CSC111 Lab 9 2015

--D. Thiebaut (talk) 07:14, 29 March 2015 (EDT)

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Exceptions

preparation

• Create a new program called lab9_1.py, and copy this code to the new Idle window.

# lab9_1.py
# Your name here

# getInput: returns an integer larger
# than 0.  Expected to be robust
def getInput():
   
   while  True:
      x = int( input( "Enter an integer greater than 0: " ) )
      if x <= 0:
         print( "Invalid entry.  Try again!" )
      else:   
         return x

def main():
   num = getInput()
   print( "You have entered", num )

main()

• Test it with numbers such as -3, -10, 0, 5. Verify that the input function works well when you enter numbers.
• Test your program again, and this time enter expressions such as "6.3", or "hello" (without the quotes).
• Make a note of the Error reported by Python:

• Modify your function and add code that will catch the exception:

# betterGetInput: returns an integer larger
# than 0.  Catches Value errors
def betterGetInput():
    
   # repeat forever...
   while  True:

      # try to get an int
      try:
          x = int( input( "Enter an integer greater than 0: " ) )
      except ValueError:
          # the user must have entered something other than an int
          print( "Invalid entry.  Not an integer.  Try again!" )
          continue

      # No errors caught.  See if the number is negative
      if x <= 0:
         print( "You entered a negative number.  Try again!" )
      else:   
         return x