replace multiple strings in a list with a single string by knowing the index

Question

I want to replace multiple strings in a list with a single string by knowing the index. Of course I looked at this question: search for element in list and replace it by multiple items But for my case it is inverse, suppose I have a list as follow:

lst = ['a', 'b1', 'b2', 'b3', 'c']

I know that I have a term:

term = 'b1' + ' b2' + ' b3'

I also know the starting index and the length of that term

lst[1:1+len(term)] = "<term>" + term + "</term>"

I got this result:

['a', '<', 't', 'e', 'r', 'm', '>', 'b', '1', ' ', 'b', '2', ' ', 'b', '3', '<', '/', 't', 'e', 'r', 'm', '>']

However, my expected output:

['a', '<term>b1 b2 b3</term>', 'c']

How can I adjust this to get the desired output?

• 3dSpatialUser: That is because you change a list. But why is your expected output ending with an 'b'? While len(term) is long (it is in fact 8, all the characters). Therefore it will overwrite your whole list.
• Lexpj: Is the last index of your expected output right? 'b'? Shouldn't it be 'c'?
• Erwin: edited the question sorry!

Answer 1

Edit your code such that you insert a list in lst[1:-1]:

lst = ['a', 'b1', 'b2', 'b3', 'c']
term = 'b1' + ' b2' + ' b3'
lst[1:-1] = ["<term>" + term + "</term>"]
print(lst)
>> ['a', '<term>b1 b2 b3</term>', 'c']

As you can see, I also changed the index from lst[1:len(term)+1] to lst[1:-1], such that you keep the first and last terms.

• JL Peyret: Good. But I’d shoot for f"<term>{lst[idx]}+{lst[idx+1] +{lst[idx+2]</term>". With idx at 1. i.e. less hardcoding. But your answer’s still nearly the whole solution.

Answer 2

Using your lst and term list, join the strings into a single string: term_string = "<term>" + " ".join(term) + "</term>"

Then slice to replace the strings with the joined string: lst[1:1+len(term)] = [term_string]

• MB-F: In the question term is a string, but I guess it should be a list as assumed in this answer.
• J. M. Arnold: Ah sorry, read too quickly. Yes, define term as a list to use .join(...): term = ['b1', 'b2', 'b3']!