21.1: A String Is a Sequence
- Page ID
- 15397
A string is a sequence of characters. You can access the characters one at a time with the bracket operator:
>>> fruit = 'banana' >>> letter = fruit[1]
The second statement selects character number 1 from fruit
and assigns it to letter
.
The expression in brackets is called an index. The index indicates which character in the sequence you want (hence the name).
But you might not get what you expect:
>>> print letter a
For most people, the first letter of 'banana'
is b
, not a
. But for computer scientists, the index is an offset from the beginning of the string, and the offset of the first letter is zero.
>>> letter = fruit[0] >>> print letter b
So b
is the 0th letter (“zero-eth”) of 'banana'
, a
is the 1th letter (“one-eth”), and n
is the 2th (“two-eth”) letter.
You can use any expression, including variables and operators, as an index, but the value of the index has to be an integer. Otherwise you get:
>>> letter = fruit[1.5] TypeError: string indices must be integers, not float