The document describes a "multilevel" list called HAIRY that contains other lists as elements. It presents a problem to write a function called flatten that takes a possibly multi-level list as an argument and returns a new single-level list containing the same elements in the same overall order. The function is demonstrated by flattening HAIRY into a single list of its elements.

1. Lists can contain other lists as elements. For example the list
HAIRY=[1,2,[3,4,[5,[6,7.8],[9,10]],11,[12,[13,14],[15,16]]]] contains several lists containing
other lists -- ie it is a "multilevel" list. Write a function flatten(L) which takes a possibly multi-
level list L as an argument and returns a new list with the same elements in the same overall
order as L but with only one level. For example, flatten(HAIRY) would return the list
[1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16]
Solution
Please find the required program along with its output. Please see the comments against each line
to understand the step.
def flatten(L): #recursive function to flatten a list
for element in L: #iterate through each element of a list
if not isinstance(element, list): # if the element is not a list,
yield element # just return the element
else: #if the element is a list, then recursivley call the flatten fucntion on the sub list, and return
each element individually
for x in flatten(element):
yield x
print "Flattened list elements are: "
for x in flatten([1,2,[3,4,[5,[6,7,8],[9,10]],11,[12,[13,14],[15,16]]]]):
print x, #print the flatten list elements
----------------------------------------
OUTPUT :
Flattened list elements
are:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16