I believe it's a matter of choice by BDFL when it comes to bool. These might answer your question: http://mail.python.org/pipermail/python-dev/2002-March/020822.html http://mail.python.org/pipermail/python-dev/2004-February/042537.html
specifically: I thought about this last night, and realized that you shouldn't be allowed to subclass bool at all! A subclass would only be useful when it has instances, but the mere existance of an instance of a subclass of bool would break the invariant that True and False are the only instances of bool! (An instance of a subclass of C is also an instance of C.) I think it's important not to provide a backdoor to create additional bool instances, so I think bool should not be subclassable. as for range, that's not a type but a built in function (do a print range) I would suggest that instead of using introspection you could handle the exception TypeError that is thrown. On 22 February 2013 09:35, Wolfgang Maier < wolfgang.ma...@biologie.uni-freiburg.de> wrote: > Dear all, > I am wondering what the rules are that determine whether a built-in type is > subclassable or not. > As examples, why can you base your classes on int or set, > but not on bool or range? > Also: can you use introspection to find out whether a type is valid as a > base type? > Thanks for your help! > > > -- > http://mail.python.org/mailman/listinfo/python-list > -- ./Sven
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