Python comes with some built-in functions for working with strings. One of the most commonly used of these functions is len(). len() returns the number of characters in a string:

favorite_fruit = "blueberry"

length = len(favorite_fruit)

print(length)
# Output: 9

If you are taking the length of a sentence the spaces are counted as well.

fruit_sentence = "I love blueberries"

print(len(fruit_sentence))
# Output: 18

len() comes in handy when we are trying to select characters from the end of a string. What is the index of the last character,"y", of favorite_fruit from above? You can try to run the following code:

last_char = favorite_fruit[len(favorite_fruit)]

print(last_char)

This will result in:

IndexError: string index out of range

Why does this generate an IndexError? Because the indices start at 0, so the final character in favorite_fruit has an index of 8. len(favorite_fruit) returns 9 and, because there is no value at that index, an IndexError occurs.

Instead, the last character in a string has an index that is len(string_name) - 1.

last_char = favorite_fruit[len(favorite_fruit)-1]

print(last_char)
# Output: y

You could also slice the last several characters of a string using len():

length = len(favorite_fruit)
last_chars = favorite_fruit[length-4:]
print(last_chars)
# Output: erry

Using a len() statement as the starting index and omitting the final index lets you slice n characters from the end of a string, where n is the amount you subtract from len().