not necesary it it 0

not necesary it it 0

https://github.com/apache/incubator-wayang/blob/77a5d3b5854f59b9cad1f9e9921b849ccc5cca58/python/src/pywy/core/core.py#L165

```python

#
# Licensed to the Apache Software Foundation (ASF) under one or more
# contributor license agreements. See the NOTICE file distributed with
# this work for additional information regarding copyright ownership.
# The ASF licenses this file to You 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.
#

from typing import Set, Iterable

from pywy.core.executor import Executor
from pywy.core.platform import Platform
from pywy.core.mapping import Mapping
from pywy.graph.graph import WayangGraph
from pywy.graph.types import WGraphOfVec, NodeOperator, NodeVec
from pywy.operators import SinkOperator

class TranslateContext:
"""TranslateContext contextual variables a parameters for the translation
"""
pass

class Plugin:
""" TODO: enrich this documentation
A plugin contributes the following components to a :class:`Context`
- mappings
- channels
- configurations
In turn, it may require several :clas:`Platform`s for its operation.
"""

platforms: Set[Platform]
mappings: Mapping
translate_context: TranslateContext

def __init__(
self,
platforms: Set[Platform],
mappings: Mapping = Mapping(),
translate_context: TranslateContext = None):
self.platforms = platforms
self.mappings = mappings
self.translate_context = translate_context

def get_mappings(self) -> Mapping:
return self.mappings

def get_executor(self) -> Executor:
pass

def __str__(self):
return "Platforms: {}, Mappings: {}".format(str(self.platforms), str(self.mappings))

def __repr__(self):
return self.__str__()

class PywyPlan:
"""A PywyPlan consists of a set of :py:class:`pywy.operators.base.PywyOperator`

the operator inside PywyPlan follow a Directed acyclic graph(DAG), and describe
how the execution needs to be performed

Attributes
----------
graph : :py:class:`pywy.graph.graph.WayangGraph`
Graph that describe the DAG, and it provides the iterable properties to
the PywyPlan
plugins : :obj:`set` of :py:class:`pywy.core.plugin.Plugin`
plugins is the set of possible platforms that can be uses to execute
the PywyPlan
sinks : :py:class:`typing.Iterable` of :py:class:`pywy.operators.sink.SinkOperator`
The list of sink operators, this describe the end of the pipeline, and
they are used to build the `graph`
"""
graph: WayangGraph

def __init__(self, plugins: Set[Plugin], sinks: Iterable[SinkOperator]):
"""basic Constructor of PywyPlan

this constructor set the plugins and sinks element, and it prepares
everything for been executed

Parameters
----------
plugins
Description of `plugins`.
sinks
Description of `sinks`.
"""
self.plugins = plugins
self.sinks = sinks
self.set_graph()

def set_graph(self):
""" it builds the :py:class:`pywy.graph.graph.WayangGraph` of the current PywyPlan
"""
self.graph = WGraphOfVec(self.sinks)

def execute(self):
""" Execute the plan with the plugin provided at the moment of creation
"""
plug = next(iter(self.plugins))
trs: Translator = Translator(plug, self)
new_plan = trs.translate()
plug.get_executor().execute(new_plan)

class Translator:
"""Translator use the :py:class:`pywy.core.Mapping` to convert the :py:class:`pywy.operators.base.PywyOperator`

Translator take a plan a produce the executable version of the plan using as tool
the :py:class:`pywy.core.Mapping` of the :py:class:`pywy.core.core.Plugin` and convert
the :py:class:`pywy.operators.base.PywyOperator` into an executable version inside
the :py:class:`pywy.core.Platform`

Attributes
----------
plugin : :py:class:`pywy.core.core.Plugin`
plugin use in the translation
plan : :py:class:`pywy.core.core.PywyPlan`
Plan to be translated by the translator
translate_context: :py:class:`pywy.core.core.TranslateContext`
context used by the translates at runtime in some case is not needed
"""

plugin: Plugin
plan: PywyPlan
translate_context: TranslateContext

def __init__(self, plugin: Plugin, plan: PywyPlan):
self.plugin = plugin
self.plan = plan
self.translate_context = plugin.translate_context

def translate(self):
mappings: Mapping = self.plugin.get_mappings()
graph = WGraphOfVec(self.plan.sinks)

translate = self.translate_context

def translate2plugin(current_op: NodeVec, next_op: NodeVec):
if current_op is None:
return

if current_op.current[1] is None:
current_op.current[1] = mappings.get_instanceof(current_op.current[0], **{'translate_context': translate})

if next_op is None:
return
if next_op.current[1] is None:
next_op.current[1] = mappings.get_instanceof(next_op.current[0], **{'translate_context': translate})

# TODO not necesary it it 0
current_op.current[1].connect(0, next_op.current[1], 0)

graph.traversal(graph.starting_nodes, translate2plugin)

node = []
for elem in graph.starting_nodes:
node.append(elem.current[1])

return PywyPlan({self.plugin}, node)

```

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