Core Python Programming (2nd Edition)

(4, True, 5)
>>> (4, 2) < (3, 5) # tuple comparison
False
In the first example, the less than ( < ) operator took precedence over the comma delimiter intended
for the tuples on each side of the less than sign. The result of the evaluation of 2 < 3 became the second
element of a tuple. Properly enclosing the tuples enables the desired result.
6.18.4. Single-Element Tuples
Ever try to create a tuple with a single element? You tried it with lists, and it worked, but then you tried
and tried with tuples, but you cannot seem to do it.
>>> ['abc']
['abc']
>>> type(['abc']) # a list
>>>
>>> ('xyz')
'xyz'
>>> type(('xyz')) # a string, not a tuple
It probably does not help your case that the parentheses are also overloaded as the expression grouping
operator. Parentheses around a single element take on that binding role rather than serving as a
delimiter for tuples. The workaround is to place a trailing comma (,) after the first element to indicate
that this is a tuple and not a grouping.
>>> ('xyz',)
('xyz',)
6.18.5. Dictionary Keys
Immutable objects have values that cannot be changed. That means that they will always hash to the
same value. That is the requirement for an object being a valid dictionary key. As we will find out in the
next chapter, keys must be hashable objects, and tuples meet that criteria. Lists are not eligible.
Core Note: Lists versus Tuples