Sometimes you need to flatten a list of lists. The old way would be to do this using a couple of loops one inside the other. While this works, it's clutter you can do without. This tip show how you can take a list of lists and flatten it in one line using list comprehension.
The loop way
#The list of lists list_of_lists = [range(4), range(7)] flattened_list =  #flatten the lis for x in list_of_lists: for y in x: flattened_list.append(y)
List comprehension way
#The list of lists list_of_lists = [range(4), range(7)] #flatten the lists flattened_list = [y for x in list_of_lists for y in x]
This is not rocket science, but it's cleaner, and, I'm lead to believe, faster than the for loop method.
Of coarse itertools comes to the rescue,as stated below in the comments by <a href="https://coderwall.com/iromli ">iromli</a>
Which is faster than any of the above methods, and flattening lists of lists is exactly what it was designed to do.