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如何在Python中的多进程中解决“AttributeError:__ exit__”问题?

我试图重写一些csv读取代码,以便能够在Python 3.2.2中的多个核心上运行它。我尝试使用多处理的Pool对象,我根据工作示例进行了改编(并且已经为我的项目的另一部分工作了)。我遇到了一条错误消息,我发现很难解密和排除故障。

错误:

Traceback (most recent call last):
  File "parser5_nodots_parallel.py", line 256, in <module>
    MG,ppl = csv2graph(r)
  File "parser5_nodots_parallel.py", line 245, in csv2graph
    node_chunks)
  File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/multiprocessing/pool.py", line 251, in map
    return self.map_async(func, iterable, chunksize).get()
  File "/Library/Frameworks/Python.framework/Versions/3.2/lib/python3.2/multiprocessing/pool.py", line 552, in get
    raise self._value
AttributeError: __exit__

相关代码:

import csv
import time
import datetime
import re
from operator import itemgetter
from multiprocessing import Pool
import itertools

def chunks(l,n):
    """Divide a list of nodes `l` in `n` chunks"""
    l_c = iter(l)
    while 1:
        x = Tuple(itertools.islice(l_c,n))
        if not x:
            return
        yield x

def csv2nodes(r):
    strptime = time.strptime
    mktime = time.mktime
    l = []
    ppl = set()
    pattern = re.compile(r"""[A-Za-z0-9"/]+?(?=[,\n])""")
    for row in r:
        with pattern.findall(row) as f:
            cell = int(f[3])
            id = int(f[2])
            st = mktime(strptime(f[0],'%d/%m/%Y'))
            ed = mktime(strptime(f[1],'%d/%m/%Y'))
        # collect list
        l.append([(id,cell,{1:st,2: ed})])
        # collect separate sets
        ppl.add(id)
    return (l,ppl)

def csv2graph(source):
    MG=nx.MultiGraph()
    # Remember that I use integers for Edge attributes, to save space! Dic above.
    # start: 1
    # end: 2
    p = Pool()
    node_divisor = len(p._pool)
    node_chunks = list(chunks(source,int(len(source)/int(node_divisor))))
    num_chunks = len(node_chunks)
    pedgelists = p.map(csv2nodes,
                       node_chunks)
    ll = []
    ppl = set()
    for l in pedgelists:
        ll.append(l[0])
        ppl.update(l[1])
    MG.add_edges_from(ll)
    return (MG,ppl)

with open('/Users/laszlosandor/Dropbox/peers_prisons/python/codetenus_test.txt','r') as source:
    r = source.readlines()
    MG,ppl = csv2graph(r)

解决这个问题的好方法是什么?

80
László

问题出在这一行:

with pattern.findall(row) as f:

您正在使用with语句。它需要一个具有__enter____exit__方法的对象。但pattern.findall返回一个listwith尝试存储__exit__方法,但它无法找到它,并引发错误。只是用

f = pattern.findall(row)

代替。

137
utdemir

在这种情况下,这不是提问者的问题,但是通用“AttributeError:__ exit__”的第一个故障排除步骤应该确保括号在那里,例如.

with SomeEnterExitObject() as foo:
    #works because a new object is referenced...

not

with SomeEnterExitObject as foo:
    #AttributeError because the class is referenced

不时抓住我,我最终到了这里--__-

53
Pocketsand

尝试使用时也会发生错误

with multiprocessing.Pool() as pool:
   # ...

使用太旧的Python版本(如Python 2.X)并且不支持将with与多处理池一起使用。

(有关详细信息,请参阅此答案 https://stackoverflow.com/a/25968716/1426569 至其他问题)

5
oseiskar

这个错误背后的原因是:Flask应用程序已经运行,没有关闭,在中间我们尝试通过以下方式启动另一个实例:with app.app_context():#Code我们需要使用这个语句之前确保先前正在运行的应用程序的范围已关闭。

0
SIDDHARTH SETHIA