Source code for pennylane.boolean_fn

# Copyright 2018-2021 Xanadu Quantum Technologies Inc.

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# pylint: disable=protected-access
Contains a utility class ``BooleanFn`` that allows logical composition
of functions with boolean output.
import functools

[docs]class BooleanFn: r"""Wrapper for simple callables with boolean output that can be manipulated and combined with bit-wise operators. Args: fn (callable): Function to be wrapped. It must accept a single argument, and must return a boolean. **Example** Consider functions that filter numbers to lie in a certain domain. We may wrap them using ``BooleanFn``: >>> bigger_than_4 = qml.BooleanFn(lambda x: x > 4) >>> smaller_than_10 = qml.BooleanFn(lambda x: x < 10) >>> is_int = qml.BooleanFn(lambda x: isinstance(x, int)) >>> bigger_than_4(5.2) True >>> smaller_than_10(20.1) False >>> is_int(2.3) False These can then be combined into a single callable using boolean operators, such as ``&``, logical and: >>> between_4_and_10 = bigger_than_4 & smaller_than_10 >>> between_4_and_10(-3.2) False >>> between_4_and_10(9.9) True >>> between_4_and_10(19.7) False Other supported operators are ``|``, logical or, and ``~``, logical not: >>> smaller_equal_than_4 = ~bigger_than_4 >>> smaller_than_10_or_int = smaller_than_10 | is_int .. warning:: Note that Python conditional expressions are evaluated from left to right. As a result, the order of composition may matter, even though logical operators such as ``|`` and ``&`` are symmetric. For example: >>> is_int = qml.BooleanFn(lambda x: isinstance(x, int)) >>> has_bit_length_3 = qml.BooleanFn(lambda x: x.bit_length()==3) >>> (is_int & has_bit_length_3)(4) True >>> (is_int & has_bit_length_3)(2.3) False >>> (has_bit_length_3 & is_int)(2.3) AttributeError: 'float' object has no attribute 'bit_length' """ def __init__(self, fn): self.fn = fn functools.update_wrapper(self, fn) def __and__(self, other): return BooleanFn(lambda obj: self.fn(obj) and other.fn(obj)) def __or__(self, other): return BooleanFn(lambda obj: self.fn(obj) or other.fn(obj)) def __invert__(self): return BooleanFn(lambda obj: not self.fn(obj))
[docs] def __call__(self, obj): return self.fn(obj)