pr01 "binary"

pr01.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys
from collections import deque
from pr01 import prefixParser

USAGE_MESSAGE = "pr01 [file]"
EXTENDED_MESSAGE = '''
Takes a file as an argument or on stdin, parses it as an expression tree, and
evaluates the result.

Options
    -h, --help                          print this message
'''


def log(*msgs):
    '''log messages to stderr'''
    for msg in msgs:
        print >>sys.stderr, msg,
    print >>sys.stderr
    sys.stderr.flush()

def usage(code=None):
    '''Prints the usage and exits with an error code specified by code. If code
    is not given it exits with error_codes['usage']'''
    log(USAGE_MESSAGE)
    if code is None:
        log(EXTENDED_MESSAGE)
        code = 1
    sys.exit(code)

def main(argv):
    try:
        # First we get the values from the file.  We don't need the children
        # number, but we check that it's appropriate in split_line().
        with sys.stdin as file_in:
            # Strip empty lines from the file
            file_lines = [l for l in (line.strip() for line in file_in) if l]
        # Split them into tuples (children count, value)
        tuple_list = [prefixParser.split_line(line) for line in file_lines]
        # Extract value tuples, discarding the children count
        value_list = [value for _, value in tuple_list]
        # Finally, we parse the lists into a mathematical expression, evaluate
        # it, and print the result.
        print prefixParser.parse(deque(value_list))
    except ValueError, e:
        # Any ValueErrors raised during this process indicate failure at one
        # step or another, and contain suitable error messages.
        log(str(e))
        sys.exit(1)
    except Exception, e:
        # If we get any other kind of exception, we had some serious error.
        # We'll just report the exception string and hope it's informative.
        log(str(e))
        sys.exit(1)
    finally:
        # If we make it here, we're done and can exit successfully.
        sys.exit(0)


if __name__ == "__main__":
    main(sys.argv[1:])