Add prefix and suffix to each element of a nested list

Question

Suppose I am having a list (which is collection of list of lists), say the list is defined as follows as try_list:

  try_list = [['sun', 'Hello' 'star', 'cluster', 'douglas'], 
              ['age', 'estimate', 'scale', 'moon', 'hi'], 
              ['cosmos', 'mystery', 'system', 'graph']]

I want to add a special character _ or # to each word at the starting and ending point of the list.

For example, the try_list should look like this:

[['_sun_', '_Hello_', '_star_', '_cluster_', '_douglas_'],
 ['_age_', '_estimate_', '_scale_', '_moon_', '_hi_'],
 ['_cosmos_', '_mystery_', '_system_', '_graph_']]

What I have tried is working smoothly for a list, which is shown as follows.

try_list = ['sun', 'Hello' 'star', 'cluster', 'douglas', 'age',  'estimate', 'scale', 'moon', 'hi', 'cosmos', 'mystery', 'system', 'graph']
injected_tokens = []
temp = "_"
with open('try_try.txt', 'w', encoding='utf-8') as d2:
   for word in try_list:
       new_list.append(temp+word+temp)
   d2.write(injected_tokens)

The above code-snippet works perfectly fine for a list not list of lists?

How to achieve the same in list of lists?

Any idea is deeply appreciated!

Thanks!

flatten the list? `flat_list = [x for b in try_list for x in b]` — Patrick Artner, Dec 13 '18 at 19:10
Possible duplicate of [How to make a flat list out of list of lists?](https://stackoverflow.com/questions/952914/how-to-make-a-flat-list-out-of-list-of-lists) — Patrick Artner, Dec 13 '18 at 19:11
@PatrickArtner I think they want to preserve the sub lists in the final result and not flatten the structure. — slider, Dec 13 '18 at 19:13
Thanks Patrick. Actually, I want to write the results in a file without flattening the sub-lists. — M S, Dec 13 '18 at 20:36

yatu · Accepted Answer · 2018-12-13T21:13:35.853

5

You can use a list comprehension:

[[f'_{x}_' for x in i] for i in try_list]

[['_sun_', '_Hello_', '_star_', '_cluster_', '_douglas_'],
 ['_age_', '_estimate_', '_scale_', '_moon_', '_hi_'],
 ['_cosmos_', '_mystery_', '_system_', '_graph_']]

Or using map:

[list(map(lambda x: f'_{x}_', i)) for i in try_list]

edited Dec 13 '18 at 21:13

answered Dec 13 '18 at 19:11

yatu

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Is it time efficient? Does there exists something related to append? – M S Dec 13 '18 at 20:17

Add prefix and suffix to each element of a nested list

1 Answers1