Added names function which returns attr names for an attrs class.

src/attr/__init__.py

@@ -4,6 +4,7 @@
     asdict,
     assoc,
     has,
+    names,
 )
 from ._make import (
     Attribute,
@@ -57,4 +58,5 @@
     "set_run_validators",
     "validate",
     "validators",
+    "names",
 ]

src/attr/_funcs.py

@@ -94,3 +94,18 @@ def assoc(inst, **changes):
             )
         setattr(new, k, v)
     return new
+
+
+def names(cl):
+    """
+    Returns the tuple of ``attrs`` attribute names for a class.
+
+    :param cl: Class to introspect.
+    :type cl: class
+
+    :raise TypeError: If *cl* is not a class.
+    :raise ValueError: If *cl* is not an ``attrs`` class.
+
+    :rtype: tuple of attr.ib names
+    """
+    return tuple(a.name for a in fields(cl))

tests/test_funcs.py

@@ -16,6 +16,7 @@
     asdict,
     assoc,
     has,
+    names,
 )
 from attr._make import (
     attr,
@@ -218,3 +219,57 @@ class C(object):
         assert (
             "y is not an attrs attribute on {cl!r}.".format(cl=C),
         ) == e.value.args
+
+
+class TestNames(object):
+    """
+    Tests for `names`.
+    """
+    def test_empty(self):
+        """
+        Empty classes returns empty tuple.
+        """
+        @attributes
+        class C(object):
+            pass
+
+        assert names(C) == tuple()
+
+    def test_TypeError(self):
+        """
+        Raises TypeError if argument is not a class.
+        """
+        with pytest.raises(TypeError):
+            names(1)
+
+    def test_ValueError(self):
+        """
+        Raises ValueError if argument is not an attrs class.
+        """
+        class C(object):
+            name = 'value'
+
+        with pytest.raises(ValueError):
+            names(C)
+
+    def test_attr_names(self):
+        """
+        Gives back tuple of names only for attr Attributes.
+        """
+        @attributes
+        class C(object):
+            x = attr()
+            y = attr()
+
+        assert names(C) == ('x', 'y')
+
+    def test_mixed_names(self):
+        """
+        Gives back tuple of names only for attr Attributes.
+        """
+        @attributes
+        class C(object):
+            x = attr()
+            y = 42
+
+        assert names(C) == tuple('x')