Making Choices with if

So far your programs run every line, no matter what. But real programs make decisions: if this, do that, otherwise do something else. Today the turtle learns to choose — and when you mix choices with randomness, things get exciting.

if and else

The shape of a decision in Python:

if something_is_true:
    # do this
else:
    # otherwise do this

Let’s flip a coin. random.random() gives a number between 0 and 1; if it’s under 0.5, go red, otherwise blue. Run it a few times:

 
 
  

Sometimes red, sometimes blue — the turtle decided, based on the coin flip. The lines under if run only when the test is true; the lines under else run only when it’s false.


Try it 🎯


    

  1. Change the two colors to your favorites.
    2. 

  2. Change 0.5 to 0.8 — now it picks the first color much more often. (Higher number = more likely to be true.)
    3. 

  3. Change 0.5 to 0.1 — now the first color is rare.
    4. 



Comparing things


The test can compare numbers, too. == means “is equal to”, > means “greater than”, < means “less than”:


   
   
 
 
 
 
 
  

A big roll draws a big green circle; a small roll draws a small orange one. Run it a few times and watch the roll decide.


Choosing what to draw


A decision can pick the shape, not just the color. Here we randomly choose “circle” or “square” each time through a loop, and if decides which to draw:


   
   
 
 
 
 
 
  

A scattered mix of circles and squares, decided one at a time. Read the if as: “if the random shape came out ‘circle’, draw a circle; otherwise, draw a square.”


More than two choices: elif


Need a third option? elif (short for “else if”) adds another branch:


   
   
 
 
 
 
 
  

Predict it 🔮


In the code above, if pick comes out "green", which lines run? (Just the elif branch — Python checks each test in order and runs the first one that’s true, then skips the rest.)


Fix the bug 🐞


This should draw a big circle when the roll is over 5, but it always draws small. Look at the comparison:


   
   
 
 
 
 
 
  

(The test says roll < 5 (less than), but we want bigger rolls to make the big circle. Change it to roll > 5.)


Your mission 🚀


Make a scatter of three different shapes. Start from the circle/square scatter above, change the choice list to ["circle", "square", "triangle"], and add an elif branch that draws a triangle (3 sides, turn 120).


What you learned today


    

  • if / else let a program choose between paths.
    • 

  • Tests can compare with ==, >, <; elif adds more choices.
    • 

  • Python runs the first matching branch and skips the rest.
    • 

  • Choices + randomness = drawings that surprise you in big ways.
    • 



You now have every tool you need: shapes, loops, variables, functions, randomness, and decisions. Next time is the capstone — you’ll combine them into generative art that’s entirely your own. 🐢
   
 
 
 
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