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2 September, 2015 - 17:48

What does the following function do?

def find(word, letter):
    index = 0
    while index < len(word):
        if word[index] == letter:
          return index
        index = index + 1
    return -1

In a sense, find is the opposite of the [] operator. Instead of taking an index and extracting the corresponding character, it takes a character and finds the index where that character appears. If the character is not found, the function returns -1.

This is the first example we have seen of a return statement inside a loop. If word[index] == letter, the function breaks out of the loop and returns immediately.

If the character doesn’t appear in the string, the program exits the loop normally and returns -1.

This pattern of computation—traversing a sequence and returning when we find what we are looking for—is called a search.

Exercise 8.4.Modify findso that it has a third parameter, the index in wordwhere it should start looking.