# Using a list of lists in a function (Working, just wanted to know)

#1

I understand what to do, just not why I do it.

When I return the results of the flatten function, it asks for you to .append() in the instructions, meaning it must work in some way. When I tried it out, it gave errors, when I then tried the code on the top it worked. I wish to know why it didn't take the append. Thanks

``````n = [[1, 2, 3], [4, 5, 6, 7, 8, 9]]
def flatten(lists):
results = []
for i in range(0, len(lists)):
results = results + lists[i]
return results

print flatten(n)

n = [[1, 2, 3], [4, 5, 6, 7, 8, 9]]
def flatten(lists):
results = []
for i in range(0, len(lists)):
results.append(lists[i])
return results

print flatten(n)``````

#2

to use `append()` you need two loops to get access the elements in the inner list

given you deal with multi-dimensional list, you need the first loop to get access to the inner list, the second loop to get access to the elements in the inner list

#3

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