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Engineering LibreTexts

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