Returning tuple with a single item from a function

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

Answer 1

This is not a bug, a one-tuple is constructed by val, or (val,). It is the comma and not the parentheses that define the tuple in python syntax.

Your function is actually returning a itself, which is of course not iterable.

To quote sequence and tuple docs:

A special problem is the construction of tuples containing 0 or 1 items: the syntax has some extra quirks to accommodate these. Empty tuples are constructed by an empty pair of parentheses; a tuple with one item is constructed by following a value with a comma (it is not sufficient to enclose a single value in parentheses). Ugly, but effective.

Answer 2

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

def returns_tuple_of_one(a):
    return (a, )

Answer 3

Instead of that ugly comma, you can use the tuple() built-in method.

def returns_tuple_of_one(a):
    return tuple(a)

Answer 4

(a) is not a single element tuple, it's just a parenthesized expression. Use (a,).