This section continues with the idea of short circuiting using boolean operators introduced in Module 4.
evaluate_and = True and False #returns False
#The statement below returns False, but does not evaluate the last True value.
evaluate_and2 = True and False and True
How would this look in practice?
have_pb = True
have_jelly = True
have_bread = True
have_butter = False
have_mayo = False
#This is a function in Python. You do not have to know what it is or how to write one.
#For the sake of this exercise only, we will be using it to simulate a child asking
#asking for a sandwich.
def child():
return "I want a sandwich"
######
if (have_pb and have_jelly and have_bread):
print("Make a PB and J sandwich")
The statement above will always print because all the variables have true values.
if (have_bread and have_butter and have_mayo):
print("Here is a basic sandwich")
else:
print("I'm sad")
#The statement above will always print I'm sad, because have_butter and have_mayo are
#false values.
However, if we change the above and operator to or, we get the following:
if (have_bread or have_butter or have_mayo):
print("I have bread")
else:
print("I'm sad")
#This will always print I have bread, because there is one true value (have_bread).
print(have_bread or child())
The above expression prints True because the first value is a true value and the expression short circuits and does not evaluate child(). Conversely:
print(have_butter or child())
#This prints "I want a sandwich" because a the operator evaluated until the first true
#statement because have_butter is false.
print(have_pb and have_bread and have_butter and child())
#This prints False because the expression short-circuits and child() is not evaluated.
Let us look at more complex combinations of the and/or operators.
print((have_butter and have_bread) or child())
#This prints "I want a sandwich" because the and statement evaluates to False
#The or statement evaluates to child()
print((have_butter or have_bread or child()) and (have_butter or have_mayo))
#This will evaluate to False because the first expression evaluates to True and
#the second to false because there is no true value. When joined by an and operator,
#it becomes print(True and False), which we know prints False.
If you are still slightly confused, here is a handy cheatsheet!
What would the following statements evaluate to?
def adult():
return "I hate cake"
have_cupcake = True
have_icecream = False
have_cakepop = True
have_soda = False
print(have_cupcake and have_icecream and adult())
print(have_icecream or adult() or have_cupcake())
print((have_cakepop and adult()) or (adult() and have_icecream))
