Question

In the case of a single element tuple, the trailing comma is required.

a = ('foo',)

What about a tuple with multiple elements? It seems that whether the trailing comma exists or not, they are both valid. Is this correct? Having a trailing comma is easier for editing in my opinion. Is that a bad coding style?

a = ('foo1', 'foo2')
b = ('foo1', 'foo2',)

Answer 1

In all cases except the empty tuple the comma is the important thing. Parentheses are only required when required for other syntactic reasons: to distinguish a tuple from a set of function arguments, operator precedence, or to allow line breaks.

The trailing comma for tuples, lists, or function arguments is good style especially when you have a long initialisation that is split over multiple lines. If you always include a trailing comma then you won’t add another line to the end expecting to add another element and instead just creating a valid expression:

a = [
   "a",
   "b"
   "c"
]

Assuming that started as a 2 element list that was later extended it has gone wrong in a perhaps not immediately obvious way. Always include the trailing comma and you avoid that trap.