improve namedbidict

- raise TypeError if base_type is not a frozenbidict subclass
- rewrite the code to be clearer

CHANGELOG.rst

@@ -79,8 +79,19 @@ Breaking API Changes
   (So it is no longer possible to create an infinite chain like
   ``DuplicationPolicy.RAISE.RAISE.RAISE...``.)
 
-- Pickling bidicts on Python 2 now requires the latest version of the
-  pickle protocol (specified via -1), e.g. ``pickle.dumps(mybidict, -1)``
+- :func:`~bidict.namedbidict` now raises :class:`TypeError` if the provided
+  ``base_type`` is not a subclass of :class:`~bidict.frozenbidict`.
+
+- Pickling ordered bidicts now requires
+  at least version 2 of the pickle protocol.
+  If you are using Python 3,
+  :attr:`pickle.DEFAULT_PROTOCOL` is 3 anyway,
+  so this will not affect you.
+  However if you are using in Python 2,
+  :attr:`~pickle.DEFAULT_PROTOCOL` is 0,
+  so you must now explicitly specify the version
+  in your :func:`pickle.dumps` calls,
+  e.g. ``pickle.dumps(ob, 2)``.
 
 
 0.14.2 (2017-12-06)

bidict/_named.py

@@ -9,6 +9,7 @@
 
 import re
 
+from ._frozen import frozenbidict
 from ._bidict import bidict
 
 
@@ -22,36 +23,42 @@ def namedbidict(typename, keyname, valname, base_type=bidict):
 
     Analagous to :func:`collections.namedtuple`.
     """
+    if not issubclass(base_type, frozenbidict):
+        raise TypeError('base_type must be a subclass of frozenbidict')
+
     for name in typename, keyname, valname:
         if not _LEGALNAMERE.match(name):
-            raise ValueError('"%s" does not match pattern %s' %
-                             (name, _LEGALNAMEPAT))
+            raise ValueError('%r does not match pattern %s' % (name, _LEGALNAMEPAT))
 
-    getfwd = lambda self: self.inv if self._isinv else self  # pylint: disable=protected-access
-    getfwd.__name__ = valname + '_for'
-    getfwd.__doc__ = u'%s forward %s: %s → %s' % (typename, base_type.__name__, keyname, valname)
+    class _Named(base_type):
 
-    getinv = lambda self: self if self._isinv else self.inv  # pylint: disable=protected-access
-    getinv.__name__ = keyname + '_for'
-    getinv.__doc__ = u'%s inverse %s: %s → %s' % (typename, base_type.__name__, valname, keyname)
+        __slots__ = ()
 
-    __reduce__ = lambda self: (
-        _make_empty, (typename, keyname, valname, base_type), self.__getstate__())
-    __reduce__.__name__ = '__reduce__'
-    __reduce__.__doc__ = 'helper for pickle'
+        def _getfwd(self):
+            return self.inv if self._isinv else self  # pylint: disable=protected-access
 
-    __dict__ = {
-        getfwd.__name__: property(getfwd),
-        getinv.__name__: property(getinv),
-        '__reduce__': __reduce__,
-    }
-    return type(typename, (base_type,), __dict__)
+        def _getinv(self):
+            return self if self._isinv else self.inv  # pylint: disable=protected-access
+
+        def __reduce__(self):
+            return (_make_empty, (typename, keyname, valname, base_type), self.__getstate__())
+
+
+    bname = base_type.__name__
+    fname = valname + '_for'
+    iname = keyname + '_for'
+    names = dict(typename=typename, bname=bname, keyname=keyname, valname=valname)
+    fdoc = u'{typename} forward {bname}: {keyname} → {valname}'.format(**names)
+    idoc = u'{typename} inverse {bname}: {valname} → {keyname}'.format(**names)
+    setattr(_Named, fname, property(_Named._getfwd, doc=fdoc))
+    setattr(_Named, iname, property(_Named._getinv, doc=idoc))
+
+    _Named.__name__ = typename
+    return _Named
 
 
 def _make_empty(typename, keyname, valname, base_type):
-    """
-    Create a named bidict with the indicated arguments and return an empty instance.
-
+    """Create a named bidict with the indicated arguments and return an empty instance.
     Used to make :func:`bidict.namedbidict` instances picklable.
     """
     cls = namedbidict(typename, keyname, valname, base_type=base_type)