Lesson 02-02: Specific Letters with String Indexing¶

Length of a String¶

The len() function is a function that will provide the length of a string. The length of a string is basically the number of characters in the string, spaces included. Here are a few quick examples:

print(len("hello!")) # ==> 6

print(len("h e y there")) # ==> 11

name = "Bobert"

print("\n") #ignore this line

print("The name {} has {} characters".format(name,len(name)))

#should print "The name Bobert" has 6 characters"

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6
11


The name Bobert has 6 characters

(ex_strlen_1)

Finding a Specific Letter in a String¶

We can point to a specific character within a string by using string indexing. Every letter, digit, space, or symbol in a string has a position in a string, also known as its index.

We use string indexing to reference a specific character in the string by using its index. The way that this is done is through brackets [] right after the string, with a number inside.

Try to predict what the following code will print:

print("Hello"[4]) #the 4th position of the string

print("Hello"[1]) #the 1st position of the string

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(ex_strindex_1)

Was it what you expected? If this is your first time seeing string indexing, you were probably off by one. That’s because strings use zero-based indexing, which is when the index always starts counting from zero, instead of one.

Here’s an example of the values of word[0], word[3], and word[6] for a variable word = "POKEMON".

It’s worth noting that string indexing gives you a string as the result.

Please keep in mind that from this point on, this book will use 0-based indexing as well. So if you read “the 4th position” or “the 4th letter”, it is the same as saying “the 4th index”

What happens if you reference a position that’s greater than the length of the string itself? Try running the code and see:

word = "POKEMON"

print(word[100])

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(ex_strindex_2)

Trying to reference a position that’s past the end of the string will give you an error! And it even gives us a descriptive error message as well. Use this to your advantage when you come across it.

Typically, to find the last character in a string without knowing what the string is going to be, we would use the expression word[len(word)-1]. But in python, there’s an easier way.

Negative String Indexing¶

You can provide negative numbers as indexes as well. Its behavior is interesting. See the example below:

word = "abcdef"

print(word[-1])

print(word[-2])

print(word[-3])

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(ex_negindex_1)

As you can see, when you provide a negative number, it starts counting from the end, with the last letter having an index of -1. This is very important because this allows us to use string indexing to things like “the second to last letter” of a string.

Checks For Understanding¶

word = "yoloswag"

print("\n")

print() # ==> 'o'

print() # ==> 'a'

print() # the last letter

print() # the 3rd to last letter

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