Source code for torch.autograd.function
import functools
import inspect
import itertools
import warnings
from collections import OrderedDict
from typing import Any, List, Optional, Tuple
import torch
import torch._C as _C
import torch._functorch as _functorch
import torch.utils.hooks as hooks
from torch._C import _functions
from torch._functorch.autograd_function import custom_function_call
__all__ = [
"FunctionCtx",
"BackwardCFunction",
"FunctionMeta",
"Function",
"once_differentiable",
"traceable",
"InplaceFunction",
"NestedIOFunction",
]
# Unique id provider for each class inheriting from Function
# This is incremented in FunctionMeta during class definition
AUTOGRAD_FUNCTION_COUNTER = itertools.count()
# Formerly known as: _ContextMethodMixin
class FunctionCtx:
[docs] def save_for_backward(self, *tensors: torch.Tensor):
r"""Save given tensors for a future call to :func:`~Function.backward`.
``save_for_backward`` should be called at most once, only from inside the
:func:`forward` method, and only with tensors.
All tensors intended to be used in the backward pass should be saved
with ``save_for_backward`` (as opposed to directly on ``ctx``) to prevent
incorrect gradients and memory leaks, and enable the application of saved
tensor hooks. See :class:`torch.autograd.graph.saved_tensors_hooks`.
Note that if intermediary tensors, tensors that are neither inputs
nor outputs of :func:`forward`, are saved for backward, your custom Function
may not support double backward.
Custom Functions that do not support double backward should decorate their
:func:`backward` method with ``@once_differentiable`` so that performing
double backward raises an error. If you'd like to support double backward,
you can either recompute intermediaries based on the inputs during backward
or return the intermediaries as the outputs of the custom Function. See the
`double backward tutorial <https://pytorch.org/tutorials/intermediate/custom_function_double_backward_tutorial.html>`_
for more details.
In :func:`backward`, saved tensors can be accessed through the :attr:`saved_tensors`
attribute. Before returning them to the user, a check is made to ensure
they weren't used in any in-place operation that modified their content.
Arguments can also be ``None``. This is a no-op.
See :ref:`extending-autograd` for more details on how to use this method.
Example::
>>> # xdoctest: +REQUIRES(env:TORCH_DOCTEST_AUTOGRAD)
>>> class Func(Function):
>>> @staticmethod
>>> def forward(ctx, x: torch.Tensor, y: torch.Tensor, z: int):
>>> w = x * z
>>> out = x * y + y * z + w * y
>>> ctx.save_for_backward(x, y, w, out)
>>> ctx.z = z # z is not a tensor
>>> return out
>>>
>>> @staticmethod
>>> @once_differentiable
>>> def backward(ctx, grad_out):
>>> x, y, w, out = ctx.saved_tensors
>>> z = ctx.z
>>> gx = grad_out * (y + y * z)
>>> gy = grad_out * (x + z + w)
>>> gz = None
>>> return gx, gy, gz
>>>
>>> a = torch.tensor(1., requires_grad=True, dtype=torch.double)
>>> b = torch.tensor(2., requires_grad=True, dtype=torch.double)
>>> c = 4
>>> d = Func.apply(a, b, c)
"""
self.to_save = tensors
def save_for_forward(self, *tensors: torch.Tensor):
r"""Save given tensors for a future call to :func:`~Function.jvp`.
``save_for_forward`` should be only called once, from inside the :func:`forward`
method, and only be called with tensors.
In :func:`jvp`, saved objects can be accessed through the :attr:`saved_tensors`
attribute.
Arguments can also be ``None``. This is a no-op.
See :ref:`extending-autograd` for more details on how to use this method.
Example::
>>> # xdoctest: +SKIP
>>> class Func(torch.autograd.Function):
>>> @staticmethod
>>> def forward(ctx, x: torch.Tensor, y: torch.Tensor, z: int):
>>> ctx.save_for_backward(x, y)
>>> ctx.save_for_forward(x, y)
>>> ctx.z = z
>>> return x * y * z
>>>
>>> @staticmethod
>>> def jvp(ctx, x_t, y_t, _):
>>> x, y = ctx.saved_tensors
>>> z = ctx.z
>>> return z * (y * x_t + x * y_t)
>>>
>>> @staticmethod
>>> def vjp(ctx, grad_out):
>>> x, y = ctx.saved_tensors
>>> z = ctx.z
>>> return z * grad_out * y, z * grad_out * x, None
>>>
>>> a = torch.tensor(1., requires_grad=True, dtype=torch.double)
>>> t = torch.tensor(1., dtype=torch.double)
>>> b = torch.tensor(2., requires_grad=True, dtype=torch.double)
>>> c = 4
>>>
>>> with fwAD.dual_level():
>>> a_dual = fwAD.make_dual(a, t)
>>> d = Func.apply(a_dual, b, c)
"""
for tensor in tensors:
assert isinstance(tensor, torch.Tensor) or tensor is None, (
"save_for_forward expects all arguments to be tensors; you should "
"save non-tensors as attributes on ctx."
)
self.saved_for_forward = tensors
[docs] def mark_dirty(self, *args: torch.Tensor):
r"""Mark given tensors as modified in an in-place operation.
**This should be called at most once, only from inside the**
:func:`forward` **method, and all arguments should be inputs.**
Every tensor that's been modified in-place in a call to :func:`forward`
should be given to this function, to ensure correctness of our checks.
It doesn't matter whether the function is called before or after
modification.
Examples::
>>> # xdoctest: +REQUIRES(env:TORCH_DOCTEST_AUTOGRAD)
>>> class Inplace(Function):
>>> @staticmethod
>>> def forward(ctx, x):
>>> x_npy = x.numpy() # x_npy shares storage with x
>>> x_npy += 1
>>> ctx.mark_dirty(x)
>>> return x
>>>
>>> @staticmethod
>>> @once_differentiable
>>> def backward(ctx, grad_output):
>>> return grad_output
>>>
>>> a = torch.tensor(1., requires_grad=True, dtype=torch.double).clone()
>>> b = a * a
>>> Inplace.apply(a) # This would lead to wrong gradients!
>>> # but the engine would not know unless we mark_dirty
>>> # xdoctest: +SKIP
>>> b.backward() # RuntimeError: one of the variables needed for gradient
>>> # computation has been modified by an inplace operation
"""
self.dirty_tensors = args
def mark_shared_storage(self, *pairs):
warnings.warn(
"mark_shared_storage is deprecated. "
"Tensors with shared storages are automatically tracked. Note "
"that calls to `set_()` are not tracked"
)
[docs] def mark_non_differentiable(self, *args: torch.Tensor):
r"""Mark outputs as non-differentiable.
**This should be called at most once, only from inside the**
:func:`forward` **method, and all arguments should be tensor outputs.**
This will mark outputs as not requiring gradients, increasing the
efficiency of backward computation. You still need to accept a gradient
for each output in :meth:`~Function.backward`, but it's always going to
be a zero tensor with the same shape as the shape of a corresponding
output.
This is used e.g. for indices returned from a sort. See example::
>>> class Func(Function):
>>> @staticmethod
>>> def forward(ctx, x):
>>> sorted, idx = x.sort()
>>> ctx.mark_non_differentiable(idx)
>>> ctx.save_for_backward(x, idx)
>>> return sorted, idx
>>>
>>> @staticmethod
>>> @once_differentiable
>>> def backward(ctx, g1, g2): # still need to accept g2
>>> x, idx = ctx.saved_tensors
>>> grad_input = torch.zeros_like(x)
>>> grad_input.index_add_(0, idx, g1)
>>> return grad_input
"""
self.non_differentiable = args
[docs] def set_materialize_grads(self, value: bool):
r"""Set whether to materialize grad tensors. Default is ``True``.
**This should be called only from inside the** :func:`forward` **method**
If ``True``, undefined grad tensors will be expanded to tensors full of zeros
prior to calling the :func:`backward` and :func:`jvp` methods.
Example::
>>> # xdoctest: +REQUIRES(env:TORCH_DOCTEST_AUTOGRAD)
>>> class SimpleFunc(Function):
>>> @staticmethod
>>> def forward(ctx, x):
>>> return x.clone(), x.clone()
>>>
>>> @staticmethod
>>> @once_differentiable
>>> def backward(ctx, g1, g2):
>>> return g1 + g2 # No check for None necessary
>>>
>>> # We modify SimpleFunc to handle non-materialized grad outputs
>>> class Func(Function):
>>> @staticmethod
>>> def forward(ctx, x):
>>> ctx.set_materialize_grads(False)
>>> ctx.save_for_backward(x)
>>> return x.clone(), x.clone()
>>>
>>> @staticmethod
>>> @once_differentiable
>>> def backward(ctx, g1, g2):
>>> x, = ctx.saved_tensors
>>> grad_input = torch.zeros_like(x)
>>> if g1 is not None: # We must check for None now
>>> grad_input += g1
>>> if g2 is not None:
>>> grad_input += g2
>>> return grad_input
>>>
>>> a = torch.tensor(1., requires_grad=True)
>>> b, _ = Func.apply(a) # induces g2 to be undefined
"""
self.materialize_grads = value
# DO NOT USE: This is only defined to be able to load old serialized models
_ContextMethodMixin = FunctionCtx
class _HookMixin:
@staticmethod
def _register_hook(backward_hooks, hook):
if backward_hooks is None:
backward_hooks = OrderedDict()
handle = hooks.RemovableHandle(backward_hooks)
backward_hooks[handle.id] = hook
return backward_hooks, handle
[docs]class BackwardCFunction(_C._FunctionBase, FunctionCtx, _HookMixin):
r"""
This class is used for internal autograd work. Do not use.
"""
[docs] def apply(self, *args):
r"""
Apply method used when executing this Node during the backward
"""
# _forward_cls is defined by derived class
# The user should define either backward or vjp but never both.
backward_fn = self._forward_cls.backward # type: ignore[attr-defined]
vjp_fn = self._forward_cls.vjp # type: ignore[attr-defined]
if backward_fn is not Function.backward and vjp_fn is not Function.vjp:
raise RuntimeError(
"Implementing both 'backward' and 'vjp' for a custom "
"Function is not allowed. You should only implement one "
"of them."
)
user_fn = vjp_fn if vjp_fn is not Function.vjp else backward_fn
return user_fn(self, *args)
[docs] def apply_jvp(self, *args):
r"""
Apply method used when executing forward mode AD during the forward
"""
# _forward_cls is defined by derived class
return self._forward_cls.jvp(self, *args) # type: ignore[attr-defined]
def _compiled_autograd_key(self):
return self._forward_cls._compiled_autograd_key(self) # type: ignore[attr-defined]
def _warn_traceable_deprecated():
warnings.warn(
"The is_traceable field on torch.autograd.Function is deprecated "
"and will be removed in PyTorch 2.4.",
stacklevel=3,
)
class _IsTraceableWarning:
def __init__(self, value):
self.value = value
def __get__(self, obj, klass=None):
_warn_traceable_deprecated()
return self.value
class FunctionMeta(type):
"""Function metaclass.
This metaclass sets up the following properties:
_backward_cls: The Function class corresponding to the differentiated
version of this function (which is generated on the fly by this
metaclass).
"""
def __init__(cls, name, bases, attrs):
backward_fn = type(
name + "Backward", (BackwardCFunction,), {"_forward_cls": cls}
)
backward_fn._autograd_function_id = next(AUTOGRAD_FUNCTION_COUNTER) # type: ignore[attr-defined]
backward_fn._compiled_autograd_should_lift = attrs.get( # type: ignore[attr-defined]
"_compiled_autograd_should_lift", True
)
cls._backward_cls = backward_fn
if "is_traceable" in attrs:
if attrs["is_traceable"] is True:
_warn_traceable_deprecated()
# already emitted warning, no need to install _IsTraceableWarning
else:
cls.is_traceable = _IsTraceableWarning(attrs.pop("is_traceable"))
super().__init__(name, bases, attrs)
def __setattr__(cls, name, value):
if name == "is_traceable" and value is True:
warnings.warn(
"The is_traceable field on torch.autograd.Function is deprecated "
"and will be removed in PyTorch 2.4.",
stacklevel=2,
)
return super().__setattr__(name, value)
class _SingleLevelFunction(
_C._FunctionBase, FunctionCtx, _HookMixin, metaclass=FunctionMeta
):
@staticmethod
def forward(*args: Any, **kwargs: Any) -> Any:
r"""Define the forward of the custom autograd Function.
This function is to be overridden by all subclasses.
There are two ways to define forward:
Usage 1 (Combined forward and ctx)::
@staticmethod
def forward(ctx: Any, *args: Any, **kwargs: Any) -> Any:
pass
- It must accept a context ctx as the first argument, followed by any
number of arguments (tensors or other types).
- See :ref:`combining-forward-context` for more details
Usage 2 (Separate forward and ctx)::
@staticmethod
def forward(*args: Any, **kwargs: Any) -> Any:
pass
@staticmethod
def setup_context(ctx: Any, inputs: Tuple[Any, ...], output: Any) -> None:
pass
- The forward no longer accepts a ctx argument.
- Instead, you must also override the :meth:`torch.autograd.Function.setup_context`
staticmethod to handle setting up the ``ctx`` object.
``output`` is the output of the forward, ``inputs`` are a Tuple of inputs
to the forward.
- See :ref:`extending-autograd` for more details
The context can be used to store arbitrary data that can be then
retrieved during the backward pass. Tensors should not be stored
directly on `ctx` (though this is not currently enforced for
backward compatibility). Instead, tensors should be saved either with
:func:`ctx.save_for_backward` if they are intended to be used in
``backward`` (equivalently, ``vjp``) or :func:`ctx.save_for_forward`
if they are intended to be used for in ``jvp``.
"""
raise NotImplementedError(
"You must implement the forward function for custom autograd.Function."
)
@staticmethod
def setup_context(ctx: Any, inputs: Tuple[Any, ...], output: Any) -> Any:
r"""There are two ways to define the forward pass of an autograd.Function.
Either:
1. Override forward with the signature ``forward(ctx, *args, **kwargs)``.
``setup_context`` is not overridden. Setting up the ctx for backward
happens inside the ``forward``.
2. Override forward with the signature ``forward(*args, **kwargs)`` and
override ``setup_context``. Setting up the ctx for backward happens
inside ``setup_context`` (as opposed to inside the ``forward``)
See :meth:`torch.autograd.Function.forward` and :ref:`extending-autograd` for more details.
"""
raise NotImplementedError("setup_context is not implemented.")
@staticmethod
def backward(ctx: Any, *grad_outputs: Any) -> Any:
r"""Define a formula for differentiating the operation with backward mode automatic differentiation.
This function is to be overridden by all subclasses.
(Defining this function is equivalent to defining the ``vjp`` function.)
It must accept a context :attr:`ctx` as the first argument, followed by
as many outputs as the :func:`forward` returned (None will be passed in
for non tensor outputs of the forward function),
and it should return as many tensors, as there were inputs to
:func:`forward`. Each argument is the gradient w.r.t the given output,
and each returned value should be the gradient w.r.t. the
corresponding input. If an input is not a Tensor or is a Tensor not
requiring grads, you can just pass None as a gradient for that input.
The context can be used to retrieve tensors saved during the forward
pass. It also has an attribute :attr:`ctx.needs_input_grad` as a tuple
of booleans representing whether each input needs gradient. E.g.,
:func:`backward` will have ``ctx.needs_input_grad[0] = True`` if the
first input to :func:`forward` needs gradient computed w.r.t. the
output.
"""
raise NotImplementedError(
"You must implement either the backward or vjp method for "
"your custom autograd.Function to use it with backward "
"mode AD."
)
# vjp and backward are alias of each other
vjp = backward
@staticmethod
def jvp(ctx: Any, *grad_inputs: Any) -> Any:
r"""Define a formula for differentiating the operation with forward mode automatic differentiation.
This function is to be overridden by all subclasses.
It must accept a context :attr:`ctx` as the first argument, followed by
as many inputs as the :func:`forward` got (None will be passed in
for non tensor inputs of the forward function),
and it should return as many tensors as there were outputs to
:func:`forward`. Each argument is the gradient w.r.t the given input,
and each returned value should be the gradient w.r.t. the
corresponding output. If an output is not a Tensor or the function is not
differentiable with respect to that output, you can just pass None as a
gradient for that input.
You can use the :attr:`ctx` object to pass any value from the forward to this
functions.
"""
raise NotImplementedError(
"You must implement the jvp function for custom "
"autograd.Function to use it with forward mode AD."
)
[docs]class Function(_SingleLevelFunction):
r"""Base class to create custom `autograd.Function`.
To create a custom `autograd.Function`, subclass this class and implement
the :meth:`forward` and :meth:`backward` static methods. Then, to use your custom
op in the forward pass, call the class method ``apply``. Do not call
:meth:`forward` directly.
To ensure correctness and best performance, make sure you are calling the
correct methods on ``ctx`` and validating your backward function using
:func:`torch.autograd.gradcheck`.
See :ref:`extending-autograd` for more details on how to use this class.
Examples::
>>> # xdoctest: +REQUIRES(env:TORCH_DOCTEST_AUTOGRAD)
>>> class Exp(Function):
>>> @staticmethod
>>> def forward(ctx, i):
>>> result = i.exp()
>>> ctx.save_for_backward(result)
>>> return result
>>>
>>> @staticmethod
>>> def backward(ctx, grad_output):
>>> result, = ctx.saved_tensors
>>> return grad_output * result
>>>
>>> # Use it by calling the apply method:
>>> # xdoctest: +SKIP
>>> output = Exp.apply(input)
"""
def __init__(self, *args, **kwargs):
cls = self.__class__
warnings.warn(
f"{cls} should not be instantiated. Methods on autograd functions"
"are all static, so you should invoke them on the class itself. "
"Instantiating an autograd function will raise an "
"error in a future version of PyTorch.",
DeprecationWarning,
stacklevel=2,
)
def __call__(self, *args, **kwargs):
raise RuntimeError(
"Legacy autograd function with non-static forward method is deprecated. "
"Please use new-style autograd function with static forward method. "
"(Example: https://pytorch.org/docs/stable/autograd.html#torch.autograd.Function)"
)
# for the tracer
is_traceable = False
"""
Bool that specifies if PyTorch should attempt to autogenerate
:func:`torch.vmap` support for this autograd.Function. You may set this to
True only if this autograd.Function's forward, backward, and jvp (if they
exist) are written using PyTorch operations; otherwise, please override
:meth:`torch.autograd.Function.vmap` to add support for :func:`torch.vmap`.
Please see :ref:`func-autograd-function` for more details.
"""
generate_vmap_rule = False
[docs] @staticmethod
def vmap(info, in_dims, *args):
r"""Define the behavior for this autograd.Function underneath :func:`torch.vmap`.
For a :func:`torch.autograd.Function` to support
:func:`torch.vmap`, you must either override this static method, or set
``generate_vmap_rule`` to ``True`` (you may not do both).
If you choose to override this staticmethod: it must accept
- an ``info`` object as the first argument. ``info.batch_size``
specifies the size of the dimension being vmapped over,
while ``info.randomness`` is the randomness option passed to
:func:`torch.vmap`.
- an ``in_dims`` tuple as the second argument.
For each arg in ``args``, ``in_dims`` has a corresponding
``Optional[int]``. It is ``None`` if the arg is not a Tensor or if
the arg is not being vmapped over, otherwise, it is an integer
specifying what dimension of the Tensor is being vmapped over.
- ``*args``, which is the same as the args to :meth:`~Function.forward`.
The return of the vmap staticmethod is a tuple of ``(output, out_dims)``.
Similar to ``in_dims``, ``out_dims`` should be of the same structure as
``output`` and contain one ``out_dim`` per output that specifies if the
output has the vmapped dimension and what index it is in.
Please see :ref:`func-autograd-function` for more details.
"""
raise NotImplementedError(
"To use autograd.Function with vmap, you must either override the "
"vmap staticmethod or set generate_vmap_rule=True."
)
@classmethod
def apply(cls, *args, **kwargs):
def bind_default_args(func, *args, **kwargs):
signature = inspect.signature(func)
bound_args = signature.bind(*args, **kwargs)
bound_args.apply_defaults()
return bound_args.args
is_setup_ctx_defined = cls.setup_context != _SingleLevelFunction.setup_context
if is_setup_ctx_defined:
args = bind_default_args(cls.forward, *args, **kwargs)
if not torch._C._are_functorch_transforms_active():
# See NOTE: [functorch vjp and autograd interaction]
args = _functorch.utils.unwrap_dead_wrappers(args)
return super().apply(*args, **kwargs) # type: ignore[misc]
if not is_setup_ctx_defined:
raise RuntimeError(
"In order to use an autograd.Function with functorch transforms "
"(vmap, grad, jvp, jacrev, ...), it must override the setup_context "
"staticmethod. For more details, please see "
"https://pytorch.org/docs/main/notes/extending.func.html"
)
return custom_function_call(cls, *args, **kwargs)
@staticmethod
def _compiled_autograd_key(ctx):
return (ctx._autograd_function_id,)
[docs]def once_differentiable(fn):
@functools.wraps(fn)
def wrapper(ctx, *args):
with torch.no_grad():
outputs = fn(ctx, *args)
if not torch.is_grad_enabled():
return outputs
# If any of the inputs have requires_grad=True, we force the outputs
# to have requires_grad=True but point to a grad_fn which throws an
# error message during (double) back-propagation.
# XXX: this is only an approximation of requires_grad - there's no way
# to figure out if fn didn't use ctx.saved_tensors and as a result
# some Tensors might require grad, even if no args do.
# Unfortunately, this leads to unexpected error messages ("no nodes
# require computing gradients"), but I don't have a better idea.
# These functions would raise an error in backward anyway.
requires_grad = any(
isinstance(arg, torch.Tensor) and arg.requires_grad for arg in args
)
if not requires_grad:
return outputs
if not isinstance(outputs, tuple):
outputs = (outputs,)
err_fn = _functions.DelayedError(
b"trying to differentiate twice a function that was marked "
b"with @once_differentiable",
len(outputs),
)
# Create aliases of each output that has requires_grad=True. We need
# at least one of the inputs to err_fn to require grad so that the
# output will have a grad_fn.
def fake_requires_grad(var):
if var is not None:
var = var.detach()
var.requires_grad = True
return var
return err_fn(*[fake_requires_grad(v) for v in outputs])
return wrapper
def traceable(fn_cls):
r"""Mark Function as traceable for the JIT.
Traceable functions have additional restrictions - they can't pass any
data-dependent values to backward (e.g. Prod passes the output, which makes
it non-traceable), and their backward should be implemented entirely in terms
of operations on autograd Tensors in all cases.
DON'T USE THIS DECORATOR. IT IS FOR INTERNAL USE ONLY AND SHOULD BE HANDLED WITH
CARE (or can give incorrect results otherwise).
"""
warnings.warn(
"torch.autograd.function.traceable is deprecated "
"and will be removed in PyTorch 2.4.",
stacklevel=2,
)
fn_cls.is_traceable = True
return fn_cls
[docs]class InplaceFunction(Function):
r"""
This class is here only for backward compatibility reasons.
Use :class:`Function` instead of this for any new use case.
"""
def __init__(self, inplace=False):
super().__init__()
self.inplace = inplace
def _nested_map(condition, fn, condition_msg=None):
def _map(obj):
if condition(obj):
return fn(obj)
elif obj is None:
return None
elif isinstance(obj, (list, tuple)):
mapped = (_map(x) for x in obj)
if hasattr(obj, "_fields"):
# obj is namedtuple
return type(obj)(*mapped)
return type(obj)(mapped)
elif isinstance(obj, dict):
return {x: _map(obj[x]) for x in obj}
else:
raise ValueError(
"Auto nesting doesn't know how to process "
"an input object of type "
+ torch.typename(obj)
+ (
". Accepted types: " + condition_msg + ", or lists/tuples of them"
if condition_msg
else ""
)
)
return _map
def _jit_unwrap_structured(obj):
if hasattr(obj, "_jit_unwrap"):
return obj._jit_unwrap()
return obj
def _iter_filter(condition, allow_unknown=False, condition_msg=None, conversion=None):
def _iter(obj):
if conversion is not None:
obj = conversion(obj)
if condition(obj):
yield obj
elif obj is None:
return
elif isinstance(obj, (list, tuple)):
for o in obj:
yield from _iter(o)
elif isinstance(obj, dict):
# We only accept primitive key types, so we needn't inspect them
for o in obj.values():
yield from _iter(o)
elif allow_unknown:
yield obj
else:
raise ValueError(
"Auto nesting doesn't know how to process "
"an input object of type "
+ torch.typename(obj)
+ (
". Accepted types: " + condition_msg + ", or lists/tuples of them"
if condition_msg
else ""
)
)
return _iter
def _unflatten(input, proto):
# unflatten a list or tuple input into a nested list/tuple structure
# specified by proto
def unflatten_helper(input, proto):
res: List[Optional[torch.Tensor]] = []
if hasattr(proto, "_jit_wrap"):
return proto._jit_wrap(input)
if not isinstance(proto, (list, tuple)):
return input[0], input[1:]
for e in proto:
if e is None:
res.append(e)
else:
res_e, input = unflatten_helper(input, e)
res.append(res_e)
return type(proto)(res), input
return unflatten_helper(input, proto)[0]
_iter_jit_values = _iter_filter(
lambda o: o is None or isinstance(o, torch._C.Value),
condition_msg="jit's Values or None",
)
_iter_tensors = _iter_filter(
lambda x: isinstance(x, torch.Tensor),
condition_msg="Tensors",
conversion=_jit_unwrap_structured,
)
_iter_tensors_permissive = _iter_filter(
lambda x: isinstance(x, torch.Tensor),
allow_unknown=True,
condition_msg="Tensors (permissive)",
)
_iter_None_tensors = _iter_filter(
lambda o: o is None or isinstance(o, torch.Tensor), condition_msg="Tensors or None"
)
_map_tensor_data = _nested_map(
lambda x: isinstance(x, torch.Tensor), lambda o: o.data, condition_msg="Tensors"
)
[docs]class NestedIOFunction(Function):
r"""
This class is here only for backward compatibility reasons.
Use :class:`Function` instead of this for any new use case.
"""
# The 'type: ignore' statements are needed here because these functions are declared as '@staticmethod' in the
# superclass (Function) but are instance methods here, which mypy reports as incompatible.
def _do_forward(self, *input):
self._nested_input = input
flat_input = tuple(_iter_tensors(input))
flat_output = super()._do_forward(*flat_input) # type: ignore[misc]
nested_output = self._nested_output
nested_tensors = _unflatten(flat_output, self._nested_output)
return nested_tensors
def _do_backward(self, gradients, retain_variables):
self.retain_variables = retain_variables
result = super()._do_backward(gradients, retain_variables) # type: ignore[misc]
if not retain_variables:
del self._nested_output
del self._to_save_nested
return result
[docs] def backward(self, *gradients: Any) -> Any: # type: ignore[override]
r"""
Shared backward utility.
"""
nested_gradients = _unflatten(gradients, self._nested_output)
result = self.backward_extended(*nested_gradients) # type: ignore[func-returns-value]
return tuple(_iter_None_tensors(result))
__call__ = _do_forward
[docs] def forward(self, *args: Any) -> Any: # type: ignore[override]
r"""
Shared forward utility.
"""
nested_tensors = _map_tensor_data(self._nested_input)
result = self.forward_extended(*nested_tensors) # type: ignore[func-returns-value]
del self._nested_input
self._nested_output = result
return tuple(_iter_tensors(result))
[docs] def save_for_backward(self, *args: Any) -> None:
r"""
See :meth:`Function.save_for_backward`.
"""
self.to_save = tuple(_iter_tensors(args))
self._to_save_nested = args
@property
def saved_tensors(self):
r"""
See :meth:`Function.saved_tensors`.
"""
flat_tensors = super().saved_tensors # type: ignore[misc]
return _unflatten(flat_tensors, self._to_save_nested)
[docs] def mark_dirty(self, *args: Any, **kwargs: Any) -> None:
r"""
See :meth:`Function.mark_dirty`.
"""
self.dirty_tensors = tuple(_iter_tensors((args, kwargs)))
[docs] def mark_non_differentiable(self, *args: Any, **kwargs: Any) -> None:
r"""
See :meth:`Function.mark_non_differentiable`.
"""
self.non_differentiable = tuple(_iter_tensors((args, kwargs)))
[docs] def forward_extended(self, *input: Any) -> None:
r"""
User defined forward.
"""
raise NotImplementedError
[docs] def backward_extended(self, *grad_output: Any) -> None:
r"""
User defined backward.
"""
raise NotImplementedError
