The first is not a tuple, that's just a single integer, grouped by parentheses (and since there is no other expression here the parentheses are ignored). It is the **comma** that makes something a tuple (except for the empty tuple `()`)`. Parentheses are optional unless the commas could be interpreted as part of other, surrounding syntax (such as a call).
– Martijn PietersJun 07 '16 at 20:30