'''
    files.py -- a few file-related operations, plus a first encounter with exceptions

    Jeff Ondich, 24 October 2006
    Tianna Avery, November 2018, updated for Python 3

    Read, predict the output, experiment.
'''
import sys

print('=============== command-line arguments ==============')
if len(sys.argv) <= 1:
    print('Usage: {0} filename\n'.format(sys.argv[0]), file=sys.stderr)
    exit()

file_name = sys.argv[1]
print('The requested file is', file_name)
print()

print('=============== reading from a file ==============')
try:
    open_file = open(file_name)
except Exception as e:
    print('Here is the error message built into the exception:\n  {0}\n'.format(e), file=sys.stderr)
    exit()

for line in open_file:
    line = line.upper()
    print(line,)

open_file.close()

print()

print('=============== writing to a file ==============')
try:
    open_file = open('output.txt', 'w')
except Exception as e:
    print('Here is the error message built into the exception:\n  {0}\n'.format(e), file=sys.stderr)
    exit()

open_file.write('the moose frolicked\n')
# or, alternatively, print('the moose frolicked\n', file=open_file)
open_file.write('in the meadow\n')
open_file.close()

print()