'''
    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(f'Usage: {sys.argv[0]} filename\n', 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(f'Here is the error message built into the exception:\n  {e}\n', file=sys.stderr)
    exit()

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

open_file.close()

print()

print('============== reading from a file using the "with" statement ==============')
print('  (this ensures that your file will get closed automatically)')
with open(file_name) as open_file:
    for line in open_file:
        line = line.upper()
        print(line, end='')
print()
        
print('=============== writing to a file named output1.txt ==============')
try:
    open_file = open('output1.txt', 'w')
except Exception as e:
    print(f'Here is the error message built into the exception:\n  {e}\n', file=sys.stderr)
    exit()

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

print()

print('=============== writing to a file named output2.txt using "with" ==============')
print('  (this is a more modern and robust idiom for opening and using files)')
with open('output2.txt', 'w') as open_file:
    print('the moose frolicked', file=open_file)
    print('in the meadow', file=open_file)

print()