making a list of lists and strings into a flat list

Question

I have the following lista that contains lists and strings:

['IBERDROLA', 'ACCOR\xa0SA', ['ADMIRAL'], ['ADECCO', 'IAG']]

I would like to make it a flat_list with this output:

['IBERDROLA', 'ACCOR\xa0SA', 'ADMIRAL', 'ADECCO', 'IAG']

Probably I might not be using the correct keywords to find the desired answer, buy I only found Making a flat list out of list of lists in Python (with no str like mines) into a flat_list which gives the following output:

flat_list = [item for sublist in lista for item in sublist] 

['I', 'B', 'E', 'R', 'D', 'R', 'O', 'L', 'A', 'A', 'C', 'C', 'O', 'R', '\xa0', 'S', 'A', 'ADMIRAL', 'ADECCO', 'IAG']

score 2 · Answer 1 · answered Oct 24 '18 at 13:38

You can use the isinstance() function to check the type of a list item:

lista = ['IBERDROLA', 'ACCOR\xa0SA', ['ADMIRAL'], ['ADECCO', 'IAG']]
flat_list = []

for item in lista:
    if isinstance(item, list):
        flat_list.extend(item)
    else:
        flat_list.append(item)

score 2 · Accepted Answer · answered Oct 24 '18 at 13:39

2

Assuming your list is stored as variable l, you can use a ternary operator with a test of isinstance as a condition:

[i for s in l for i in (s if isinstance(s, list) else (s,))]

answered Oct 24 '18 at 13:39

blhsing

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Exactly what I wanted to post, but any particular reason why `(s,)` and not `[s]`? – tobias_k Oct 24 '18 at 13:40
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Only because tuples have [slightly less overhead](https://stackoverflow.com/questions/68630/are-tuples-more-efficient-than-lists-in-python) than lists, so unless it's meant to be mutated, I prefer using tuples whenever possible. – blhsing Oct 24 '18 at 13:41
FWIW, this happens to be noticeably slower than a simple loop, perhaps due to the nested generator expression and building tuple objects for each string. – Eugene Yarmash Oct 24 '18 at 13:58

Narendra Lucky · Answer 3 · 2018-10-29T11:57:32.453

0

   lst = ['IBERDROLA', 'ACCOR\xa0SA', ['ADMIRAL'], ['ADECCO', 'IAG']]
   new_lst = reduce(lambda x,y:x+y,[val if isinstance(val,list) else [val] for val in lst])
   print new_lst

   Result : ['IBERDROLA', 'ACCOR\xa0SA', 'ADMIRAL', 'ADECCO', 'IAG']

edited Oct 29 '18 at 11:57

answered Oct 24 '18 at 14:07

Narendra Lucky

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making a list of lists and strings into a flat list

3 Answers3