Create a dictionary with list items as keys and indices as values?

Question

s =['Hello','World','Hello','World']
l = list()
for x,y in enumerate(s):
    l.append((y,x))

The output I got is [('Hello', 0), ('World', 1), ('Hello', 2), ('World', 3)]

But I want

Hello-[0,2]
World-[1,3]

Answer 1

You can use a dictionary:

d = {}
for i, v in enumerate(s):
    if v in d:
        d[v].append(i)
    else:
        d[v] = [i]

d
# {'Hello': [0, 2], 'World': [1, 3]}