Why is a tuple of tuples of length 1 not actually a tuple unless I add a comma?

Question

Given a tuple of tuples T:

((\'a\', \'b\'))

and an individual tuple t1:

(\'a\',\'b\')
         


        

Answer 1

Check again. You likely have a bug somewhere else in your code. This check does work.

As for the update, you're not creating a nested tuple.

(('a', 'b')) == ('a', 'b')

If you need a one-element tuple, you need a trailing coma:

(('a', 'b'),)

Answer 2

The problem is because T is not a tuple of tuples, it is just a tuple. The comma makes a tuple, not the parentheses. Should be:

>>> T = (('a','b'),)
>>> t1 = ('a', 'b')
>>> t1 in T
True

In fact, you can loose the outer parentheses:

>>> T = ('a','b'),
>>> t1 = 'a','b'
>>> type(T)
<type 'tuple'>
>>> type(T[0])
<type 'tuple'>
>>> type(t1)
<type 'tuple'>
>>> t1 in T
True

Although sometimes they are needed for precedence, if in doubt put them in. But remember, it is the comma that makes it a tuple.

Answer 3

Doing this (('a', 'b')) does not make a tuple containing a tuple as you can see here:

>>> T = (('a','b'))
>>> T
('a', 'b')

To make a single element tuple you need to add a trialing comma:

>>> T = (('a','b'),)
>>> t1 in T
True
>>> T
(('a', 'b'),)

In fact the parenthesis aren't even a requirement as this will also create a tuple:

>>> t1 = 'a','b'
>>> t1
('a', 'b')
>>> 1,2,3,4,5,6
(1, 2, 3, 4, 5, 6)