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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:

fruit = "banana" print(len(fruit))

11-9-2: What is printed by the following statements?

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.

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To get the last letter of a string, you might be tempted to try something like this:

fruit = "banana" length = len(fruit) last = fruit[length]

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:

fruit = 'banana' length = len(fruit) last = fruit[length-1] print(last)

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.

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.

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.

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