I am sorry that I can't reproduce the error with a simpler example, and my code is too complicated to post. If I run the program in IPython shell instead of the regular Python, things work out well. I looked up some previous notes on this problem. They were all caused by using pool to call function defined within a class function. But this is not the case for me. Exception in thread Thread-3: Trac
![Python multiprocessing PicklingError: Can't pickle <type 'function'>](https://cdn-ak-scissors.b.st-hatena.com/image/square/98d6f053a97a87156775f60757c60865d0f2c47d/height=288;version=1;width=512/https%3A%2F%2Fcdn.sstatic.net%2FSites%2Fstackoverflow%2FImg%2Fapple-touch-icon%402.png%3Fv%3D73d79a89bded)