Nicer way to make task out of any callable

This commit introduces taskflow.functor_task.FunctorTask class, which is
adapter that can be used to make a task from any callable. Dependencies,
revert callable, name and version can be specified at the moment of
construction.

Partially implements blueprint refactor-decorators
Change-Id: If92de20a67ea6c228abb0a78edaa837b98581646

taskflow/functor_task.py

@@ -0,0 +1,79 @@
+# -*- coding: utf-8 -*-
+
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+#    Copyright (C) 2012-2013 Yahoo! Inc. All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import inspect
+from taskflow import task as base
+
+# These arguments are ones that we will skip when parsing for requirements
+# for a function to operate (when used as a task).
+AUTO_ARGS = ('self', 'context', 'cls')
+
+
+def _take_arg(a):
+    if a in AUTO_ARGS:
+        return False
+    # In certain decorator cases it seems like we get the function to be
+    # decorated as an argument, we don't want to take that as a real argument.
+    if not isinstance(a, basestring):
+        return False
+    return True
+
+
+class FunctorTask(base.Task):
+    """Adaptor to make task from a callable
+
+    Take any callable and make a task from it.
+    """
+    @staticmethod
+    def _callable_name(function):
+        """Generate a name from callable"""
+        im_class = getattr(function, 'im_class', None)
+        if im_class is not None:
+            parts = (im_class.__module__, im_class.__name__, function.__name__)
+        else:
+            parts = (function.__module__, function.__name__)
+        return '.'.join(parts)
+
+    def __init__(self, execute_with, **kwargs):
+        name = kwargs.pop('name', None)
+        if name is None:
+            name = self._callable_name(execute_with)
+        super(FunctorTask, self).__init__(name, kwargs.pop('task_id', None))
+        self._execute_with = execute_with
+        self._revert_with = kwargs.pop('revert_with', None)
+        self.version = kwargs.pop('version', self.version)
+
+        self.requires.update(kwargs.pop('requires', ()))
+        if kwargs.pop('auto_extract', True):
+            f_args = inspect.getargspec(execute_with).args
+            self.requires.update([a for a in f_args if _take_arg(a)])
+
+        self.optional.update(kwargs.pop('optional', ()))
+        self.provides.update(kwargs.pop('provides', ()))
+        if kwargs:
+            raise TypeError('__init__() got an unexpected keyword argument %r'
+                            % kwargs.keys[0])
+
+    def __call__(self, *args, **kwargs):
+        return self._execute_with(*args, **kwargs)
+
+    def revert(self, *args, **kwargs):
+        if self._revert_with:
+            return self._revert_with(*args, **kwargs)
+        else:
+            return None

taskflow/tests/unit/test_functor_task.py

@@ -0,0 +1,67 @@
+# -*- coding: utf-8 -*-
+
+# vim: tabstop=4 shiftwidth=4 softtabstop=4
+
+#    Copyright (C) 2012-2013 Yahoo! Inc. All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import unittest2
+
+from taskflow import functor_task
+from taskflow.patterns import linear_flow
+
+
+def add(a, b):
+    return a + b
+
+
+class BunchOfFunctions(object):
+
+    def __init__(self, values):
+        self.values = values
+
+    def run_one(self, *args, **kwargs):
+        self.values.append('one')
+
+    def revert_one(self, *args, **kwargs):
+        self.values.append('revert one')
+
+    def run_fail(self, *args, **kwargs):
+        self.values.append('fail')
+        raise RuntimeError('Woot!')
+
+
+class FunctorTaskTest(unittest2.TestCase):
+
+    def test_simple(self):
+        task = functor_task.FunctorTask(add)
+        self.assertEquals(task.name, __name__ + '.add')
+
+    def test_other_name(self):
+        task = functor_task.FunctorTask(add, name='my task')
+        self.assertEquals(task.name, 'my task')
+
+    def test_it_runs(self):
+        values = []
+        bof = BunchOfFunctions(values)
+        t = functor_task.FunctorTask
+
+        flow = linear_flow.Flow('test')
+        flow.add_many((
+            t(bof.run_one, revert_with=bof.revert_one),
+            t(bof.run_fail)
+        ))
+        with self.assertRaisesRegexp(RuntimeError, '^Woot'):
+            flow.run(None)
+        self.assertEquals(values, ['one', 'fail', 'revert one'])