2 files changed, 56 insertions, 0 deletions
diff --git a/ipalib/public.py b/ipalib/public.py
index ff8bd8b0..19a678fb 100644
--- a/ipalib/public.py
+++ b/ipalib/public.py
@@ -25,6 +25,7 @@ and UI all use.
 import re
 import inspect
 import plugable
+from plugable import lock
 import errors
 
 
@@ -39,6 +40,26 @@ def is_rule(obj):
     return callable(obj) and getattr(obj, RULE_FLAG, False) is True
 
 
+class DefaultFrom(plugable.ReadOnly):
+    def __init__(self, callback, *keys):
+        assert callable(callback), 'not a callable: %r' % callback
+        self.callback = callback
+        self.keys = keys
+        lock(self)
+
+    def __call__(self, **kw):
+        vals = tuple(kw.get(k, None) for k in self.keys)
+        if None in vals:
+            return None
+        try:
+            ret = self.callback(*vals)
+        except Exception:
+            return None
+        if isinstance(ret, basestring):
+            return ret
+        return None
+
+
 class option(plugable.Plugin):
     """
     The option class represents a kw argument from a command.
diff --git a/ipalib/tests/test_public.py b/ipalib/tests/test_public.py
index d053081d..1a496a16 100644
--- a/ipalib/tests/test_public.py
+++ b/ipalib/tests/test_public.py
@@ -63,6 +63,41 @@ def test_is_rule():
     assert not is_rule(call(None))
 
 
+class test_DefaltFrom(ClassChecker):
+    """
+    Tests the `public.DefaltFrom` class.
+    """
+    _cls = public.DefaultFrom
+
+    def test_class(self):
+        assert self.cls.__bases__ == (plugable.ReadOnly,)
+
+    def test_init(self):
+        def callback(*args):
+            return args
+        keys = ('givenname', 'sn')
+        o = self.cls(callback, *keys)
+        assert read_only(o, 'callback') is callback
+        assert read_only(o, 'keys') == keys
+
+    def test_call(self):
+        def callback(givenname, sn):
+            return givenname[0] + sn[0]
+        keys = ('givenname', 'sn')
+        o = self.cls(callback, *keys)
+        kw = dict(
+            givenname='John',
+            sn='Public',
+            hello='world',
+        )
+        assert o(**kw) == 'JP'
+        assert o() is None
+        for key in ('givenname', 'sn'):
+            kw_copy = dict(kw)
+            del kw_copy[key]
+            assert o(**kw_copy) is None
+
+
 class test_option(ClassChecker):
     """
     Tests the `public.option` class.