Chapter 8. Strings
A String Is a Sequence
A string is a sequence of characters. You can access the characters one at a time with the bracket operator:
>>> fruit = 'banana' >>> letter = fruit
The second statement selects character number 1 from
fruit and assigns it to
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
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 >>> print letter b
b is the 0th letter
the 1th letter (“one-eth”), and
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
len is a built-in
function that returns the number of characters in a string:
>>> fruit = 'banana' >>> len(fruit) 6
To get the last letter of a string, you might be tempted to try something like this:
>>> length = len(fruit) >>> last = fruit[length] IndexError: string index out of range
The reason for the
is that there is no letter in
’banana’ with the index 6. Since we started counting at zero, the six letters are numbered 0 to 5. To get the last character, you have to subtract ...