Logical operators¶

Introduction¶

Conditionals are a nice way to make decisions by asking if something equals True or not. But often one condition is not enough. We may want to take the opposite of our result. Or for instance if we want to make a decision upon turtle.xcor() and turtle.ycor() we have to combine them. This can be done with logical operators.

Negation of a statement¶

If we want something to be False we can use not. It is a logical operator:

x = False
if not x :
    print("condition met")
else:
    print("condition not met")

Exercise¶

The turtle gives us a useful function to know if it is drawing or not: turtle.isdown(). This function returns True if the turtle is drawing. As we have seen earlier, the function turtle.penup() and turtle.pendown() toggle between drawing while moving, or just moving without a trace.

Can we write a function that only goes forward if the pen is up?

Solution¶

def stealthed_forward(distance):
    if not turtle.isdown():
        turtle.forward(distance)

This and that or something else¶

Two easy to understand operators are and and or. They do exactly what they sound like::

if 1 < 2 and 4 > 2:
    print("condition met")

if 1 > 2 and 4 < 10:
    print("condition not met")

if 4 < 10 or 1 < 2:
    print("condition met")

You are not restricted to one logical operator. You can combine as may as you want.

Exercise¶

Earlier we put the turtle in a circular prison. This time let’s make it a box. If the turtle goes more than 100 in the X or Y axis then we turn the turtle back around to the center.

Solution¶

def forward(distance):
    while distance > 0:
        if (turtle.xcor() > 100
            or turtle.xcor() < -100
            or turtle.ycor() > 100
            or turtle.ycor() < -100):
            turtle.setheading(turtle.towards(0,0))
        turtle.forward(1)
        distance = distance - 1