Python BMI Utility

bmi.py

#!/usr/bin/env python

def invalid(msg):
    print msg
    exit()

def getFloat(prompt):
    print prompt + ":",
    input = raw_input()
    if len(input) > 0:
        val = float(input)
    else:
        invalid("you entered nothing, nihilist")
    return val

def getRating(bmi):
  rating = ""
  if bmi < 18.5:
      rating = "underweight"
  elif bmi < 25:
      rating = "normal"
  elif bmi < 30:
      rating = "overweight"
  else:
      rating = "obese"
  return rating

weight = getFloat("please enter weight (lbs)")
height = getFloat("please enter height (inches)")
desired_bmi = getFloat("please enter desired bmi")

current_bmi = weight / (height ** 2) * 703
current_rating = getRating(current_bmi)

desired_weight = (desired_bmi * height ** 2) / 703
desired_rating = getRating(desired_bmi)

print "you are %0.1f inches tall and weigh %0.1f lbs" \
    % (height, weight)
print "your bmi is currently %0.3f which is considered: %s" \
    % (current_bmi, current_rating.upper())
print "your desired bmi is %0.3f which is considered: %s" \
    % (desired_bmi, desired_rating.upper())
print "to do that, you will need to weigh %0.1f lbs" % desired_weight
print "which is a change of %0.1f lbs" % (desired_weight - weight)