Python tuple vs generator

Parentheses are used for three different things: grouping, tuple literals, and function calls. Compare (1 + 2) (an integer) and (1, 2) (a tuple). In the generator assignment, the parentheses are for grouping; in the tuple assignment, the parentheses are a tuple literal. Parentheses represent a tuple literal when they contain a comma and are not used for a function call.

You can imagine tuples as being created when you hardcode the values, while generators are created where you provide a way to create the objects.

This works since there is no way (1,2,3,4) could be a generator. There is nothing to generate there, you just specified all the elements, not a rule to obtain them.

In order for your generator to be a tuple, the expression (i for i in sample_list) would have to be a tuple comprehension. There is no way to have tuple comprehensions, since comprehensions require a mutable data type.

Thus, the syntax for what should have been a tuple comprehension has been reused for generators.