# Copyright 2021-2024 Cambridge Quantum Computing Ltd.
#
# 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.
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"""
Numerical Backend
=================
Module unifying the use of numerical backends for lambeq. This module is
used to provide a common interface to different numerical backends,
such as NumPy, JAX, PyTorch, and TensorFlow.
"""
from __future__ import annotations
from contextlib import contextmanager
from types import ModuleType
from typing import Callable, Generator
[docs]class Backend:
"""
A matrix backend.
Parameters:
module : The main module of the backend.
array : The array class of the backend.
"""
[docs] def __init__(self, module: ModuleType, array: Callable | None = None):
self.module, self.array = module, array or module.array
def __getattr__(self, attr):
return getattr(self.module, attr)
@property
def name(self):
return self.__class__.__name__.lower()
[docs]class NumPy(Backend):
""" NumPy backend. """
[docs] def __init__(self):
import numpy
super().__init__(numpy)
[docs]class JAX(Backend):
""" JAX backend. """
[docs] def __init__(self):
import jax
super().__init__(jax.numpy)
[docs]class PyTorch(Backend):
""" PyTorch backend. """
[docs] def __init__(self):
import torch
super().__init__(torch, array=torch.as_tensor)
[docs]class TensorFlow(Backend):
""" TensorFlow backend. """
[docs] def __init__(self):
import tensorflow.experimental.numpy as tnp
from tensorflow.python.ops.numpy_ops import np_config
np_config.enable_numpy_behavior()
super().__init__(tnp)
BACKENDS = {
'numpy': NumPy,
'jax': JAX,
'pytorch': PyTorch,
'tensorflow': TensorFlow,
}
[docs]@contextmanager
def backend(name: str | None = None,
_stack=['numpy'], # noqa: B006
_cache=dict()) -> Generator[Backend, None, None]: # noqa: B006
"""
Context manager for matrix backend.
Parameters:
name : The name of the backend, default is ``"numpy"``.
"""
name = name or _stack[-1]
_stack.append(name)
try:
if name not in _cache:
_cache[name] = BACKENDS[name]()
yield _cache[name]
finally:
_stack.pop()
[docs]def set_backend(name: str) -> None:
"""
Override the default backend.
Parameters:
name : The name of the backend.
"""
backend.__wrapped__.__defaults__[1][-1] = name # type: ignore[attr-defined] # noqa: E501
[docs]def get_backend() -> Backend:
"""
Get the current backend.
Example
-------
>>> set_backend('jax')
>>> assert isinstance(get_backend(), JAX)
>>> set_backend('numpy')
>>> assert isinstance(get_backend(), NumPy)
"""
with backend() as result:
return result