On 2010-01-11 17:15 PM, wiso wrote:
I'm using a class to read some data from files:import multiprocessing from collections import defaultdict def SingleContainer(): return list() class Container(defaultdict): """ this class store odd line in self["odd"] and even line in self["even"]. It is stupid, but it's only an example. """ def __init__(self,file_name): if type(file_name) != str: raise AttributeError, "%s is not a string" % file_name defaultdict.__init__(self,SingleContainer) self.file_name = file_name self.readen_lines = 0 def read(self): f = open(self.file_name) print "start reading file %s" % self.file_name for line in f: self.readen_lines += 1 values = line.split() key = {0: "even", 1: "odd"}[self.readen_lines %2] self[key].append(values) print "readen %d lines from file %s" % (self.readen_lines, self.file_name) """ Now I want to read more than one file per times """ def do(file_name): container = Container(file_name) container.read() return container if __name__ == "__main__": file_names = ["prova_200909.log", "prova_200910.log"] pool = multiprocessing.Pool(len(file_names)) result = pool.map(do,file_names) pool.close() pool.join() print "Finish" but I got: start reading file prova_200909.log start reading file prova_200910.log readen 142 lines from file prova_200909.log readen 160 lines from file prova_200910.log Exception in thread Thread-2: Traceback (most recent call last): File "/usr/lib64/python2.6/threading.py", line 522, in __bootstrap_inner self.run() File "/usr/lib64/python2.6/threading.py", line 477, in run self.__target(*self.__args, **self.__kwargs) File "/usr/lib64/python2.6/multiprocessing/pool.py", line 259, in _handle_results task = get() File "main2.py", line 11, in __init__ raise AttributeError, "%s is not a string" % file_name AttributeError: (AttributeError('<function SingleContainer at 0x7f08b253d938> is not a string',),<class '__main__.Container'>, (<function SingleContainer at 0x7f08b253d938>,)) the problem is when pool share objects, but why is it calling Container.__init__ with a Container parameter?
When you return the container from do() in the worker process, it must be pickled in order to be sent over the socket. You did not override the implementation of the .__reduce_ex__() method, so it used defaultdict's version which passes the factory function as the first argument to the constructor.
I would recommend passing back the container.items() list instead of a Container instance as the easiest path forward.
-- Robert Kern "I have come to believe that the whole world is an enigma, a harmless enigma that is made terrible by our own mad attempt to interpret it as though it had an underlying truth." -- Umberto Eco -- http://mail.python.org/mailman/listinfo/python-list
