import math
class NegativeNumberError( ArithmeticError ):
pass
def squareRoot( number ):
if number < 0:
raise NegativeNumberError, "Square root of negative number not permitted"
return math.sqrt( number )
while 1:
try:
userValue = float( raw_input( "\nPlease enter a number: " ) )
print squareRoot( userValue )
# float raises ValueError if input is not numerical
except ValueError:
print "The entered value is not a number"
# squareRoot raises NegativeNumberError if number is negative
except NegativeNumberError, exception:
print exception
else:
break
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