Tuple type (#6)

conformity/fields/__init__.py

@@ -1,4 +1,4 @@
 from .basic import Base, Constant, Anything, Hashable, Boolean, Integer, Float, ByteString, UnicodeString
-from .structures import List, Dictionary, SchemalessDictionary
+from .structures import List, Dictionary, SchemalessDictionary, Tuple
 from .meta import Polymorph, ObjectInstance
 from .temporal import DateTime, Date, TimeDelta, Time, TZInfo

conformity/fields/structures.py

@@ -86,3 +86,25 @@ def errors(self, value):
                 for error in (self.value_type.errors(field) or [])
             )
         return result
+
+
+class Tuple(Base):
+    """
+    A tuple with types per element.
+    """
+
+    def __init__(self, *contents):
+        self.contents = contents
+
+    def errors(self, value):
+        if not isinstance(value, tuple):
+            return ["Not a tuple"]
+
+        result = []
+        if len(value) != len(self.contents):
+            result.append("number of elements %d doesn't match expected %d" % (len(value), len(self.contents)))
+
+        for i, (c_elem, v_elem) in enumerate(zip(self.contents, value)):
+            result.extend("Element %d: %s" % (i, error) for error in (c_elem.errors(v_elem) or []))
+
+        return result

conformity/tests/test_fields.py

@@ -15,6 +15,7 @@
     TimeDelta,
     SchemalessDictionary,
     ObjectInstance,
+    Tuple,
 )
 
 
@@ -220,3 +221,30 @@ class SomethingElse(object):
             schema.errors(SomethingElse()),
             ["not an instance of Thing"]
         )
+
+    def test_tuple(self):
+        schema = Tuple(Integer(gt=0), UnicodeString(), Constant("I love tuples"))
+
+        self.assertEqual(
+            schema.errors((1, "test", "I love tuples")),
+            []
+        )
+
+        # too short
+        self.assertEqual(
+            schema.errors((1, "test")),
+            ["number of elements 2 doesn't match expected 3"]
+        )
+
+        # too long
+        self.assertEqual(
+            schema.errors((1, "test", "I love tuples", "... and coffee")),
+            ["number of elements 4 doesn't match expected 3"]
+        )
+
+        self.assertEqual(
+            schema.errors((-1, None, "I hate tuples",)),
+            ['Element 0: Value not > 0',
+             'Element 1: Not a unicode string',
+             "Element 2: Value is not u'I love tuples'"]
+        )