Question

def add(a, b):
    print "ADDING %d + %d" % (a, b)
    return a + b

def subtract(a, b):
    print "SUBTRACTING %d - %d" % (a, b)
    return a - b

def multiply(a, b):
    print "MULTIPLYING %d * %d" % (a, b)
    return a * b

def divide(a, b):
    print "DIVIDING %d / %d" % (a, b)
    return a / b


print "Let's do some math with just functions!"

age = add(30, 5)
height = subtract(78, 4)
weight = multiply(90, 2)
iq = divide(100, 2)

print "Age: %d, Height: %d, Weight: %d, IQ: %d" % (age, height, weight, iq)



print "Here is a puzzle."

# why does the line of code below work in this way?
what = add(age, subtract(height, multiply(weight, divide(iq, 2))))

print "That becomes: ", what, "Can you do it by hand?"

The first thing that the line below the comment does is to call the function divide. I’m curious, why does it do that? Is it because python actually understands the order of operations or is it because of the chain structure that this line has?

Answer 1

Think about it. How would you call add() when you don’t know what the result of subtract() is? How would you call subtract() if you don’t know what the result of multiply() is? Finally, how would you call multiply() if you don’t know what the result of divide() is?

As with algebraic notation, operations inside parentheses get done first. If there are parentheses inside parentheses, the innermost operations are done first. It can’t work any other way.