如何使用具有多个参数的多处理 pool.map? [英] How to use multiprocessing pool.map with multiple arguments?
问题描述
在 Python multiprocessing
库中,是否有支持多个参数的 pool.map
变体?
In the Python multiprocessing
library, is there a variant of pool.map
which supports multiple arguments?
text = "test"
def harvester(text, case):
X = case[0]
text+ str(X)
if __name__ == '__main__':
pool = multiprocessing.Pool(processes=6)
case = RAW_DATASET
pool.map(harvester(text,case),case, 1)
pool.close()
pool.join()
推荐答案
这个问题的答案取决于版本和情况.J.F.Sebastian.1 它使用 Pool.starmap
方法,它接受一系列参数元组.然后它会自动从每个元组中解压参数并将它们传递给给定的函数:
The answer to this is version- and situation-dependent. The most general answer for recent versions of Python (since 3.3) was first described below by J.F. Sebastian.1 It uses the Pool.starmap
method, which accepts a sequence of argument tuples. It then automatically unpacks the arguments from each tuple and passes them to the given function:
import multiprocessing
from itertools import product
def merge_names(a, b):
return '{} & {}'.format(a, b)
if __name__ == '__main__':
names = ['Brown', 'Wilson', 'Bartlett', 'Rivera', 'Molloy', 'Opie']
with multiprocessing.Pool(processes=3) as pool:
results = pool.starmap(merge_names, product(names, repeat=2))
print(results)
# Output: ['Brown & Brown', 'Brown & Wilson', 'Brown & Bartlett', ...
对于早期版本的 Python,您需要编写一个辅助函数来显式解压缩参数.如果您想使用 with
,您还需要编写一个包装器来将 Pool
变成一个上下文管理器.(感谢 muon 指出这个出来.)
For earlier versions of Python, you'll need to write a helper function to unpack the arguments explicitly. If you want to use with
, you'll also need to write a wrapper to turn Pool
into a context manager. (Thanks to muon for pointing this out.)
import multiprocessing
from itertools import product
from contextlib import contextmanager
def merge_names(a, b):
return '{} & {}'.format(a, b)
def merge_names_unpack(args):
return merge_names(*args)
@contextmanager
def poolcontext(*args, **kwargs):
pool = multiprocessing.Pool(*args, **kwargs)
yield pool
pool.terminate()
if __name__ == '__main__':
names = ['Brown', 'Wilson', 'Bartlett', 'Rivera', 'Molloy', 'Opie']
with poolcontext(processes=3) as pool:
results = pool.map(merge_names_unpack, product(names, repeat=2))
print(results)
# Output: ['Brown & Brown', 'Brown & Wilson', 'Brown & Bartlett', ...
在更简单的情况下,使用固定的第二个参数,您也可以使用 partial
,但仅限于 Python 2.7+.
In simpler cases, with a fixed second argument, you can also use partial
, but only in Python 2.7+.
import multiprocessing
from functools import partial
from contextlib import contextmanager
@contextmanager
def poolcontext(*args, **kwargs):
pool = multiprocessing.Pool(*args, **kwargs)
yield pool
pool.terminate()
def merge_names(a, b):
return '{} & {}'.format(a, b)
if __name__ == '__main__':
names = ['Brown', 'Wilson', 'Bartlett', 'Rivera', 'Molloy', 'Opie']
with poolcontext(processes=3) as pool:
results = pool.map(partial(merge_names, b='Sons'), names)
print(results)
# Output: ['Brown & Sons', 'Wilson & Sons', 'Bartlett & Sons', ...
1.这其中的大部分内容都受到了他的回答的启发,而他的回答可能应该被接受.但由于这个被卡在顶部,似乎最好为未来的读者改进它.
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