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Python多处理池映射:AttributeError:无法pickle本地对象

python-multiprocessing multiprocessing python

Amit · 技术社区 · 6 年前

我在一个类中有一个方法,它需要在一个循环中做大量的工作,我想把工作扩展到我所有的核心。

我写了下面的代码,如果我使用普通的 map() ,但与 pool.map() 返回一个错误。

import multiprocessing
pool = multiprocessing.Pool(multiprocessing.cpu_count() - 1)

class OtherClass:
  def run(sentence, graph):
    return False

class SomeClass:
  def __init__(self):
    self.sentences = [["Some string"]]
    self.graphs = ["string"]

  def some_method(self):
      other = OtherClass()

      def single(params):
          sentences, graph = params
          return [other.run(sentence, graph) for sentence in sentences]

      return list(pool.map(single, zip(self.sentences, self.graphs)))


SomeClass().some_method()

错误1:

AttributeError:无法pickle local object'SomeClass.someu方法…单身

为什么不能泡菜 single() 单个() 到全局模块范围(不在类内-使其独立于上下文):

import multiprocessing
pool = multiprocessing.Pool(multiprocessing.cpu_count() - 1)

class OtherClass:
  def run(sentence, graph):
    return False


def single(params):
    other = OtherClass()
    sentences, graph = params
    return [other.run(sentence, graph) for sentence in sentences]

class SomeClass:
  def __init__(self):
    self.sentences = [["Some string"]]
    self.graphs = ["string"]

  def some_method(self):
      return list(pool.map(single, zip(self.sentences, self.graphs)))


SomeClass().some_method()

错误2:

AttributeError:无法在模块上获取属性'single' 主要的 '从'/测试.py'

1 回复 | 直到 4 年前

Darkonaut 5 年前

错误1:

AttributeError:无法pickle本地对象 'SomeClass.someu方法…单身

通过移动嵌套的目标函数,您自己解决了这个错误 single() 到顶层去。

背景:

池需要pickle(序列化)它发送给其工作进程的所有内容( IPC ). 酸洗实际上只保存函数的名称,取消酸洗需要按名称重新导入函数。为此,函数需要在顶层定义,嵌套函数不会被子函数导入,并且已经尝试pickle它们会引发异常( more

错误2:

AttributeError:无法从中获取模块“main”的属性“single”

你正在启动游泳池之前 why? )它与 if __name__ == '__main__':

import multiprocessing

class OtherClass:
  def run(self, sentence, graph):
    return False


def single(params):
    other = OtherClass()
    sentences, graph = params
    return [other.run(sentence, graph) for sentence in sentences]

class SomeClass:
   def __init__(self):
       self.sentences = [["Some string"]]
       self.graphs = ["string"]

   def some_method(self):
      return list(pool.map(single, zip(self.sentences, self.graphs)))

if __name__ == '__main__':  # <- prevent RuntimeError for 'spawn'
    # and 'forkserver' start_methods
    with multiprocessing.Pool(multiprocessing.cpu_count() - 1) as pool:
        print(SomeClass().some_method())

附录

…我想把工作分散到我所有的核心。

潜在有用的背景知识 multiprocessing.Pool 分块工作:

Python multiprocessing: understanding logic behind chunksize

Marcell Pigniczki 5 年前

使用 def 声明。如果声明要在中使用的函数 Pool.map 与 global

import multiprocessing
pool = multiprocessing.Pool(multiprocessing.cpu_count() - 1)

class OtherClass:
  def run(sentence, graph):
    return False

class SomeClass:
  def __init__(self):
    self.sentences = [["Some string"]]
    self.graphs = ["string"]

  def some_method(self):
      global single  # This is ugly, but does the trick XD

      other = OtherClass()

      def single(params):
          sentences, graph = params
          return [other.run(sentence, graph) for sentence in sentences]

      return list(pool.map(single, zip(self.sentences, self.graphs)))


SomeClass().some_method()