Python: How to append generator iteration values to a list

generator, iteration, list, permutation, python

Solution

Your generator does not yield new lists, it yields the same list over and over again. When you append that yielded reference to `a` you only get to see the same original list, in it's most recently shuffled form, over and over again.

Yield a copy instead:

def poss_comb(coord):
    coord = coord[:]  # use a local copy of the list
    random.shuffle(coord)
    yield coord

or create a random sort instead of using inplace shuffling with the `sorted()` function:

def poss_comb(coord):
    yield sorted(coord, key=lambda k: random.random())

Problem

I have a simple generator to give me permutations of a set of coordinates. I wish to save each new permutation to an element in an array using the code below: ``` import random def poss_comb(coord): spin=random.shuffle if spin: spin(coord) yield (coord) ... a=[] for n in xrange(0,10): for item in poss_comb(coord): print item a.append(item) ``` However when printing the results printing `item` gives me what I want : ``` ['0 1', '', '1 2', '1 3'] ['0 1', '', '1 2', '1 3'] ['1 2', '0 1', '1 3', ''] ['0 1', '1 2', '', '1 3'] ['1 3', '', '1 2', '0 1'] ['1 3', '1 2', '0 1', ''] ['0 1', '', '1 3', '1 2'] ['1 2', '0 1', '', '1 3'] ['1 2', '1 3', '', '0 1'] ['', '1 2', '1 3', '0 1'] ``` whereas printing `list a` provides an array where each element is a copy of the last permutation. What would be a better way to do this?

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