# 18. using a list of lists in a function

#1

Code does not behave incorrectly but I want clarification on something. How would I go about using the .append() function for this problem. I tried it and it gives back expectedly exactly what is put into the function. If you put in [1,2,3] it appends that to the new list. The exercise seemingly hints at using it but I found that it was easier to use += to append the list.

#3

for append to work, we need a double loop, if we have a single loop:

``````n = [[1, 2, 3], [4, 5, 6, 7, 8, 9]]
def flatten(lists):
for i in lists:
print i
print flatten(n)``````

`i` will just hold the lists nested inside `n` (as you can see if you run the above code)

if you however use a double loop:

``````n = [[1, 2, 3], [4, 5, 6, 7, 8, 9]]
def flatten(lists):
for i in lists:
for j in i:
print j
print flatten(n)``````

you will get access to the inner lists, then you can use append

#4

Ah that makes sense. Thanks.

#5

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