Question

This is as much as I know how to do, not sure if I’m doing it correctly.

L = [4, 10, 4, 2, 9, 5, 4 ]

n = len(L)
element = ()


if element in L:
    print(element)

print("number occurs in list at the following position, if element not in list")
print("this number does not occur in the list")

How do I go about getting elements that appear more than once, to print as

4 occurs in L at the following positions:  [0, 2, 6]

Answer 1

You could use a list comprehension:

>>> L = [4, 10, 4, 2, 9, 5, 4]
>>> [i for i,x in enumerate(L) if x==4]
[0, 2, 6]

enumerate(L) gives you an iterator over L that yields a tuple (index, value) for each element of L. So what I’m doing here is take each index (i) if the value (x) equals 4, and construct a list from them. No need to look at the length of the list.