Flatter list out of a nested list of lists

list_flattener.py

flat_list = [item for sublist in nested_list for item in sublist]

# if a list is variable, like [2,3,[2,3],[2,3]], you'll need a function
# this creates a generator that will do what you want
def flatten(lis):
    for item in lis:
        if isinstance(item, list) and not isinstance(item, str):
            for x in flatten(item):
                yield x
        else:
            yield item