Section 7.2 Getting the length of a string using len()
len() is a built-in function that returns the number of characters in a string:
Checkpoint 7.2.1.
street = "125 Main Street"
print(len(street))
13
Incorrect! Don't forget to include the spaces in the count. Try again.
15
Correct! The len function returns the number of characters in the string, including spaces.
10
Incorrect! This would be true if the len function only returned the number of different characters present, but it includes all characters, including spaces. Try again.
6
Incorrect! This is the length of the word "street", not the length of the string named street. Try again.
To get the last letter of a string, you might be tempted to try something like this:
The reason for the IndexError is that there is no letter in “banana” with the index 6. Since we started counting at zero, the six letters are numbered 0 to 5. To get the last character, you have to subtract 1 from length:
Alternatively, you 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.
Checkpoint 7.2.2.
11-9-5: What is printed by the following statements?
s = "green apples"
print(s[len(s)-5])
l
Incorrect! Take a look at the index calculation again. Try again.
p
Correct! Yes, len(s) is 12 and 12-5 is 7. Index 7 of s is 'l'.
a
Incorrect! 'a' is at index 6. Try again.
Error, len(s) is 12 and there is no index 12.
Incorrect! You subtract 5 before using the index operator, so there isn't an error. Try again.
Checkpoint 7.2.3.
11-9-6: What is printed by the following statements?
s = "python rocks"
print(s[-3])
c
Correct! 'c' is three characters from the end of the string.
k
Incorrect! s[-3] means to use the third to last character. Try again.
s
Incorrect! When expressed with a negative index, 's' is at index -1. Try again.
Error, negative indices are illegal.
Incorrect! Python uses negative indices to count backwards from the end. Try again.
