Firstly I would like to mention that i have a 3 gb ram.
I am working on an algorithm that is exponential in time on the nodes so for it I have in the code
perm = list( itertools.permutations(list(graph.Nodes))) # graph.Nodes is a tuple of 1 , 2 , ... n integers
which generates all the combinations of vertices in a list and then i can work on one of the permutation.
However when i run the program for 40 vertices , it gives a memory error.
Is there any simpler way in implementation via which i can generate all the combinations of the vertices and not have this error.
Try to use the iterator generated by the permutations instead of recreating a list with it :
perm_iterator = itertools.permutations(list(graph.Nodes))
for item in perm_iterator:
do_the_stuff(item)
by doing this, python will keep in memory only the currently used permutation, not all the permutations (in term of memory usage, it is really better ;) )
On the other side, once the memory problem solved, the time to treat all the permutations will be growing exponentially with the number of vertices....
It won't work. Looping over an iterator won't work either. You see, if the code in the for-loop takes 1 microsecond to run, it will take 2.587×10^34 years to run completely. (See http://www.wolframalpha.com/input/?i=40%21+microseconds+in+years)
来源：https://stackoverflow.com/questions/6503388/prevent-memory-error-in-itertools-permutation