#Exercise 4.5 from A Primer on...
import sys

try:
    F = float(sys.argv[1])   # read 1st command-line argument
except IndexError:
    print("You forgot to add a command line argument!")
    exit()
except ValueError:
    print("The argument must be a pure number.")
    exit()

C = (F-32)*5.0/9
print(f'{F:.1f} degrees Fahrenheit is {C:.1f} degrees Celsius')


"""
Terminal> python f2c_cml_exc.py
You forgot to add a command line argument!
Terminal> python f2c_cml_exc.py 10C
The argument must be a pure number.
Terminal> python f2c_cml_exc.py 45
45.0 degrees Fahrenheit is 7.2 degrees Celsius
"""