31: Else and If
In the last exercise you worked out some
if-statements and then tried to guess what they are and how they work. Before you learn more I'll explain what everything is by answering the questions you had from Study Drills. You did the Study Drills right?
- What do you think the
ifdoes to the code under it? An
if-statementcreates what is called a "branch" in the code. It's kind of like those choose your own adventure books where you are asked to turn to one page if you make one choice and another if you go a different direction. The
if-statementtells your script, "If this Boolean expression is True, then run the code under it, otherwise skip it."
- Why does the code under the
ifneed to be indented four spaces? A colon at the end of a line is how you tell Python you are going to create a new "block" of code, and then indenting four spaces tells Python what lines of code are in that block. This is exactly the same thing you did when you made functions in the first half of the book.
- What happens if it isn't indented? If it isn't indented, you will most likely create a Python error. Python expects you to indent something after you end a line with a
- Can you put other boolean expressions from Exercise 28 in the
if-statement? Try it. Yes you can, and they can be as complex as you like, although really complex things generally are bad style.
- What happens if you change the initial values for
dogs? Because you are comparing numbers, if you change the numbers, different
if-statementswill evaluate to
Trueand the blocks of code under them will run. Go back and put different numbers in and see if you can figure out in your head which blocks of code will run.
Compare my answers to your answers, and make sure you really understand the concept of a "block" of code. This is important for when you do the next exercise where you write all the parts of
if-statements that you can use.
Type this one in and make it work too.
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