python tilde unary operator as negation numpy bool array

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not is implemented through the __nonzero__ special method, which is required to return either True or False, so it can’t give the required result. Instead the ~ operator is used, which is implemented through the __not__ special method. For the same reason, & and | are used in place of and and or.

PEP 335 aimed to allow overloading of boolean operators but was rejected because of excessive overhead (it would e.g. complicate if statements). PEP 225 suggests a general syntax for “elementwise” operators, which would provide a more general solution, but has been deferred. It appears that the current situation, while awkward, is not painful enough to force change.

np.isfinite when called on a scalar returns a value of type np.bool_, not bool. np.bool_ is also the type you get when extracting a scalar value from an array of bool dtype. If you use np.True_ and np.False_ in place of True and False you will get consistent behaviour under ~.

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