write a list to file but error : writelines() argument must be a sequence of strings

Question

I have a list, and I want to write that list to a file txt

lines=[3,5,6]

result = open("result.txt", "w")
result.writelines(lines)
result.close()

But when I run, I get the following error:

writelines() argument must be a sequence of strings

@ozgur, with your solution I can resolve the error. But I get in result file 3 5 6 without newline. How to add newline between the data of the list? — Erna Piantari, Oct 27 '16 at 09:42
@Baris: if you have a string, then just use `file.write(string)`. `file.writelines(string)` will still treat the string as a *sequence*, which I guess will be less efficient. — Eugene Yarmash, Oct 28 '16 at 08:05

score 7 · Answer 1 · answered Oct 27 '16 at 09:39

7

The error is self-explanatory: you must pass a sequence of strings, not numbers to file.writelines(). So convert the numbers to strings, and perhaps add newlines:

lines = [3, 5, 6]
with open("result.txt", "w") as f:
    f.writelines([str(line) + "\n" for line in lines])

answered Oct 27 '16 at 09:39

Eugene Yarmash

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Why keep the brackets in writelines? Even though is it is important to understand that is list comprehension, it is useless in this case. – Kruupös Oct 27 '16 at 09:46
2

Max: both will work, although for small number of items list comprehensions are usually faster than generators. – Eugene Yarmash Oct 27 '16 at 09:59

score 1 · Answer 2 · answered Oct 27 '16 at 09:39

1

Well, you're giving it a list of integers and it plainly told you it wants a sequence of strings.
It'd just be rude not to oblige:

result.writelines(str(line) for line in lines)

answered Oct 27 '16 at 09:39

tzaman

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write a list to file but error : writelines() argument must be a sequence of strings

2 Answers2