"""
Exercise 4.5 from "A primer on...".
Extend the program from Ex. 4.2 to handle errors
caused by missing or wrong input. The exercise only 
asks us to handle IndexError (missing argument), but 
we extended it to also handle ValueError (wrong format). 
"""
import sys

try:
    F = sys.argv[1]
    F = float(F)
except IndexError:
    print('Det mangler et kommandolinjeargument')
    exit()
except ValueError:
    print('Feil format på kommandolinjeargument')
    exit()

C = (F - 32) * 5 / 9
print(C)

"""
Terminal> python f2c_cml_exc.py 
Det mangler et kommandolinjeargument
Terminal> python f2c_cml_exc.py 56f
Feil format på kommandolinjeargument
Terminal> f2c_cml_exc.py 56
13.333333333333334
"""