Angus Rodgers wrote: > Wesley Chun, /Core Python Programming/, Ex. 6-13: > > "[...] An atoc() was never implemented in the string module, so > that is your task here. atoc() takes a single string as input, > a string representation of a complex number [...] and returns > the equivalent complex number object with the given value [...]"
It's true that atoc() was never implemented in the string module, but the builtin complex() does the same thing (and more). > <http://python.pastebin.com/d6f7c679f> (retention: 1 day) > <http://python.pastebin.com/d2ea157ff> (retention: 1 day) > (helper functions for user input) > > The main functions are short enough to post here, I think, but > there are many explanatory and apologetic comments in the first > file above; also, I would welcome (with a grimace!) any comments > as to whether I am developing a cranky or baroque style (as I'm > working very much on my own, apart from whatever feedback I can > get here), and such misdemeanours are more likely to be noticed > in the second (and longer) of the two files above. > > from string import whitespace > > def no_spaces(str): > return ''.join([ch for ch in str if ch not in whitespace]) > > def atoc(num): > """Convert string representation to complex number.""" > num = no_spaces(num) > n = len(num) > if not n: > raise ValueError > # Ignore first character > for i, ch in enumerate(num[1:]): > if ch == 'j': > # Must be end of string, else invalid > if i != n - 2: > raise ValueError > return complex(0.0, float(num[:-1])) > if ch in '+-' and num[i] not in 'eE': > return complex(float(num[:i + 1]), > float(num[i + 1:-1])) > return complex(float(num), 0.0) > Err... what's the question? Are you asking for style checking or the mentioned "bugs" in the comments? === _const_func = lambda c : (lambda x : c) ... def get_val(typ, prompt=None, valid=_const_func(True)): ... I think that is an over-generalisation. It is much simpler to read def get_val(typ, prompt=None, valid=lambda x: True): because other people reading your code might not know what _const_func do (whether it is simply returning a lambda or it does something more complex). === > # A bug in this program is that, by indiscriminately removing all > # > # whitespace before processing, it fails to catch certain errors, > # > # e.g. " - 1 2 " will be passed to float("-12"). Correcting this > # > # bug is likely to make the program considerably more ... complex. You can avoid that bug by not stripping whitespaces. Ignore them inside the loop (put if ch == '': break) and before passing the number to float, compare the number's length before and after the whitespace is stripped. Not really considerably more complex... === > # (It would seem to be more sensible to learn about the regular > # > # expressions module than to complicate this simplistic program.) With regex, you'll just "simply" need something like: >>> import re >>> pat = r'({s})??(?:({f})({s})?)??({f}j)?$' >>> pat = pat.format(f=r'(?:\d*\.?\d*)', s=r'[+-]') >>> >>> print pat ([+-])??(?:((?:\d*\.?\d*))([+-])?)??((?:\d*\.?\d*)j)?$ >>> >>> tests = ['', '10', '+10', '-10', '10.', '+10.', '-10.', '.4', '+.4', '-.4', '10.4', '+10.4', '-10.4', '10j', '+10j', '-10j', '10.j', '+10.j', '-10.j', '.4j', '+.4j', '-.4j', '10.4j', '+10.4j', '-10.4j', '10+10j', '+10+10j', '-10+10j', '10.+10j', '+10.+10j', '-10.+10j', '10.4+10j', '+10.4+10j', '-10.4+10j', '.4+10j', '+.4+10j', '-.4+10j', '10+10.4j', '10.4+10.4j', '+10.4+10.4j', '+10.4-10.4j'] >>> for t in tests: ... print t, re.match(pat, t).groups() ... (None, None, None, None) 10 (None, '10', None, None) +10 ('+', '10', None, None) -10 ('-', '10', None, None) 10. (None, '10.', None, None) +10. ('+', '10.', None, None) -10. ('-', '10.', None, None) .4 (None, '.4', None, None) +.4 ('+', '.4', None, None) -.4 ('-', '.4', None, None) 10.4 (None, '10.4', None, None) +10.4 ('+', '10.4', None, None) -10.4 ('-', '10.4', None, None) 10j (None, None, None, '10j') +10j (None, '', '+', '10j') -10j (None, '', '-', '10j') 10.j (None, None, None, '10.j') +10.j (None, '', '+', '10.j') -10.j (None, '', '-', '10.j') .4j (None, None, None, '.4j') +.4j (None, '', '+', '.4j') -.4j (None, '', '-', '.4j') 10.4j (None, None, None, '10.4j') +10.4j (None, '', '+', '10.4j') -10.4j (None, '', '-', '10.4j') 10+10j (None, '10', '+', '10j') +10+10j ('+', '10', '+', '10j') -10+10j ('-', '10', '+', '10j') 10.+10j (None, '10.', '+', '10j') +10.+10j ('+', '10.', '+', '10j') -10.+10j ('-', '10.', '+', '10j') 10.4+10j (None, '10.4', '+', '10j') +10.4+10j ('+', '10.4', '+', '10j') -10.4+10j ('-', '10.4', '+', '10j') .4+10j (None, '.4', '+', '10j') +.4+10j ('+', '.4', '+', '10j') -.4+10j ('-', '.4', '+', '10j') 10+10.4j (None, '10', '+', '10.4j') 10.4+10.4j (None, '10.4', '+', '10.4j') +10.4+10.4j ('+', '10.4', '+', '10.4j') +10.4-10.4j ('+', '10.4', '-', '10.4j') >>> >>> # might have just used complex() === _______________________________________________ Tutor maillist - Tutor@python.org http://mail.python.org/mailman/listinfo/tutor
