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accumulators.py
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accumulators.py
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# A large part of this module is extracted from its PySpark counterpart at
# https://spark.apache.org/docs/1.5.0/api/python/_modules/pyspark/accumulators.html
#
# 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 pysparkling import Context
>>> sc = Context()
>>> a = sc.accumulator(1)
>>> a.value
1
>>> a.value = 2
>>> a.value
2
>>> a += 5
>>> a.value
7
>>> sc.accumulator(1.0).value
1.0
>>> sc.accumulator(1j).value
1j
>>> rdd = sc.parallelize([1,2,3])
>>> def f(x):
... global a
... a += x
>>> rdd.foreach(f)
>>> a.value
13
>>> b = sc.accumulator(0)
>>> def g(x):
... b.add(x)
>>> rdd.foreach(g)
>>> b.value
6
>>> from pysparkling import AccumulatorParam
>>> class VectorAccumulatorParam(AccumulatorParam):
... def zero(self, value):
... return [0.0] * len(value)
... def addInPlace(self, val1, val2):
... for i in range(len(val1)):
... val1[i] += val2[i]
... return val1
>>> va = sc.accumulator([1.0, 2.0, 3.0], VectorAccumulatorParam())
>>> va.value
[1.0, 2.0, 3.0]
>>> def g(x):
... global va
... va += [x] * 3
>>> rdd.foreach(g)
>>> va.value
[7.0, 8.0, 9.0]
>>> sc.accumulator([1.0, 2.0, 3.0]) # doctest: +IGNORE_EXCEPTION_DETAIL
Traceback (most recent call last):
...
TypeError: No default accumulator param for type <type 'list'>
"""
__all__ = ['Accumulator', 'AccumulatorParam']
class Accumulator(object):
"""
A shared variable that can be accumulated, i.e., has a commutative and associative "add"
operation. Tasks can add values to an Accumulator with the ``+=`` operator
The API supports accumulators for primitive data types like ``int`` and
``float``, users can also define accumulators for custom types by providing a custom
``AccumulatorParam`` object. Refer to the doctest of this module for an example.
"""
def __init__(self, value, accum_param):
"""Create a new Accumulator with a given initial value and AccumulatorParam object"""
self.accum_param = accum_param
self._value = value
@property
def value(self):
return self._value
@value.setter
def value(self, value):
self._value = value
def add(self, term):
"""Adds a term to this accumulator's value"""
self._value = self.accum_param.addInPlace(self._value, term)
def __iadd__(self, term):
"""The += operator; adds a term to this accumulator's value"""
self.add(term)
return self
def __str__(self):
return str(self._value)
def __repr__(self):
return "Accumulator<value={0}>".format(self._value)
class AccumulatorParam(object):
"""
Helper object that defines how to accumulate values of a given type.
"""
def zero(self, value):
"""
Provide a "zero value" for the type, compatible in dimensions with the
provided ``value`` (e.g., a zero vector)
"""
raise NotImplementedError
def addInPlace(self, value1, value2):
"""
Add two values of the accumulator's data type, returning a new value;
for efficiency, can also update ``value1`` in place and return it.
"""
raise NotImplementedError
class AddingAccumulatorParam(AccumulatorParam):
"""
An AccumulatorParam that uses the + operators to add values. Designed for simple types
such as integers, floats, and lists. Requires the zero value for the underlying type
as a parameter.
"""
def __init__(self, zero_value):
self.zero_value = zero_value
def zero(self, value):
return self.zero_value
def addInPlace(self, value1, value2):
value1 += value2
return value1
# Singleton accumulator params for some standard types
INT_ACCUMULATOR_PARAM = AddingAccumulatorParam(0)
FLOAT_ACCUMULATOR_PARAM = AddingAccumulatorParam(0.0)
COMPLEX_ACCUMULATOR_PARAM = AddingAccumulatorParam(0.0j)
if __name__ == "__main__":
"""
Execute doctests with
$ python -m pysparkling.accumulators -v
"""
import doctest
import sys
failure_count, _ = doctest.testmod()
if failure_count:
sys.exit(-1)