"""
Exer. 4.5 from "A primer on..."
The exercise only asks us to handle the error with missing
command line arguments, but this version also handles
arguments of the wrong format (ValueError).
"""

import sys

try:
    F = float(sys.argv[1])
except IndexError:
    print('Please provide 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} degrees F is {C:.2f} degrees C')


"""
Terminal> python f2c_cml_exc.py 
Please provide a command line argument
Terminal> python f2c_cml_exc.py 56f
The argument must be a pure number
Terminal> python f2c_cml_exc.py 56
56.0 degrees F is 13.33 degrees C
"""