Section 8.5 Length
The
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.
Check your understanding
Checkpoint 8.5.2.
Checkpoint 8.5.3.
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