6.5. 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.
Note that alist[0] is the string "hello", which has length 5.
Check your understanding
- 11
- The blank space counts as a character.
- 12
- Yes, there are 12 characters in the string.
What is printed by the following statements?
s = "python rocks"
print(len(s))
- 4
- len returns the actual number of items in the list, not the maximum index value.
- 5
- Yes, there are 5 items in this list.
What is printed by the following statements?
alist = [3, 67, "cat", 3.14, False]
print(len(alist))
Assign the number of elements in lst to the variable output.
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