iterating over a tuple containing one string actually iterates over characters

Question

I've noticed a weird behavior when iterating over a tuple containing only 1 string:

foo = ("hello")
for entry in foo:
    print(entry)

outputs:

h
e
l
l
o

But I expect here to iterate only once, and output "hello" in a row.

If my tupple contains 2 entries, that's what happening:

foo = ("hello", "world!")
for entry in foo:
    print(entry)

outputs:

hello
world!

Is it a bug in CPython's implementation? Even weirder, this doesn't occur if I use a list instead of a tuple:

foo = ["hello"]
for entry in foo:
    print(entry)

outputs:

hello

`('hello')` **is not** a tuple containing one string. It's just a string. Try `print(type(foo))`. — jonrsharpe, Jun 17 '16 at 14:31
To expand on jonrsharpes comment, the correct way to define a 1 element tuple would be ('hello',) — castis, Jun 17 '16 at 14:32

score 8 · Accepted Answer · answered Jun 17 '16 at 14:33

8

("hello") is not a tuple - it's a string, surrounded with parenthesis, which are meaningless in this context. If you want a single-element tuple, you need a comma after the value:

foo = ("hello",) 
# Here--------^

answered Jun 17 '16 at 14:33

Mureinik

297,002
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306
350

Thanks, sorry for the duplicate question. – Gilles Lourdelet Jun 17 '16 at 14:48

score 1 · Answer 2 · answered Jun 17 '16 at 14:33

1

You have a string not a tuple:

>>> type(('hello'))
<class 'str'>
>>> type(('hello',))
<class 'tuple'>

answered Jun 17 '16 at 14:33

Moses Koledoye

77,341
8
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iterating over a tuple containing one string actually iterates over characters

2 Answers2