if len(sys.argv) != 4: # The script name needs to be accounted for as well.
raise RuntimeError("expected 3 command line arguments")
f = open(sys.argv[1], 'rb') # Use first command line argument.
start_line = int(sys.argv[2]) # All arguments come as strings, so need to ...
# The name of the executed script is at the beginning of the argv list.
print('usage:', sys.argv[0], '<filename> <start> <end>')
# You can use it to generate the path prefix of the executed program
# (as opposed to the current module) to access files relative to that,
# which...
# Error messages should not go to standard output, if possible.
print('ERROR: We have no cheese at all.', file=sys.stderr)
try:
f = open('nonexistent-file.xyz', 'rb')
except OSError as e:
print(e, file=sys.stderr)
def main():
if len(sys.argv) != 4 or '--help' in sys.argv[1:]:
print('usage: my_program <arg1> <arg2> <arg3>', file=sys.stderr)
sys.exit(1) # use an exit code to signal the program was unsuccessful
process_data()
