Python 如何让 Pool.map 采用 lambda 函数
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How to let Pool.map take a lambda function
提问by Peter Smit
I have the following function:
我有以下功能：
def copy_file(source_file, target_dir):
pass
Now I would like to use multiprocessingto execute this function at once:
现在我想用multiprocessing一次执行这个函数：
p = Pool(12)
p.map(lambda x: copy_file(x,target_dir), file_list)
The problem is, lambda's can't be pickled, so this fails. What is the most neat (pythonic) way to fix this?
问题是，lambda 不能被腌制，所以这失败了。解决此问题的最简洁（pythonic）方法是什么？
采纳答案by Fred Foo
Use a function object:
使用函数对象：
class Copier(object):
def __init__(self, tgtdir):
self.target_dir = tgtdir
def __call__(self, src):
copy_file(src, self.target_dir)
To run your Pool.map:
运行你的Pool.map：
p.map(Copier(target_dir), file_list)
回答by unutbu
For Python2.7+or Python3, you could use functools.partial:
对于 Python2.7+或 Python3，您可以使用functools.partial：
import functools
copier = functools.partial(copy_file, target_dir=target_dir)
p.map(copier, file_list)
回答by petRUShka
Question is a bit old but if you are still use Python 2 my answer can be useful.
问题有点老了，但如果您仍在使用 Python 2，我的回答可能会很有用。
Trick is to use part of pathosproject: multiprocessfork of multiprocessing. It get rid of annoying limitation of original multiprocess.
技巧是使用pathos项目的一部分：多进程的多进程分支。它摆脱了原始多进程的恼人限制。
Installation: pip install multiprocess
安装： pip install multiprocess
Usage:
用法：
>>> from multiprocess import Pool
>>> p = Pool(4)
>>> print p.map(lambda x: (lambda y:y**2)(x) + x, xrange(10))
[0, 2, 6, 12, 20, 30, 42, 56, 72, 90]
