How to extract elements from a list when the list is made of string and list of differents size?

Question

I have a list made of lists and strings, and I want to extract each element from the list. And if the extracted element is a list, extract the elements from the list.

This is just to manipulate the lists a bit so I don't have anything planned with these items once done, so after that puting them in another list is enought.

for example, i have this list :

meal = [
    'salad',
    ['coquillette', 'ratatouille', 'steak'],
    'cheese', ['ice cream', 'tart', 'fruit']
]

and I want :

dishes = [
    'salad',
    'coquillette',
    'ratatouille',
    'steak',
    'cheese',
    'ice cream',
    'tart',
    'fruit'
]

for the moment I have done this :

meal = ['salad', ['coquillette', 'ratatouille', 'steak'], 'cheese', ['ice cream', 'tart', 'fruit']]
dishes = []

for dish in meal:
    for item in dish:
        if isinstance(dish, list):
            dishes.append(item)
            #print(item)
    else:
        dishes.append(dish)
        #print(dish)

print(dishes)

but I get :

[
    'salad',
    'coquillette',
    'ratatouille',
    'steak',
    **['coquillette', 'ratatouille', 'steak']**,
    'cheese',
    'ice cream',
    'tart',
    'fruit',
    **['ice cream', 'tart', 'fruit']**
]

any advices ?

use `dishes.extend(item)` when `item` is a list, and `append` when it's just a string — Anentropic, Jul 07 '22 at 14:46
also your `else:` block needs to be indented by one more level, to be a clause in the `if` check, rather than in the `for` loop — Anentropic, Jul 07 '22 at 14:48

score 1 · Answer 1 · edited Jul 07 '22 at 17:05

1

for i in my_list:
    if type(i) == str:
        other_list.append(i)
    elif type(i) == list:
        for x in i:
            other_list.append(x)

This should work

edited Jul 07 '22 at 17:05

ChrisGPT was on strike

127,765
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answered Jul 07 '22 at 14:46

Awesome Holman

26
1

Welcome to Stack Overflow. Code is a lot more helpful when it is accompanied by an explanation. Stack Overflow is about learning, not providing snippets to blindly copy and paste. Please [edit] your answer and explain how it answers the specific question being asked. See [answer]. – ChrisGPT was on strike Jul 07 '22 at 17:05

score 1 · Accepted Answer · answered Jul 07 '22 at 14:47

You can do something like this:

meal = ['salad', ['coquillette', 'ratatouille', 'steak'], 'cheese', ['ice cream', 'tart', 'fruit']]
out = []
for m in meal:
  out += [m] if not isinstance(m, list) else m
print(out)

['salad', 'coquillette', 'ratatouille', 'steak', 'cheese', 'ice cream', 'tart', 'fruit']

score 1 · Answer 3 · answered Jul 07 '22 at 14:48

1

You were very close:

...
for dish in meal:
    if isinstance(dish, list):
        for item in dish:
            dishes.append(item)
...

answered Jul 07 '22 at 14:48

Scott Hunter

48,888
12
60
101

score 1 · Answer 4 · answered Jul 07 '22 at 14:50

1

meal = ['salad', ['coquillette', 'ratatouille', 'steak'], 'cheese', ['ice cream', 'tart', 'fruit']]
dishes = []

for dish in meal:
    if isinstance(dish, list):
        dishes.extend(dish)
    else:
        dishes.append(dish)

print(dishes)

answered Jul 07 '22 at 14:50

Anentropic

32,188
12
99
147

score 1 · Answer 5 · answered Jul 07 '22 at 14:53

1

My weird one liner :D [ s for tmpL in [[*e] for e in L] for s in tmpL]

Recursive general solution

def flat_rec(l: list):
   for e in l:
      if isinstance(e,str):
         yield e
      elif isinstance(e,list):
         yield flat_rec(e)
      else:
         raise ValueError("Oh no!")

answered Jul 07 '22 at 14:53

Axeltherabbit

680
3
20

The recursive version has the added benefit of working no matter how many levels deep the nesting goes. – Scott Hunter Jul 07 '22 at 14:55
I like it too, would be a better answer if it showed it being applied to OP's code (even though usage is fairly obvious, OP may not have used a generator function before) ... also for one-letter var names `e in l` and the error could be more informative – Anentropic Jul 07 '22 at 15:04

How to extract elements from a list when the list is made of string and list of differents size?

5 Answers5