Source code for pennylane.boolean_fn
# Copyright 2018-2024 Xanadu Quantum Technologies Inc.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
# http://www.apache.org/licenses/LICENSE-2.0
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# pylint: disable=protected-access
"""
Contains a utility class ``BooleanFn`` that allows logical composition
of functions with boolean output.
"""
import functools
# pylint: disable=unnecessary-lambda
[docs]class BooleanFn:
r"""Wrapper for simple callables with Boolean output that can be
manipulated and combined with bitwise operators.
Args:
fn (callable): Function to be wrapped. It can accept any number
of arguments, and must return a Boolean.
**Example**
Consider functions that filter numbers to lie within a certain domain.
We may wrap them using ``BooleanFn``:
.. code-block:: python
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):
.. code-block:: python
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, name=None):
self.fn = fn
self.name = name or self.fn.__name__
functools.update_wrapper(self, fn)
def __and__(self, other):
return And(self, other)
def __or__(self, other):
return Or(self, other)
def __xor__(self, other):
return Xor(self, other)
def __invert__(self):
return Not(self)
def __call__(self, *args, **kwargs):
return self.fn(*args, **kwargs)
def __repr__(self):
return f"BooleanFn({self.name})" if not (self.bitwise or self.conditional) else self.name
@property
def bitwise(self):
"""Determine whether the wrapped callable performs a bitwise operation or not.
This checks for the ``operands`` attribute that should be defined by it."""
return bool(getattr(self, "operands", tuple()))
@property
def conditional(self):
"""Determine whether the wrapped callable is for a conditional or not.
This checks for the ``condition`` attribute that should be defined by it."""
return bool(getattr(self, "condition", None))
[docs]class And(BooleanFn):
"""Developer facing class for implemeting bitwise ``AND`` for callables
wrapped up with :class:`BooleanFn <pennylane.BooleanFn>`.
Args:
left (~.BooleanFn): Left operand in the bitwise expression.
right (~.BooleanFn): Right operand in the bitwise expression.
"""
def __init__(self, left, right):
self.operands = (left, right)
if any(getattr(opr, "condition", None) for opr in self.operands):
self.condition = tuple(getattr(opr, "condition", ()) for opr in self.operands)
super().__init__(
lambda *args, **kwargs: left(*args, **kwargs) and right(*args, **kwargs),
f"And({left.name}, {right.name})",
)
def __str__(self):
return f"{self.operands[0].name} & {self.operands[1].name}"
[docs]class Or(BooleanFn):
"""Developer facing class for implemeting bitwise ``OR`` for callables
wrapped up with :class:`BooleanFn <pennylane.BooleanFn>`.
Args:
left (~.BooleanFn): Left operand in the bitwise expression.
right (~.BooleanFn): Right operand in the bitwise expression.
"""
def __init__(self, left, right):
self.operands = (left, right)
if any(getattr(opr, "condition", None) for opr in self.operands):
self.condition = tuple(getattr(opr, "condition", ()) for opr in self.operands)
super().__init__(
lambda *args, **kwargs: left(*args, **kwargs) or right(*args, **kwargs),
f"Or({left.name}, {right.name})",
)
def __str__(self):
return f"{self.operands[0].name} | {self.operands[1].name}"
[docs]class Xor(BooleanFn):
"""Developer facing class for implemeting bitwise ``XOR`` for callables
wrapped up with :class:`BooleanFn <pennylane.BooleanFn>`.
Args:
left (~.BooleanFn): Left operand in the bitwise expression.
right (~.BooleanFn): Right operand in the bitwise expression.
"""
def __init__(self, left, right):
self.operands = (left, right)
if any(getattr(opr, "condition", None) for opr in self.operands):
self.condition = tuple(getattr(opr, "condition", ()) for opr in self.operands)
super().__init__(
lambda *args, **kwargs: left(*args, **kwargs) ^ right(*args, **kwargs),
f"Xor({left.name}, {right.name})",
)
def __str__(self):
return f"{self.operands[0].name} ^ {self.operands[1].name}"
[docs]class Not(BooleanFn):
"""Developer facing class for implemeting bitwise ``NOT`` for callables
wrapped up with :class:`BooleanFn <pennylane.BooleanFn>`.
Args:
left (~.BooleanFn): Left operand in the bitwise expression.
"""
def __init__(self, left):
self.operands = (left,)
if any(getattr(opr, "condition", None) for opr in self.operands):
self.condition = tuple(getattr(opr, "condition", ()) for opr in self.operands)
super().__init__(
lambda *args, **kwargs: not left(*args, **kwargs),
f"Not({left.name})",
)
def __str__(self):
return f"~{self.operands[0].name}"
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