561,11 @@ def validate_sequence(path, data):
                     errors.append(invalid)
             if errors:
                 raise er.MultipleInvalid(errors)
-            return type(data)(out)
+
+            if _isnamedtuple(data):
+                return type(data)(*out)
+            else:
+                return type(data)(out)
 
         return validate_sequence
 

voluptuous/tests/tests.py

@@ -1,4 +1,5 @@
 import copy
+import collections
 from nose.tools import assert_equal, assert_raises, assert_true
 
 from voluptuous import (
@@ -699,3 +700,14 @@ def test_number_validation_with_valid_precision_scale_yield_decimal_false():
     schema = Schema({"number" : Number(precision=6, scale=2, yield_decimal=False)})
     out_ = schema({"number": '1234.00'})
     assert_equal(out_.get("number"), '1234.00')
+
+
+def test_named_tuples_validate_as_tuples():
+    NT = collections.namedtuple('NT', ['a', 'b'])
+    nt = NT(1, 2)
+    t = (1, 2)
+
+    Schema((int, int))(nt)
+    Schema((int, int))(t)
+    Schema(NT(int, int))(nt)
+    Schema(NT(int, int))(t)