I'm trying to figure out why the following code transforms ascii STX (control-b) into "\x82". The perl module I use returns a value of "^B", and that is also what the application I am communicating with expects to see. Some ascii characters such as FS and GS come through fine, but STX and ETX get transformed incorrectly (at least for what I need they do).
What am I missing here? Chris > But here's one for you anyway. It raises an exception if any > input character is non-ASCII, otherwise when you call set_parity() > with a string and a parity parameter of 'even', 'mark', 'none', > 'odd', or 'space', it returns a string of the same length with > the high (parity) bits set appropriately. > > '''parity module for python''' > # Copyright 2005 Engenuity Corporation > # Released under the "MIT license" > # at http://www.opensource.org/licenses/mit-license.php > > import string > import operator > > def _makeTable(parity): > bitMap = {'even': [0,128], 'odd': [128,0], 'mark': [128,128]} > table = [] > for c in range(128): > even_odd = (sum(bool(c & 1<<b) for b in range(8))) & 1 > cp = chr(c | bitMap.get(parity, [0,0])[even_odd]) > table.append(cp) > table.extend(chr(c) for c in range(128, 256)) > table = ''.join(table) > return table, table[128:] > > _map = {} > for parity in 'even odd mark space none'.split(): > _map[parity] = _makeTable(parity) > > def set_parity(data, parity='none'): > '''return string with parity bits, accepting only ASCII characters > (0..127) as input''' > out = string.translate(data, *_map[parity.lower()]) > if len(out) != len(data): > raise ValueError('non-ASCII characters in input') > else: > return out > > if __name__ == '__main__': > print 'Running self-tests for parity.py' > > # check for invalid input handling > for input in [ '\xff', '\x80', 'test\xA0ing' ]: > try: > set_parity(input) > except ValueError: > pass > else: > assert False, 'no exception for non-ASCII input' > > # check for various valid inputs > for i, (parity, input, expected) in enumerate([ > ('space', 'test', 'test'), > ('SPACE', '\x00\x7f', '\x00\x7f'), > ('mark', 'test', '\xf4\xe5\xf3\xf4'), > ('Odd', '\x00test\x7f', '\x80\xf4\xe5s\xf4\x7f'), > ('even', '\x00\x01\x02\x03test\x7d\x7e\x7f', > '\x00\x81\x82\x03te\xf3t\x7d\x7e\xff'), > ]): > actual = set_parity(input, parity) > assert expected == actual, 'case %d: %r != %r' % (i, expected, actual) > > print 'All tests passed.' > -- > http://mail.python.org/mailman/listinfo/python-list > -- http://mail.python.org/mailman/listinfo/python-list
