Flattens a list, by spreading its elements into a new list.
list.extend()if the element is a list,
def spread(arg): ret =  for i in arg: ret.extend(i) if isinstance(i, list) else ret.append(i) return ret
spread([1, 2, 3, [4, 5, 6], , 8, 9]) # [1, 2, 3, 4, 5, 6, 7, 8, 9]
Merges two or more lists into a list of lists, combining elements from each of the input lists based on their positions.
Groups the elements of a list based on the given function and returns the count of elements in each group.
Groups the elements of a list based on the given function.