""" PyTorch Feature Extraction Helpers
A collection of classes, functions, modules to help extract features from models
and provide a common interface for describing them.
The return_layers, module re-writing idea inspired by torchvision IntermediateLayerGetter
https://github.com/pytorch/vision/blob/d88d8961ae51507d0cb680329d985b1488b1b76b/torchvision/models/_utils.py
Hacked together by / Copyright 2020 Ross Wightman
"""
from collections import OrderedDict, defaultdict
from copy import deepcopy
from functools import partial
from typing import Dict, List, Optional, Sequence, Tuple, Union
import torch
import torch.nn as nn
from timm.layers import Format, _assert
from ._manipulate import checkpoint
__all__ = [
'FeatureInfo', 'FeatureHooks', 'FeatureDictNet', 'FeatureListNet', 'FeatureHookNet', 'FeatureGetterNet',
'feature_take_indices'
]
def feature_take_indices(
num_features: int,
indices: Optional[Union[int, List[int]]] = None,
as_set: bool = False,
) -> Tuple[List[int], int]:
""" Determine the absolute feature indices to 'take' from.
Note: This function can be called in forward() so must be torchscript compatible,
which requires some incomplete typing and workaround hacks.
Args:
num_features: total number of features to select from
indices: indices to select,
None -> select all
int -> select last n
list/tuple of int -> return specified (-ve indices specify from end)
as_set: return as a set
Returns:
List (or set) of absolute (from beginning) indices, Maximum index
"""
if indices is None:
indices = num_features # all features if None
if isinstance(indices, int):
# convert int -> last n indices
_assert(0 < indices <= num_features, f'last-n ({indices}) is out of range (1 to {num_features})')
take_indices = [num_features - indices + i for i in range(indices)]
else:
take_indices: List[int] = []
for i in indices:
idx = num_features + i if i < 0 else i
_assert(0 <= idx < num_features, f'feature index {idx} is out of range (0 to {num_features - 1})')
take_indices.append(idx)
if not torch.jit.is_scripting() and as_set:
return set(take_indices), max(take_indices)
return take_indices, max(take_indices)
def _out_indices_as_tuple(x: Union[int, Tuple[int, ...]]) -> Tuple[int, ...]:
if isinstance(x, int):
# if indices is an int, take last N features
return tuple(range(-x, 0))
return tuple(x)
OutIndicesT = Union[int, Tuple[int, ...]]
class FeatureInfo:
def __init__(
self,
feature_info: List[Dict],
out_indices: OutIndicesT,
):
out_indices = _out_indices_as_tuple(out_indices)
prev_reduction = 1
for i, fi in enumerate(feature_info):
# sanity check the mandatory fields, there may be additional fields depending on the model
assert 'num_chs' in fi and fi['num_chs'] > 0
assert 'reduction' in fi and fi['reduction'] >= prev_reduction
prev_reduction = fi['reduction']
assert 'module' in fi
fi.setdefault('index', i)
self.out_indices = out_indices
self.info = feature_info
def from_other(self, out_indices: OutIndicesT):
out_indices = _out_indices_as_tuple(out_indices)
return FeatureInfo(deepcopy(self.info), out_indices)
def get(self, key: str, idx: Optional[Union[int, List[int]]] = None):
""" Get value by key at specified index (indices)
if idx == None, returns value for key at each output index
if idx is an integer, return value for that feature module index (ignoring output indices)
if idx is a list/tuple, return value for each module index (ignoring output indices)
"""
if idx is None:
return [self.info[i][key] for i in self.out_indices]
if isinstance(idx, (tuple, list)):
return [self.info[i][key] for i in idx]
else:
return self.info[idx][key]
def get_dicts(self, keys: Optional[List[str]] = None, idx: Optional[Union[int, List[int]]] = None):
""" return info dicts for specified keys (or all if None) at specified indices (or out_indices if None)
"""
if idx is None:
if keys is None:
return [self.info[i] for i in self.out_indices]
else:
return [{k: self.info[i][k] for k in keys} for i in self.out_indices]
if isinstance(idx, (tuple, list)):
return [self.info[i] if keys is None else {k: self.info[i][k] for k in keys} for i in idx]
else:
return self.info[idx] if keys is None else {k: self.info[idx][k] for k in keys}
def channels(self, idx: Optional[Union[int, List[int]]] = None):
""" feature channels accessor
"""
return self.get('num_chs', idx)
def reduction(self, idx: Optional[Union[int, List[int]]] = None):
""" feature reduction (output stride) accessor
"""
return self.get('reduction', idx)
def module_name(self, idx: Optional[Union[int, List[int]]] = None):
""" feature module name accessor
"""
return self.get('module', idx)
def __getitem__(self, item):
return self.info[item]
def __len__(self):
return len(self.info)
class FeatureHooks:
""" Feature Hook Helper
This module helps with the setup and extraction of hooks for extracting features from
internal nodes in a model by node name.
FIXME This works well in eager Python but needs redesign for torchscript.
"""
def __init__(
self,
hooks: Sequence[Union[str, Dict]],
named_modules: dict,
out_map: Sequence[Union[int, str]] = None,
default_hook_type: str = 'forward',
):
# setup feature hooks
self._feature_outputs = defaultdict(OrderedDict)
self._handles = []
modules = {k: v for k, v in named_modules}
for i, h in enumerate(hooks):
hook_name = h if isinstance(h, str) else h['module']
m = modules[hook_name]
hook_id = out_map[i] if out_map else hook_name
hook_fn = partial(self._collect_output_hook, hook_id)
hook_type = default_hook_type
if isinstance(h, dict):
hook_type = h.get('hook_type', default_hook_type)
if hook_type == 'forward_pre':
handle = m.register_forward_pre_hook(hook_fn)
elif hook_type == 'forward':
handle = m.register_forward_hook(hook_fn)
else:
assert False, "Unsupported hook type"
self._handles.append(handle)
def _collect_output_hook(self, hook_id, *args):
x = args[-1] # tensor we want is last argument, output for fwd, input for fwd_pre
if isinstance(x, tuple):
x = x[0] # unwrap input tuple
self._feature_outputs[x.device][hook_id] = x
def get_output(self, device) -> Dict[str, torch.tensor]:
output = self._feature_outputs[device]
self._feature_outputs[device] = OrderedDict() # clear after reading
return output
def _module_list(module, flatten_sequential=False):
# a yield/iter would be better for this but wouldn't be compatible with torchscript
ml = []
for name, module in module.named_children():
if flatten_sequential and isinstance(module, nn.Sequential):
# first level of Sequential containers is flattened into containing model
for child_name, child_module in module.named_children():
combined = [name, child_name]
ml.append(('_'.join(combined), '.'.join(combined), child_module))
else:
ml.append((name, name, module))
return ml
def _get_feature_info(net, out_indices: OutIndicesT):
feature_info = getattr(net, 'feature_info')
if isinstance(feature_info, FeatureInfo):
return feature_info.from_other(out_indices)
elif isinstance(feature_info, (list, tuple)):
return FeatureInfo(net.feature_info, out_indices)
else:
assert False, "Provided feature_info is not valid"
def _get_return_layers(feature_info, out_map):
module_names = feature_info.module_name()
return_layers = {}
for i, name in enumerate(module_names):
return_layers[name] = out_map[i] if out_map is not None else feature_info.out_indices[i]
return return_layers
class FeatureDictNet(nn.ModuleDict):
""" Feature extractor with OrderedDict return
Wrap a model and extract features as specified by the out indices, the network is
partially re-built from contained modules.
There is a strong assumption that the modules have been registered into the model in the same
order as they are used. There should be no reuse of the same nn.Module more than once, including
trivial modules like `self.relu = nn.ReLU`.
Only submodules that are directly assigned to the model class (`model.feature1`) or at most
one Sequential container deep (`model.features.1`, with flatten_sequent=True) can be captured.
All Sequential containers that are directly assigned to the original model will have their
modules assigned to this module with the name `model.features.1` being changed to `model.features_1`
"""
def __init__(
self,
model: nn.Module,
out_indices: OutIndicesT = (0, 1, 2, 3, 4),
out_map: Sequence[Union[int, str]] = None,
output_fmt: str = 'NCHW',
feature_concat: bool = False,
flatten_sequential: bool = False,
):
"""
Args:
model: Model from which to extract features.
out_indices: Output indices of the model features to extract.
out_map: Return id mapping for each output index, otherwise str(index) is used.
feature_concat: Concatenate intermediate features that are lists or tuples instead of selecting
first element e.g. `x[0]`
flatten_sequential: Flatten first two-levels of sequential modules in model (re-writes model modules)
"""
super(FeatureDictNet, self).__init__()
self.feature_info = _get_feature_info(model, out_indices)
self.output_fmt = Format(output_fmt)
self.concat = feature_concat
self.grad_checkpointing = False
self.return_layers = {}
return_layers = _get_return_layers(self.feature_info, out_map)
modules = _module_list(model, flatten_sequential=flatten_sequential)
remaining = set(return_layers.keys())
layers = OrderedDict()
for new_name, old_name, module in modules:
layers[new_name] = module
if old_name in remaining:
# return id has to be consistently str type for torchscript
self.return_layers[new_name] = str(return_layers[old_name])
remaining.remove(old_name)
if not remaining:
break
assert not remaining and len(self.return_layers) == len(return_layers), \
f'Return layers ({remaining}) are not present in model'
self.update(layers)
def set_grad_checkpointing(self, enable: bool = True):
self.grad_checkpointing = enable
def _collect(self, x) -> (Dict[str, torch.Tensor]):
out = OrderedDict()
for i, (name, module) in enumerate(self.items()):
if self.grad_checkpointing and not torch.jit.is_scripting():
# Skipping checkpoint of first module because need a gradient at input
# Skipping last because networks with in-place ops might fail w/ checkpointing enabled
# NOTE: first_or_last module could be static, but recalc in is_scripting guard to avoid jit issues
first_or_last_module = i == 0 or i == max(len(self) - 1, 0)
x = module(x) if first_or_last_module else checkpoint(module, x)
else:
x = module(x)
if name in self.return_layers:
out_id = self.return_layers[name]
if isinstance(x, (tuple, list)):
# If model tap is a tuple or list, concat or select first element
# FIXME this may need to be more generic / flexible for some nets
out[out_id] = torch.cat(x, 1) if self.concat else x[0]
else:
out[out_id] = x
return out
def forward(self, x) -> Dict[str, torch.Tensor]:
return self._collect(x)
class FeatureListNet(FeatureDictNet):
""" Feature extractor with list return
A specialization of FeatureDictNet that always returns features as a list (values() of dict).
"""
def __init__(
self,
model: nn.Module,
out_indices: OutIndicesT = (0, 1, 2, 3, 4),
output_fmt: str = 'NCHW',
feature_concat: bool = False,
flatten_sequential: bool = False,
):
"""
Args:
model: Model from which to extract features.
out_indices: Output indices of the model features to extract.
feature_concat: Concatenate intermediate features that are lists or tuples instead of selecting
first element e.g. `x[0]`
flatten_sequential: Flatten first two-levels of sequential modules in model (re-writes model modules)
"""
super().__init__(
model,
out_indices=out_indices,
output_fmt=output_fmt,
feature_concat=feature_concat,
flatten_sequential=flatten_sequential,
)
def forward(self, x) -> (List[torch.Tensor]):
return list(self._collect(x).values())
class FeatureHookNet(nn.ModuleDict):
""" FeatureHookNet
Wrap a model and extract features specified by the out indices using forward/forward-pre hooks.
If `no_rewrite` is True, features are extracted via hooks without modifying the underlying
network in any way.
If `no_rewrite` is False, the model will be re-written as in the
FeatureList/FeatureDict case by folding first to second (Sequential only) level modules into this one.
FIXME this does not currently work with Torchscript, see FeatureHooks class
"""
def __init__(
self,
model: nn.Module,
out_indices: OutIndicesT = (0, 1, 2, 3, 4),
out_map: Optional[Sequence[Union[int, str]]] = None,
return_dict: bool = False,
output_fmt: str = 'NCHW',
no_rewrite: Optional[bool] = None,
flatten_sequential: bool = False,
default_hook_type: str = 'forward',
):
"""
Args:
model: Model from which to extract features.
out_indices: Output indices of the model features to extract.
out_map: Return id mapping for each output index, otherwise str(index) is used.
return_dict: Output features as a dict.
no_rewrite: Enforce that model is not re-written if True, ie no modules are removed / changed.
flatten_sequential arg must also be False if this is set True.
flatten_sequential: Re-write modules by flattening first two levels of nn.Sequential containers.
default_hook_type: The default hook type to use if not specified in model.feature_info.
"""
super().__init__()
assert not torch.jit.is_scripting()
self.feature_info = _get_feature_info(model, out_indices)
self.return_dict = return_dict
self.output_fmt = Format(output_fmt)
self.grad_checkpointing = False
if no_rewrite is None:
no_rewrite = not flatten_sequential
layers = OrderedDict()
hooks = []
if no_rewrite:
assert not flatten_sequential
if hasattr(model, 'reset_classifier'): # make sure classifier is removed?
model.reset_classifier(0)
layers['body'] = model
hooks.extend(self.feature_info.get_dicts())
else:
modules = _module_list(model, flatten_sequential=flatten_sequential)
remaining = {
f['module']: f['hook_type'] if 'hook_type' in f else default_hook_type
for f in self.feature_info.get_dicts()
}
for new_name, old_name, module in modules:
layers[new_name] = module
for fn, fm in module.named_modules(prefix=old_name):
if fn in remaining:
hooks.append(dict(module=fn, hook_type=remaining[fn]))
del remaining[fn]
if not remaining:
break
assert not remaining, f'Return layers ({remaining}) are not present in model'
self.update(layers)
self.hooks = FeatureHooks(hooks, model.named_modules(), out_map=out_map)
def set_grad_checkpointing(self, enable: bool = True):
self.grad_checkpointing = enable
def forward(self, x):
for i, (name, module) in enumerate(self.items()):
if self.grad_checkpointing and not torch.jit.is_scripting():
# Skipping checkpoint of first module because need a gradient at input
# Skipping last because networks with in-place ops might fail w/ checkpointing enabled
# NOTE: first_or_last module could be static, but recalc in is_scripting guard to avoid jit issues
first_or_last_module = i == 0 or i == max(len(self) - 1, 0)
x = module(x) if first_or_last_module else checkpoint(module, x)
else:
x = module(x)
out = self.hooks.get_output(x.device)
return out if self.return_dict else list(out.values())
class FeatureGetterNet(nn.ModuleDict):
""" FeatureGetterNet
Wrap models with a feature getter method, like 'get_intermediate_layers'
"""
def __init__(
self,
model: nn.Module,
out_indices: OutIndicesT = 4,
out_map: Optional[Sequence[Union[int, str]]] = None,
return_dict: bool = False,
output_fmt: str = 'NCHW',
norm: bool = False,
prune: bool = True,
):
"""
Args:
model: Model to wrap.
out_indices: Indices of features to extract.
out_map: Remap feature names for dict output (WIP, not supported).
return_dict: Return features as dictionary instead of list (WIP, not supported).
norm: Apply final model norm to all output features (if possible).
"""
super().__init__()
if prune and hasattr(model, 'prune_intermediate_layers'):
# replace out_indices after they've been normalized, -ve indices will be invalid after prune
out_indices = model.prune_intermediate_layers(
out_indices,
prune_norm=not norm,
)
self.feature_info = _get_feature_info(model, out_indices)
self.model = model
self.out_indices = out_indices
self.out_map = out_map
self.return_dict = return_dict
self.output_fmt = Format(output_fmt)
self.norm = norm
def forward(self, x):
features = self.model.forward_intermediates(
x,
indices=self.out_indices,
norm=self.norm,
output_fmt=self.output_fmt,
intermediates_only=True,
)
return features