Letter at a Time

Did you know that using a for loop, you can examine a string one letter at a time? You can use range and tell it how long the string is.

  • len() returns an int representing the total number of characters in the String (including punctuation and whitespace). For example, if the variable str contains the String "hello", then len(str) will return 5.

  • You can access single characters in the string by using square-bracket notation. my_string[n] returns the nth character in the String. The character positions are zero-based. If the variable my_string contains the String "ligature", then my_string[0] (my_string at index 0) will return 'l', and my_string[4] (my_string at index 4) will return 't'.

Files Needed

Save the file as: letter_at_a_time.py

What You Should See

What is your message? Are you ready for this?

Your message is 23 characters long.
The first character is at index 0 and is 'A'.
The last character is at index 22 and is '?'.

Here are all the characters, one at a time:

    0 - 'A'
    1 - 'r'
    2 - 'e'
    3 - ' '
    4 - 'y'
    5 - 'o'
    6 - 'u'
    7 - ' '
    8 - 'r'
    9 - 'e'
    10 - 'a'
    11 - 'd'
    12 - 'y'
    13 - ' '
    14 - 'f'
    15 - 'o'
    16 - 'r'
    17 - ' '
    18 - 't'
    19 - 'h'
    20 - 'i'
    21 - 's'
    22 - '?'

Your message contains the letter 'a' 2 times.

What You Should Do on Your Own

Assignments turned in without these things will receive half credit or less.

  1. If you print range(7), what do you see? What happens if you convert the range to a list and then print that out? E.g., list(range(7))

  2. The for loop is defined so that the loop variable i iterates through the entire range object range(len(message)). If the message was "Hello" what number would be sent to the range function? What numbers would be included within that range object? List them out.

  3. If a string variable contains the value "box", what is its length? What is the index (position) of the last character (the 'x')?

  4. Currently the code prints out the number of ‘a’s in the message. Change it so that it instead prints out the number of vowels (a A e E i I o O u U).

©2021 Daniel Gallo

This assignment is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 United States License.

Creative Commons License

Adapted for Python from Graham Mitchell’s Programming By Doing