Add bases argument to make_class (#152)

Fixes #152

CHANGELOG.rst

@@ -8,6 +8,7 @@ The third digit is only for regressions.
 17.1.0 (UNRELEASED)
 -------------------
 
+
 Backward-incompatible changes:
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
@@ -49,6 +50,8 @@ Changes:
 - Validators can now be defined conveniently inline by using the attribute as a decorator.
   Check out the `examples <https://attrs.readthedocs.io/en/stable/examples.html#validators>`_ to see it in action!
   `#143 <https://github.com/python-attrs/attrs/issues/143>`_
+- ``attr.make_class`` now accepts the new keyword argument ``bases`` which allows for subclassing.
+  `#152 <https://github.com/python-attrs/attrs/pull/152>`_
 
 
 ----

docs/examples.rst

@@ -607,6 +607,17 @@ You can still have power over the attributes if you pass a dictionary of name: `
    >>> i.y
    []
 
+If you need to dynamically make a class with :func:`attr.make_class` and it needs to be a subclass of something else than ``object``, use the ``bases`` argument:
+
+.. doctest::
+
+  >>> class D(object):
+  ...    def __eq__(self, other):
+  ...        return True  # arbitrary example
+  >>> C = attr.make_class("C", {}, bases=(D,), cmp=False)
+  >>> isinstance(C(), D)
+  True
+
 Sometimes, you want to have your class's ``__init__`` method do more than just
 the initialization, validation, etc. that gets done for you automatically when
 using ``@attr.s``.

src/attr/_make.py

@@ -945,7 +945,7 @@ class Factory(object):
     factory = attr()
 
 
-def make_class(name, attrs, **attributes_arguments):
+def make_class(name, attrs, bases=(object,), **attributes_arguments):
     """
     A quick way to create a new class called *name* with *attrs*.
 
@@ -956,10 +956,14 @@ def make_class(name, attrs, **attributes_arguments):
         attributes.
     :type attrs: :class:`list` or :class:`dict`
 
+    :param tuple bases: Classes that the new class will subclass.
+
     :param attributes_arguments: Passed unmodified to :func:`attr.s`.
 
     :return: A new class with *attrs*.
     :rtype: type
+
+    ..  versionadded:: 17.1.0 *bases*
     """
     if isinstance(attrs, dict):
         cls_dict = attrs
@@ -968,4 +972,4 @@ def make_class(name, attrs, **attributes_arguments):
     else:
         raise TypeError("attrs argument must be a dict or a list.")
 
-    return attributes(**attributes_arguments)(type(name, (object,), cls_dict))
+    return attributes(**attributes_arguments)(type(name, bases, cls_dict))

tests/test_make.py

@@ -432,6 +432,20 @@ def test_catches_wrong_attrs_type(self):
             "attrs argument must be a dict or a list.",
         ) == e.value.args
 
+    def test_bases(self):
+        """
+        Parameter bases default to (object,) and subclasses correctly
+        """
+        class D(object):
+            pass
+
+        cls = make_class("C", {})
+        assert cls.__mro__[-1] == object
+
+        cls = make_class("C", {}, bases=(D,))
+        assert D in cls.__mro__
+        assert isinstance(cls(), D)
+
 
 class TestFields(object):
     """