On Thu, 12 Mar 2015 22:29:24 +1100, Steven D'Aprano <steve+comp.lang.pyt...@pearwood.info> wrote:
> >I would have a loadfile() method which takes a filename on disk, opens the >file and passes the contents (or the open file object) to another method, >load() to do the actual work: > > >class Map: > def __new__(cls, width, height, fill, treasure=None): > # Include additional args as needed. > map = super().__new__.(cls) > map.width = width > map.height = height > map.fill = fill > map.treasure = treasure > return map > > @classmethod > def loadfile(cls, filename): > with open(filename, 'r') as f: > map = cls.load(f) > return map > > @classmethod > def load(cls, f): > # validate and parse file contents > # extract width, height, fill, etc. > map = cls(width, height, fill, treasure) > return map > > >To get an empty map, you pass the load method a file-like object that >contains whatever an empty map data file will contain. That could literally >be an external file, if you so choose, or you could simply read it from a >global constant or even an embedded string/bytes object: > > @classmethod > def new(cls): > """Return a new empty map.""" > emptymap = b"blah blah blah width=100 height=100 fill=1" > f = io.StringIO(emptymap) > return cls.load(f) > > >This, naturally, assumes that your map format is simple enough and small >enough that an empty map can be embedded into your code. If an empty map is >4MB on disk, you probably don't want to do this :-) > >Alternatively, set the default arguments to the __new__ constructor to be >whatever values an empty map uses: > > def __new__(cls, width=100, height=100, fill=1, treasure=None): > ... > > >and now your "create empty map" command just calls Map() with no arguments. > Your solution is excelent! Leveraging the __new__ method is something I wasn't considering. It gracefully deals with the absence of __init__, not forcing me to raise an exception or document the class to warn against its use. Thanks a bunch. -- https://mail.python.org/mailman/listinfo/python-list
