# Exercise 4.5, extension of code from 4.2
import sys

try:
    F = float(sys.argv[1])
except IndexError:
    print("You must give a command line argument")
    sys.exit(1)
except ValueError:
    print("The command line argument must be a number")
    sys.exit(1)


C = 5.0/9 * (F-32)
print('Temperature (Celcius): %g' % C)

"""
Terminal> python f2c_cml.py 
You must give a command line argument
Terminal> python f2c_cml.py 7t
The command line argument must be a number
Terminal> python f2c_cml.py 4.5
Temperature (Celcius): -15.2778
"""