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()

当前回答

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。

其他回答

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()

如何获取多个参数:

def f1(args):
    a, b, c = args[0] , args[1] , args[2]
    return a+b+c

if __name__ == "__main__":
    import multiprocessing
    pool = multiprocessing.Pool(4) 

    result1 = pool.map(f1, [ [1,2,3] ])
    print(result1)

将所有参数存储为元组数组。

该示例表示,通常调用函数为:

def mainImage(fragCoord: vec2, iResolution: vec3, iTime: float) -> vec3:

而是传递一个元组并解压缩参数:

def mainImage(package_iter) -> vec3:
    fragCoord = package_iter[0]
    iResolution = package_iter[1]
    iTime = package_iter[2]

预先使用循环构建元组:

package_iter = []
iResolution = vec3(nx, ny, 1)
for j in range((ny-1), -1, -1):
    for i in range(0, nx, 1):
        fragCoord: vec2 = vec2(i, j)
        time_elapsed_seconds = 10
        package_iter.append((fragCoord, iResolution, time_elapsed_seconds))

然后通过传递元组数组来执行所有using map:

array_rgb_values = []

with concurrent.futures.ProcessPoolExecutor() as executor:
    for val in executor.map(mainImage, package_iter):
        fragColor = val
        ir = clip(int(255* fragColor.r), 0, 255)
        ig = clip(int(255* fragColor.g), 0, 255)
        ib = clip(int(255* fragColor.b), 0, 255)

        array_rgb_values.append((ir, ig, ib))

我知道Python有*和**用于开箱,但我还没有尝试过。

使用高级库并发期货也比使用低级多处理库更好。

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]

这里有另一种方法,IMHO比提供的任何其他答案都更简单和优雅。

该程序有一个函数,它获取两个参数,打印它们并打印总和:

import multiprocessing

def main():

    with multiprocessing.Pool(10) as pool:
        params = [ (2, 2), (3, 3), (4, 4) ]
        pool.starmap(printSum, params)
    # end with

# end function

def printSum(num1, num2):
    mySum = num1 + num2
    print('num1 = ' + str(num1) + ', num2 = ' + str(num2) + ', sum = ' + str(mySum))
# end function

if __name__ == '__main__':
    main()

输出为:

num1 = 2, num2 = 2, sum = 4
num1 = 3, num2 = 3, sum = 6
num1 = 4, num2 = 4, sum = 8

有关更多信息,请参阅python文档:

https://docs.python.org/3/library/multiprocessing.html#module-多处理工具

特别是要检查星图功能。

我使用的是Python 3.6,我不确定这是否适用于较旧的Python版本

为什么在文档中没有这样一个非常直接的例子,我不确定。