Exceptions can be used to indicate problems that occur when an object is being con- structed. Write a Python program that shows a constructor passing information about constructor fail- ure to an exception handler that occurs after a try statement. The exception raised also should contain the arguments sent to the constructor.

Question

What will be an ideal response?

Answer 1

```
# Raising exceptions in constructors.

class MonthError( StandardError ):
"""Error with month instance"""
pass

class Month:
"""Represent month as a string"""

months = { 1 : "January",
2 : "February",
3 : "March",
4 : "April",
5 : "May",
6 : "June",
7 : "July",
8 : "August",
9 : "September",
10 : "October",
11 : "November",
12 : "December" }

def __init__( self, monthNumber ):
"""Month constructor; accept integer argument"""

# attempt to assign value to monthString instance
try:
self.monthString = self.months[ monthNumber ]
except KeyError:
raise MonthError, \
"Invalid month value (%d)--see Month.months" \
% monthNumber

def __str__( self ):
"""String representation of Month"""

return self.monthString

# main program

# continually prompt user until they enter integer value
# in range [1, 12]
while 1:

# get integer value from user
try:
userInteger = int(
raw_input( "\nEnter integer for month: " ) )
monthName = str( Month( userInteger ) )
break

# if user did not enter integer
except ValueError:
print "Must enter integer value!"

# if integer not in range [1, 12]
except MonthError, exception:
print exception

print "The month name is", monthName
```
Enter integer for month: 0
Invalid month value (0)--see Month.months
Enter integer for month: a
Must enter integer value!
Enter integer for month: 12
The month name is December