Question

I need to take a list and use a dictionary to catalogue where a particular item occurs in a list, as an example:

L = [‘a’, ‘b’, ‘c’, ‘b’, ‘c’, ‘a’, ‘e’]

the dictionary needs to contain the following:

D = {‘a’: 0, 5 , ‘b’: 1, 3 , ‘c’: 2, 4 , ‘e’: 6}

However if I use what I wrote:

for i in range(len(word_list)):
    if D.has_key('word_list[i]') == False:
        D['word_list[i]'] = i
    else:
        D[word_list[i]] += i

Then I get a KeyError for a certain word and I don’t understand why I should be getting an error.

Answer 1

I modified you solution a bit to work

word_list = ['a', 'b', 'c', 'b', 'c', 'a', 'e']
dict = {'a': [], 'b': [], 'c': [], 'e': []}
for i in range(len(word_list)):
    if word_list[i] not in dict:
        dict[word_list[i]] = [i]
    else:
        dict[word_list[i]].append(i)

Result

{'a': [0, 5], 'c': [2, 4], 'b': [1, 3], 'e': [6]}