9.4. Length¶

The len function, when applied to a string, returns the number of characters in a string.

fruit: str

fruit = "Banana"

print(str(len(fruit)))

​

To get the last letter of a string, you might be tempted to try something like this:

fruit: str

size: int

last: str

​

fruit = "Banana"

size = len(fruit)

last = fruit[size]       # ERROR!

print(last)

​

That won’t work. It causes the runtime error IndexError: string index out of range. The reason is that there is no letter at index position 6 in "Banana". Since we started counting at zero, the six indexes are numbered 0 to 5. To get the last character, we have to subtract 1 from the length. Give it a try in the example above.

fruit: str

size: int

last: str

​

fruit = "Banana"

size = len(fruit)

last = fruit[size - 1]

print(last)

​

Alternatively in Python, we can use negative indices, which count backward from the end of the string. The expression fruit[-1] yields the last letter, fruit[-2] yields the second to last, and so on. Try it! Most other languages do not allow the negative indices, but they are a handy feature of Python!

Check your understanding

s: str
s = "python rocks"
print(str(len(s)))

s: str
s = "python rocks"
print(s[len(s) - 5])

s: str
s = "python rocks"
print(s[-3])