Terry J. Reedy <tjre...@udel.edu> added the comment:
For rich comparisons, a proper explanation is given in the rich comparison entry in the datamodel section ( #41910) "A rich comparison method may return the singleton NotImplemented if it does not implement the operation for a given pair of arguments. By convention, False and True are returned for a successful comparison. However, these methods can return any value, so if the comparison operator is used in a Boolean context (e.g., in the condition of an if statement), Python will call bool() on the value to determine if the result is true or false." bool(x) calls x.__bool__ and requires that the latter return False or True. As for the other two comparisons, x is y always returns False or True for a proper implementation because int == int always does. If y.__contains__(x) does not raise, x in y returns bool(y.__contains__(x)), clamping aberrant implementations of __contains__. A replacement text might be "Comparisons normally yield boolean values: True or False. But rich comparisons not in a Boolean context may yield anything." Possibly link 'rich comparisons' to the datamodel section. ---------- nosy: +terry.reedy _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue41911> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
