Chapter 12. Tuples
Tuples Are Immutable
A tuple is a sequence of values. The values can be any type, and they are indexed by integers, so in that respect tuples are a lot like lists. The important difference is that tuples are immutable.
Syntactically, a tuple is a comma-separated list of values:
>>> t = 'a', 'b', 'c', 'd', 'e'
Although it is not necessary, it is common to enclose tuples in parentheses:
>>> t = ('a', 'b', 'c', 'd', 'e')
To create a tuple with a single element, you have to include a final comma:
>>> t1 = 'a', >>> type(t1) <type 'tuple'>
A value in parentheses is not a tuple:
>>> t2 = ('a') >>> type(t2) <type 'str'>
Another way to create a tuple is the built-in function
tuple. With no argument, it creates an empty
>>> t = tuple() >>> print t ()
If the argument is a sequence (string, list or tuple), the result is a tuple with the elements of the sequence:
>>> t = tuple('lupins') >>> print t ('l', 'u', 'p', 'i', 'n', 's')
tuple is the name of a
built-in function, you should avoid using it as a variable name.
Most list operators also work on tuples. The bracket operator indexes an element:
>>> t = ('a', 'b', 'c', 'd', 'e') >>> print t 'a'
And the slice operator selects a range of elements.
>>> print t[1:3] ('b', 'c')
But if you try to modify one of the elements of the tuple, you get an error:
>>> t = 'A' TypeError: object doesn't support item assignment
You can’t modify the elements of a tuple, but you can replace one tuple with another:
>>> t = ('A',) + t[1:] >>> print ...