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Foundations of Python Programming: Functions First

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.
Note that alist[0] is the string "hello", which has length 5.
Check your understanding

Checkpoint 8.5.1.

    What is printed by the following statements?
    s = "python rocks"
  • 11
  • The blank space counts as a character.
  • 12
  • Yes, there are 12 characters in the string.

Checkpoint 8.5.2.

    What is printed by the following statements?
    alist = [3, 67, "cat", 3.14, False]
  • 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.

Checkpoint 8.5.3.

Assign the number of elements in lst to the variable output.
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