#
#  Demonstrate exceptions with some arithmetic.
#
import math

#
#  Safely read a floating-point value so that it doesn't crash if the user
#  enters something non-numeric.
#
#  Parameters:
#    prompt: The prompt to display before reading the value
#
#  Returns: A floating-point number entered by the user.
#
def safeRead(prompt):
  done = False
  while done == False:
    try:
      a = float(input(prompt))
      done = True
    except ValueError:
      print("That wasn't numeric.  Try again...")

  return a

#
#  Demonstrate the safe read function
#
a = safeRead("Enter the value for a: ")
b = safeRead("Enter the value for b: ")

#
#  Demonstrate the use of other exceptions
#
print(a, "+", b, "=", a+b)
print(a, "-", b, "=", a-b)
print(a, "*", b, "=", a*b)
try:
  print(a, "/", b, "=", a/b)
except ZeroDivisionError:
  # Catch an attempt to divide by 0
  print("Couldn't compute", a, "/", b, "because the denominator is 0.")

try:
  print("log(", a, ") =", math.log(a))
  asdf()  # this function doesn't exist
except ValueError:
  # Catch an attempt to compute log of 0 or negative
  print("Can't compute log of a value less than or equal to zero.")
except:
  # Catch any type of exception (in this case the NameError that occurs
  # when attempting to call a function that doesn't exist)
  print("Opps, something went wrong!")