operate.py

PLUS = ' + '
MINUS = ' - '
MULTIPLY = ' * '
DIVIDE = ' / '

if __name__=='__main__':
	print('Calculator program (\'q\' or \'quit\' to exit):\n')
	while True:
		s = raw_input('Enter operation: ')
		if s=='q' or s=='quit':
			print('Bye!!!')
			exit()
		if s.find(PLUS)>=0:
			l = s.find(PLUS)
			a = float(s[:l])
			b = float(s[l+3:])
			print('Adding {0} and {1}: {2}'.format(a,b,a+b))
		elif s.find(MINUS)>=0:
			l = s.find(MINUS)
			a = float(s[:l])
			b = float(s[l+3:])
			print('Difference of {0} and {1}: {2}'.format(a,b,a-b))
		elif s.find(MULTIPLY)>=0:
			l = s.find(MULTIPLY)
			a = float(s[:l])
			b = float(s[l+3:])
			print('Multiplying {0} and {1}: {2}'.format(a,b,a*b))
		elif s.find(DIVIDE)>=0:
			l = s.find(DIVIDE)
			a = float(s[:l])
			b = float(s[l+3:])
			if b==0.0:
				print('Cannot Divide by Zero.')
				continue
			print('Dividing {0} and {1}: {2}'.format(a,b,a/b))
		else:
			print('Illegal input!!!')