Question

Just came across this little bit of weirdness in Python and thought I’d document it write it as a question here in case anyone else is trying to find an answer with the same fruitless search terms I was

Looks like tuple unpacking makes it so you can’t return a tuple of length 1 if you’re expecting to iterate over the return value. Although it seems that looks are deceiving. See the answers.

>>> def returns_list_of_one(a):
...     return [a]
...
>>> def returns_tuple_of_one(a):
...     return (a)
...
>>> def returns_tuple_of_two(a):
...     return (a, a)
...
>>> for n in returns_list_of_one(10):
...    print n
...
10
>>> for n in returns_tuple_of_two(10):
...     print n
...
10
10
>>> for n in returns_tuple_of_one(10):
...     print n
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'int' object is not iterable
>>>

Answer 1

You need to explicitly make it a tuple (see the official tutorial):

def returns_tuple_of_one(a):
    return (a, )