>>>>> "psaff...@googlemail.com" <psaff...@googlemail.com> (P) wrote:
>P> I'm trying to get to grips with the multiprocessing module, having >P> only used ParallelPython before. >P> based on this example: >P> http://docs.python.org/library/multiprocessing.html#using-a-pool-of-workers >P> what happens if I want my "f" to take more than one argument? I want >P> to have a list of tuples of arguments and have these correspond the >P> arguments in f, but it keeps complaining that I only have one argument >P> (the tuple). Do I have to pass in a tuple and break it up inside f? I >P> can't use multiple input lists, as I would with regular map. You give the tuple of the arguments for the function: def f(a, b, c): return a + b * c pool = Pool(processes=4) # start 4 worker processes result = pool.apply(f, (2, 3, 4)) # evaluate "f(2, 3, 4)" Or if you have a list: args = [ (2, 3, 4), # arguments for call 1 (5, 6, 7) # arguments for call 2 ] print [pool.apply(f, a) for a in args] However, as each call to apply wait for its results, this will execute sequentially instead of parallel. You can't use map directly as it works only with single argument functions. >>> print pool.map(f, args) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/multiprocessing/pool.py", line 148, in map return self.map_async(func, iterable, chunksize).get() File "/Library/Frameworks/Python.framework/Versions/2.6/lib/python2.6/multiprocessing/pool.py", line 422, in get raise self._value TypeError: f() takes exactly 3 arguments (1 given) Is that what you mean? But you can use a wrapper function: def wrapf(abc): return f(*abc) [later...] print pool.map(wrapf, args) This is covered in the examples section of multiprocessing (see calculate and calculatestar for example). Or you can use apply_async and later wait for the results: results = [pool.apply_async(f, a) for a in args] print [r.get() for r in results] Now the calls to f are done in parallel, which you can check by putting a sleep inside f. -- Piet van Oostrum <p...@cs.uu.nl> URL: http://pietvanoostrum.com [PGP 8DAE142BE17999C4] Private email: p...@vanoostrum.org -- http://mail.python.org/mailman/listinfo/python-list
