Canvas: use class decorators to register types

celery/canvas.py

@@ -5,8 +5,9 @@
 
     Composing task workflows.
 
-    Documentation for these functions are in :mod:`celery`.
-    You should not import from this module directly.
+    Documentation for some of these types are in :mod:`celery`.
+    You should not import these from :mod:`celery` and not this module.
+
 
 """
 from __future__ import absolute_import
@@ -82,8 +83,9 @@ class Signature(dict):
     """Class that wraps the arguments and execution options
     for a single task invocation.
 
-    Used as the parts in a :class:`group` or to safely
-    pass tasks around as callbacks.
+    Used as the parts in a :class:`group` and other constructs,
+    or to pass tasks around as callbacks while being compatible
+    with serializers with a strict type subset.
 
     :param task: Either a task class/instance, or the name of a task.
     :keyword args: Positional arguments to apply.
@@ -282,6 +284,7 @@ class Signature(dict):
     immutable = _getitem_property('immutable')
 
 
+@Signature.register_type
 class chain(Signature):
 
     def __init__(self, *tasks, **options):
@@ -314,7 +317,6 @@ class chain(Signature):
 
     def __repr__(self):
         return ' | '.join(repr(t) for t in self.tasks)
-Signature.register_type(chain)
 
 
 class _basemap(Signature):
@@ -339,6 +341,7 @@ class _basemap(Signature):
         return cls(*cls._unpack_args(d['kwargs']), **d['options'])
 
 
+@Signature.register_type
 class xmap(_basemap):
     _task_name = 'celery.map'
 
@@ -346,9 +349,9 @@ class xmap(_basemap):
         task, it = self._unpack_args(self.kwargs)
         return '[{0}(x) for x in {1}]'.format(task.task,
                                               truncate(repr(it), 100))
-Signature.register_type(xmap)
 
 
+@Signature.register_type
 class xstarmap(_basemap):
     _task_name = 'celery.starmap'
 
@@ -356,9 +359,9 @@ class xstarmap(_basemap):
         task, it = self._unpack_args(self.kwargs)
         return '[{0}(*x) for x in {1}]'.format(task.task,
                                                truncate(repr(it), 100))
-Signature.register_type(xstarmap)
 
 
+@Signature.register_type
 class chunks(Signature):
     _unpack_args = itemgetter('task', 'it', 'n')
 
@@ -387,7 +390,6 @@ class chunks(Signature):
     @classmethod
     def apply_chunks(cls, task, it, n):
         return cls(task, it, n)()
-Signature.register_type(chunks)
 
 
 def _maybe_group(tasks):
@@ -400,6 +402,7 @@ def _maybe_group(tasks):
     return tasks
 
 
+@Signature.register_type
 class group(Signature):
 
     def __init__(self, *tasks, **options):
@@ -456,9 +459,9 @@ class group(Signature):
 
     def __repr__(self):
         return repr(self.tasks)
-Signature.register_type(group)
 
 
+Signature.register_type
 class chord(Signature):
 
     def __init__(self, header, body=None, task='celery.chord',
@@ -520,7 +523,6 @@ class chord(Signature):
 
     tasks = _getitem_property('kwargs.header')
     body = _getitem_property('kwargs.body')
-Signature.register_type(chord)
 
 
 def subtask(varies, *args, **kwargs):