在Python多处理库中,是否有支持多个参数的pool.map变体?
import multiprocessing
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()
这是我用来将多个参数传递给pool.imap fork中使用的单参数函数的例程的示例:
from multiprocessing import Pool
# Wrapper of the function to map:
class makefun:
def __init__(self, var2):
self.var2 = var2
def fun(self, i):
var2 = self.var2
return var1[i] + var2
# Couple of variables for the example:
var1 = [1, 2, 3, 5, 6, 7, 8]
var2 = [9, 10, 11, 12]
# Open the pool:
pool = Pool(processes=2)
# Wrapper loop
for j in range(len(var2)):
# Obtain the function to map
pool_fun = makefun(var2[j]).fun
# Fork loop
for i, value in enumerate(pool.imap(pool_fun, range(len(var1))), 0):
print(var1[i], '+' ,var2[j], '=', value)
# Close the pool
pool.close()
将Python 3.3+与pool.starmap()一起使用:
from multiprocessing.dummy import Pool as ThreadPool
def write(i, x):
print(i, "---", x)
a = ["1","2","3"]
b = ["4","5","6"]
pool = ThreadPool(2)
pool.starmap(write, zip(a,b))
pool.close()
pool.join()
结果:
1 --- 4
2 --- 5
3 --- 6
如果您喜欢,还可以zip()更多参数:zip(a,b,c,d,e)
如果希望将常量值作为参数传递:
import itertools
zip(itertools.repeat(constant), a)
如果您的函数应该返回以下内容:
results = pool.starmap(write, zip(a,b))
这将提供一个包含返回值的列表。
另一种方法是将列表列表传递给单参数例程:
import os
from multiprocessing import Pool
def task(args):
print "PID =", os.getpid(), ", arg1 =", args[0], ", arg2 =", args[1]
pool = Pool()
pool.map(task, [
[1,2],
[3,4],
[5,6],
[7,8]
])
然后可以用自己喜欢的方法构造一个参数列表。
更好的方法是使用修饰符,而不是手工编写包装函数。特别是当您有很多函数要映射时,装饰器将通过避免为每个函数编写包装器来节省时间。通常,修饰函数是不可选择的,但是我们可以使用functools来解决它。更多讨论可以在这里找到。
以下是示例:
def unpack_args(func):
from functools import wraps
@wraps(func)
def wrapper(args):
if isinstance(args, dict):
return func(**args)
else:
return func(*args)
return wrapper
@unpack_args
def func(x, y):
return x + y
然后你可以用压缩的参数来映射它:
np, xlist, ylist = 2, range(10), range(10)
pool = Pool(np)
res = pool.map(func, zip(xlist, ylist))
pool.close()
pool.join()
当然,您可能总是在Python3中使用Pool.starmap(>=3.3),正如其他答案中提到的那样。
Python 2的更好解决方案:
from multiprocessing import Pool
def func((i, (a, b))):
print i, a, b
return a + b
pool = Pool(3)
pool.map(func, [(0,(1,2)), (1,(2,3)), (2,(3, 4))])
输出
2 3 4
1 2 3
0 1 2
out[]:
[3, 5, 7]