> For the complete documentation index, see [llms.txt](https://mrparkonline.gitbook.io/guide-to-high-school-computer-science/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://mrparkonline.gitbook.io/guide-to-high-school-computer-science/python-programming/python-programming/collections/strings/string-indexing.md). # String Indexing In Python, we can access a certain/individual item in a sequence if the data type is **indexable**. To index/access a single item from a string, we use **\[ ] square brackets**. ```python # Example ''' Looking at: 'Hello!' | H | e | l | l | o | ! | 0 1 2 3 4 5 6 ''' word = 'Hello!' print('word[2]:', word[2]) print('word[1]:', word[1]) print('word[0]:', word[0]) print('word[5]:', word[5]) print('word[6]:', word[6]) ``` ``` word[2]: l word[1]: e word[0]: H word[5]: ! --------------------------------------------------------------------------- IndexError Traceback (most recent call last) in 14 print('word[0]:', word[0]) 15 print('word[5]:', word[5]) ---> 16 print('word[6]:', word[6]) IndexError: string index out of range ``` **NOTE:** * Indexing always **starts at 0 (zero)** * Indexing always accesses a single item from the sequence, for strings: **a character from the targetted string** * The index value *cannot go beyond the limit of the sequence*. Mathematically, the index value cannot be greater than length of the sequence subtracted by one. * Examine the error for `print('word[6]:', word[6])`: gives us index out of range error ``` Looking at: 'Hello!' | H | e | l | l | o | ! | 0 1 2 3 4 5 6 ``` * Notice that our index value in this diagram starts at the **left of the item** * When we index, it will go to the given location and look at the item to the right of the index * Therefore, `print('word[1]:', word[1])` gives us: `e` #### Negative Indexing Just like how we can use positive integer-indexes to access values, we can also use negative integer-indexes to access values as well. ```python # Example ''' Looking at: 'Hello!' | H | e | l | l | o | ! | H | e | l | l | o | ! | -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 ''' word = 'Hello!' print('word[-1]:', word[-1]) print('word[-3]:', word[-3]) print('word[-5]:', word[-5]) print('word[-6]:', word[-6]) print('word[-7]:', word[-7]) ``` ``` word[-1]: ! word[-3]: l word[-5]: e word[-6]: H --------------------------------------------------------------------------- IndexError Traceback (most recent call last) in 14 print('word[-5]:', word[-5]) 15 print('word[-6]:', word[-6]) ---> 16 print('word[-7]:', word[-7]) IndexError: string index out of range ``` **NOTE:** * Index of `-1` is the quickest way to grab the last value of an indexable sequence * Examine that at -6 and 0 we got the value of `H` for `Hello!`, they are located at the same place ``` Looking at: 'Hello!' | H | e | l | l | o | ! -6 -5 -4 -3 -2 -1 ``` * Much like how we look at the right of positive indexes, we do the same for negative indexes * The indexes are laid out like an integer line with the string itself duplicated; however, Python does not actually create the string as a double * It is **smart enough** to know how to handle positive and negative indexes with a single instance of the sequence