[issue15133] tkinter.BooleanVar.get() behavior and docstring disagree

[Terry J. Reedy]

Terry J. Reedy <tjreedy at udel.edu> added the comment:

Mark: "Variable.get(self) returns self._tk.globalgetvar(self._name). String/Int/Double/Var call str/int/float as appropriate." was meant to say that String/Int/Double/Var.get(self) already call str/int/float on the result of self._tk.globalgetvar(self._name) before returning it. BooleanVar.get does not call bool, but instead calls self._tk.getboolean, which fails to always return a boolean.

Klappnase: I disagree, somehow. bool is a subclass of int, so that False, True are arithmetically indistinguishable from 0, 1. The main difference is on display and 'type(x) = int/bool' comparisons (which should be isinstance()). BooleanVar.get already returns False, True for the tcl boolean values '0', '1' set by tk rather than the user (which I expect should be the usual case for retrieval). So a Python/tkinter program has to be prepared to get proper booleans anyway. Since the purpose of Variables is to synchronize values between user code and tk, TypeVar().set(x).get() should be x when has the proper type. That is now true for everything but bool/Boolean.

I do wonder whether not converting or rejecting bad inputs to .set could cause problems with tk, but maybe some of that is handled later (and silently? if so bad) within _tkinter. I could be persuaded that a behavior fix should only be applied to 3.3.

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<http://bugs.python.org/issue15133>
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