len function, when applied to a string, returns the number of characters in a string.
To get the last letter of a string, you might be tempted to try something like this:
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.
Typically, a Python programmer would combine lines 2 and 3 from the above example into a single line:
lastch = fruit[len(fruit)-1]
Though, from what you just learned about using negative indices, using
fruit[-1] would be
a more appropriate way to access the last index in a list.
You can still use the
len function to access other predictable indices, like the middle character of a string.
fruit = "grape" midchar = fruit[len(fruit)//2] # the value of midchar is "a"
As with strings, the function
len returns the length of a list (the number of items in the list).
However, since lists can have items which are themselves sequences (e.g., strings),
it important to note that
len only returns the top-most length.
alist is the string
"hello", which has length 5.
Check your understanding
Assign the number of elements in
lst to the variable