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__index and __newindex are the key ones - effectively equivalent to method_missing in Ruby. __index gets called if you try to read a non-existent key, and __new
by sshumaker 15y ago
__index and __newindex are the key ones - effectively equivalent to method_missing in Ruby. __index gets called if you try to read a non-existent key, and __newindex gets called if you try to write to a non-existing key. You can use these methods to implement inheritance, proxies, getters/setters, all sorts of stuff.
- hythloday 15y agoThis sounds very much like Python's __getattribute__ [0] method. Is there a difference I'm not understanding? [0] http://docs.python.org/reference/datamodel.html#object.__getattribute__ http://docs.python.org/reference/datamodel.html#object.__get...
- sshumaker 15y agoI'm not that familiar with Python, but can you use __getattribute__ to provide methods as well? Using __index is the way you typically implement inheritance in Lua.
- timtadh 15y agoyes. >>> class A(object): ... def __getattribute__(self, key): ... try: return object.__getattribute__(self, key) ... except AttributeError: return lambda: 12 ... >>> a = A() >>> a.asdf <function <lambda> at 0x7fbb8fb6f848> >>> a.asdf() 12
- silentbicycle 15y agoYes, but in Python, you set them on every object. In Lua, you can set them once (in a prototype) and have each table share them (and possibly other methods, or a reference to another when lookup fails there). This makes certain behaviors (e.g. implementing your on object system) cheap and straightforward that would be impractical in Python. Imagine if each Python object had one field that stored all the __blah hooks, and objects could share those. It's actually more powerful than that, but it's a good start.