On 10/9/10 10:30 PM, John Nagle wrote: > Python protects global variables from similar confusion > by making them read-only when referenced from an inner scope > without a "global" statement.
No. It doesn't. Assignments simply always apply to local variables, unless you explicitly indicate otherwise. There is no "protection" going on here. Its the exact same principle of what's going on with classes/instances; assignment to an instance always apply to variables local to that instance-- and not global to the class-- unless you explicitly indicate otherwise. There is no protection of the global going on: in all cases, you can create a new local variable that shadows the global that was previously there. The syntax is just different. For regular, free variables, you "explicitly indicate otherwise" by using the global statement. For class/instance variables, you "explicitly indicate otherwise" by doing class.var or self.__class__.var = whatever. Yes, the behavior of "get" and "set" are distinctly different. "get" in all cases -- both free variables in functions, and when getting attributes from your instance -- looks up the tree, starting at your most local namespace and walking up until it finds what you want. For free variables, this is a short list: locals(), enclosing nested function scopes, globals(), builtins. For attributes, it starts on your instance, then goes to the class, then up the superclass tree. The "sets" in all cases don't walk up the tree at all. They only set in the most local namespace, unless again, you explicitly tell it to do something else. Sure, this means you can accidentally shadow a global and run into problems. It also means you can forget that "explicitly tell it" and run into other problems. But its still a feature, and basically part of the core, fundamental object model of Python. -- Stephen Hansen ... Also: Ixokai ... Mail: me+list/python (AT) ixokai (DOT) io ... Blog: http://meh.ixokai.io/
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