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? -- http://mail.python.org/mailman/listinfo/python-list