Peter Smit Peter Smit - 5 months ago 18
Python Question

How to let Pool.map take a lambda function

I the following function

def copy_file(source_file, target_dir):
pass


Now I would like to use multiprocessing to execute this function at once

p = new 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?

Answer

Use a function object:

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:

p.map(Copier(target_dir), file_list)
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