Problem when concatenating lists to string with newline

Question

I would like to concatenate 2 lists with new line.

list1 = [1,2]
list2 = [3,4,5]

The expected output format is:

1,2
3,4,5

My code is:

final = []
final.append(list1)
final.append(list2)

final = '\n'.join([str(i) for i in finallist])

But it returns:

'[1, 2]\n[4, 5, 6]'

Because I am going to save this output to txt file, so it has to be a string and print() does not work here. Could anyone advise how can I solve this problem? Thank you very much!

When you call str() on an entire list, you get [ ] in the result. It sounds like you want to call str() on the contents of the list, not the list itself. — John Gordon
– John Gordon, Commented Oct 30, 2020 at 0:34
@JohnGordon apparently no. calling str() on a list makes the whole thing a string — Matiiss
– Matiiss, Commented Oct 30, 2020 at 0:37
@Matiiss I'm not sure what you're saying "no" to? Calling str() on a list certainly does include [ ] in the output string... — John Gordon
– John Gordon, Commented Oct 30, 2020 at 0:42
@JohnGordon in that case I misinterpreted your statement of getting [] as I thought it meant an empty list but even if you get [] in the string too you can .replace() them — Matiiss
– Matiiss, Commented Oct 30, 2020 at 0:44

Matiiss · Accepted Answer · 2020-10-30 00:42:31Z

1

does this fix your issue (its your expected output):

list1 = [1,2]
list2 = [3,4,5]

final = [list1, list2]

final = '\n'.join([str(i).replace('[', '').replace(']', '') for i in final])
with open('yourfile.txt', 'w') as file:
    file.write(final)

edited Oct 30, 2020 at 0:42

answered Oct 30, 2020 at 0:36

Matiiss

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3 Comments

user14504696 Over a year ago

Because I am going to save this output to txt file, so it has to be a string and print() does not work here.

Matiiss Over a year ago

@user14504696 I edited my post is this what you wanted?

user14504696 Over a year ago

Yes, this works. Thank you! I found the result showed in Jupyter notebook still has \n while it is okay when saving to txt file.

Michael · Accepted Answer · 2020-10-30 00:33:23Z

0

Consider the operations here:

final = []  # An empty list
final.append(list1)  # List contains a list: [[1, 2]]
final.append(list2)  # List contains 2 lists: [[1, 2], [3, 4, 5]]

[str(i) for i in finallist]  # Convert each list into a string, put it in a new list
# e.g. This list will contain two values: ['[1, 2]', '[4, 5, 6]']

It sounds like you want to have commas between values in the list, and newlines between lists. Converting the entire list into a string will include the brackets, when you just want to convert each entry into its own string. Like so:

list1 = [str(i) for i in list1]
list2 = [str(i) for i in list2]
final = [list1, list2]
print('\n'.join([','.join(i) for i in final]))

answered Oct 30, 2020 at 0:33

Michael

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3 Comments

user14504696 Over a year ago

Because I am going to save this output to txt file, so it has to be a string and print() does not work here.

Michael Over a year ago

@user14504696 That's okay; just write '\n'.join([','.join(i) for i in final]) to the output file.

user14504696 Over a year ago

Yes, this works. Thank you! I found the result showed in Jupyter notebook still has \n while it is okay when saving to txt file.

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