A tuple is defined in the same way as a list, except that the whole set of elements is enclosed in parentheses instead of
square brackets.
The elements of a tuple have a defined order, just like a list. Tuples indices are zero-based, just like a list, so the first
element of a non-empty tuple is always t[0].
Negative indices count from the end of the tuple, just as with a list.
Slicing works too, just like a list. Note that when you slice a list, you get a new list; when you slice a tuple, you get
a new tuple.
Example 3.16. Tuples Have No Methods
>>> t('a', 'b', 'mpilgrim', 'z', 'example')>>> t.append("new")Traceback (innermost last):
File "<interactive input>", line 1, in ?
AttributeError: 'tuple' object has no attribute 'append'>>> t.remove("z")Traceback (innermost last):
File "<interactive input>", line 1, in ?
AttributeError: 'tuple' object has no attribute 'remove'>>> t.index("example")Traceback (innermost last):
File "<interactive input>", line 1, in ?
AttributeError: 'tuple' object has no attribute 'index'>>> "z"in tTrue
You can't add elements to a tuple. Tuples have no append or extend method.
You can't remove elements from a tuple. Tuples have no remove or pop method.
You can't find elements in a tuple. Tuples have no index method.
You can, however, use in to see if an element exists in the tuple.
So what are tuples good for?
Tuples are faster than lists. If you're defining a constant set of values and all you're ever going to do with it is iterate
through it, use a tuple instead of a list.
It makes your code safer if you “write-protect” data that does not need to be changed. Using a tuple instead of a list is like having an implied assert statement that shows this data is constant, and that special thought (and a specific function) is required to override that.
Remember that I said that dictionary keys can be integers, strings, and “a few other types”? Tuples are one of those types. Tuples can be used as keys in a dictionary, but lists can't be used this way.Actually,
it's more complicated than that. Dictionary keys must be immutable. Tuples themselves are immutable, but if you have a tuple
of lists, that counts as mutable and isn't safe to use as a dictionary key. Only tuples of strings, numbers, or other dictionary-safe
tuples can be used as dictionary keys.
Tuples are used in string formatting, as you'll see shortly.
Tuples can be converted into lists, and vice-versa. The built-in tuple function takes a list and returns a tuple with the same elements, and the list function takes a tuple and returns a list. In effect, tuple freezes a list, and list thaws a tuple.
>>> 
