池映射的python字典迭代器

Question

我正在处理一套冷冻设备。我试图在字典“output”中找到每个冻结集的最小集。我有7万个frozenset，所以我正在制作这个frozenset字典的一大块，并将这个任务并行化。当我试图把这本字典作为输入传递给我的函数时，只有密钥被发送，所以我得到了错误，有人能帮我找出其中的错误。

output => {frozenset({'rfid', 'zone'}): 0, frozenset({'zone'}): 0, frozenset({'zone', 'time'}): 0}

def reduce(prob,result,output):
    print(output)
    for k in output.keys():
    #Function to do something


def reducer(prob,result,output):
    print(output)
    p = Pool(4) #number of processes = number of CPUs
    func2 = partial(reduce,prob,result)
    reduced_values= p.map( func2,output,chunksize=4)
    p.close() # no more tasks
    p.join()  # wrap up current tasks
    return reduced_values

if __name__ == '__main__':
    final = reducer(prob,result,output)

{frozenset({'rfid', 'zone'}): 0, frozenset({'zone'}): 0, frozenset({'zone', 'time'}): 0}
frozenset({'rfid', 'zone'}) 
Error : AttributeError: 'frozenset' object has no attribute 'keys'

按要求更新

from multiprocessing import Pool
from functools import partial
import itertools

output = {frozenset({'rfid', 'zone'}): 0, frozenset({'zone'}): 0, frozenset({'zone', 'time'}): 0}
prob = {'3': 0.3, '1': 0.15, '2': 0.5, '4': 0.05}
result = {'2': {frozenset({'time', 'zone'}), frozenset({'time', 'rfid'})}, '3': {frozenset({'time', 'rfid'}), frozenset({'rfid', 'zone'})}}

def reduce(prob,result,output):
    print(output)
    for k in output.keys():
        for ky,values in result.items():
            if any(k>=l for l in values):
                output[k] += sum((j for i,j in prob.items() if i == ky))
    return output


def reducer(prob,result,output):
    print(output)
    p = Pool(4) #number of processes = number of CPUs
    func2 = partial(reduce,prob,result)
    reduced_values= p.map( func2,output,chunksize=4)
    p.close() # no more tasks
    p.join()  # wrap up current tasks
    return reduced_values

if __name__ == '__main__':
    final = reducer(prob,result,output)


{frozenset({'zone', 'rfid'}): 0, frozenset({'zone'}): 0, frozenset({'time', 'zone'}): 0}
    for k in output.keys():
AttributeError: 'frozenset' object has no attribute 'keys'
frozenset({'zone', 'rfid'})

控制台中的完整错误详细信息：

{frozenset({'zone', 'time'}): 0, frozenset({'zone', 'rfid'}): 0, frozenset({'zone'}): 0}
frozenset({'zone', 'time'})
multiprocessing.pool.RemoteTraceback: 
"""
Traceback (most recent call last):
  File "F:\Python34\lib\multiprocessing\pool.py", line 119, in worker
    result = (True, func(*args, **kwds))
  File "F:\Python34\lib\multiprocessing\pool.py", line 44, in mapstar
    return list(map(*args))
  File "C:\Users\Dell\workspace\key_mining\src\variable.py", line 16, in reduce
    for k in output.keys():
AttributeError: 'frozenset' object has no attribute 'keys'
"""

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "C:\***\variable.py", line 33, in <module>
    final = reducer(prob,result,output)
  File "C:\***\variable.py", line 27, in reducer
    reduced_values= p.map( func2,output,chunksize=4)
  File "F:\Python34\lib\multiprocessing\pool.py", line 260, in map
    return self._map_async(func, iterable, mapstar, chunksize).get()
  File "F:\Python34\lib\multiprocessing\pool.py", line 599, in get
    raise self._value
AttributeError: 'frozenset' object has no attribute 'keys'

Answer 1

问题是您正在将dict对象传递给map。当map遍历output中的项时，它将执行以下操作：

for key in output:  # When you iterate over a dictionary, you just get the keys.
    func2(key)

所以每次调用func2时，包含在output中的所有内容都是字典中的一个键（afrozenset）。

根据您上面的评论，似乎您想将整个字典传递给func2，但是如果您这样做了，您实际上根本没有并行地执行任何操作。我想也许你觉得这样做

pool.map(func2, output, chunksize=4)

将导致output字典被分成四个字典，每个块被传递到func2的实例。但事实并非如此。相反，字典中的每个键都是单独发送的。

chunksize只是用来告诉pool一次通过进程间通信向每个子进程发送output中的多少个元素。它只用于内部目的；不管您使用什么chunksize，func2将只使用单个元素output调用。

如果你真的想传递一段话，你需要这样做：

# Break the output dict into 4 lists of (key, value) pairs
items = list(output.items())
chunksize = 4
chunks = [items[i:i + chunksize ] for i in range(0, len(items), chunksize)]
reduced_values= p.map(func2, chunks)

它将把(key, value)元组的列表从outputdict传递到func2。然后，在func2中，您可以将列表转换回dict：

def reduce(prob,result,output):
    output = dict(item for item in output)  # Convert back to a dict
    print(output)
    ...