Why parenthesis are needed in tuples? [duplicate]

Question

Some time ago I thought that the tuple's constructor was a pair of parentheses ().

Example:

>>> (1, )
(1, )
>>> type((1, ))
<type 'tuple'>
>>> t = (1, )
>>> type(t)
<type 'tuple'>

But now I know that it is the comma ,.

So, doing the same as above:

>>> 1,
(1,)
>>> type(1,)
<type 'int'>  # Why?
>>> 1,2,3
(1,2,3)

But if I do:

>>> type(1,2,3)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: type() argument 1 must be string, not int

This makes sense to me, but:

>>> t = 1,2,3
>>> type(t)
<type 'tuple'>

And finally:

>>> type((1,2,3))
<type 'tuple'>

Here's the question: why are parenthesis needed in the final case if the tuple is just 1,2,3?

Answer 1

In some contexts, commas have another meaning - for example, inside the parentheses of a function call, they separate the parameters. Putting a set of parentheses around your tuple guarantees that it's in a simple expression context, where the commas are interpreted as tuple element separators.