Appending list(element) to another list gives an element by letter

Question

Sorry for this question, but I do not understand why the difference between the following results when adding an element to the list as a list itself to other list:

list_a=[]
list_b=['HELLO','WORLD']
for word in list_b:
    list_a.append([word])
print("Append to dist_list single word: ", list_a)

Output: Append to list_a:  [['HELLO'], ['WORLD']]

list_a=[]
list_b=['HELLO','WORLD']
for word in list_b:
    list_a.append(list(word))
print("Append to list_a: ", list_a)

output: Append to list_a:  [['H', 'E', 'L', 'L', 'O'], ['W', 'O', 'R', 'L', 'D']]

There are no spaces in this result. The difference is that `list(word)` and `[word]` do not mean the same thing. — kaya3, Dec 05 '19 at 17:46
`list()` accepts iterator, in the case of `list('HELLO')` you will get list of separate characters. In the case of `['HELLO']` you will get list containing one string. — Andrej Kesely, Dec 05 '19 at 17:46
Yes. Why are you doing this? Why not just `list_a.append(word)`? — Daniel Roseman, Dec 05 '19 at 17:46
Sorry, I stated the title wrongly, each letter becomes an element in the list instead of the whole word would become an element. I am doing this because I have a process after that takes a list of lists. Usually, the result would be `[['Hello','world'],['Hola','mundo']]`, but sometimes I will get just `[['Hello','World']]` like in the example. I am adding to another list to fulfill requirements of the following process. — John Barton, Dec 05 '19 at 17:52

score 1 · Accepted Answer · answered Dec 05 '19 at 17:48

When you perform list() to a string, the string gets turned into a list that's separated for each individual value. For example:

a = 'string'
b = list(a) 
b = ['s','t','r','i','n','g']

Therefore the difference comes because in the first case you are appending two items (both being strings) and in the second one, you are appending the string previously turned into a list with the logic explained above, hence you've appended a list for each string. This is the differnece in the results you are getting. First case add two strings, second case add two lists.

Appending list(element) to another list gives an element by letter

1 Answers1