fastai/layers.py

"""Custom fastai layers and basic functions to grab them."""

# AUTOGENERATED! DO NOT EDIT! File to edit: ../nbs/01_layers.ipynb.

# %% ../nbs/01_layers.ipynb 2
from __future__ import annotations
from .imports import *
from .torch_imports import *
from .torch_core import *
from torch.nn.utils import weight_norm, spectral_norm

# %% auto 0
__all__ = ['NormType', 'inplace_relu', 'Mish', 'Swish', 'module', 'Identity', 'Lambda', 'PartialLambda', 'Flatten',
           'ToTensorBase', 'View', 'ResizeBatch', 'Debugger', 'sigmoid_range', 'SigmoidRange', 'AdaptiveConcatPool1d',
           'AdaptiveConcatPool2d', 'PoolType', 'adaptive_pool', 'PoolFlatten', 'BatchNorm', 'InstanceNorm',
           'BatchNorm1dFlat', 'LinBnDrop', 'sigmoid', 'sigmoid_', 'vleaky_relu', 'init_default', 'init_linear',
           'ConvLayer', 'AdaptiveAvgPool', 'MaxPool', 'AvgPool', 'trunc_normal_', 'Embedding', 'SelfAttention',
           'PooledSelfAttention2d', 'SimpleSelfAttention', 'icnr_init', 'PixelShuffle_ICNR', 'sequential',
           'SequentialEx', 'MergeLayer', 'Cat', 'SimpleCNN', 'ProdLayer', 'SEModule', 'ResBlock', 'SEBlock',
           'SEResNeXtBlock', 'SeparableBlock', 'TimeDistributed', 'swish', 'SwishJit', 'MishJitAutoFn', 'mish',
           'MishJit', 'ParameterModule', 'children_and_parameters', 'has_children', 'flatten_model', 'NoneReduce',
           'in_channels']

# %% ../nbs/01_layers.ipynb 6
def module(*flds, **defaults):
    "Decorator to create an `nn.Module` using `f` as `forward` method"
    pa = [inspect.Parameter(o, inspect.Parameter.POSITIONAL_OR_KEYWORD) for o in flds]
    pb = [inspect.Parameter(k, inspect.Parameter.POSITIONAL_OR_KEYWORD, default=v)
          for k,v in defaults.items()]
    params = pa+pb
    all_flds = [*flds,*defaults.keys()]

    def _f(f):
        class c(nn.Module):
            def __init__(self, *args, **kwargs):
                super().__init__()
                for i,o in enumerate(args): kwargs[all_flds[i]] = o
                kwargs = merge(defaults,kwargs)
                for k,v in kwargs.items(): setattr(self,k,v)
            __repr__ = basic_repr(all_flds)
            forward = f
        c.__signature__ = inspect.Signature(params)
        c.__name__ = c.__qualname__ = f.__name__
        c.__doc__  = f.__doc__
        return c
    return _f

# %% ../nbs/01_layers.ipynb 7
@module()
def Identity(self, x):
    "Do nothing at all"
    return x

# %% ../nbs/01_layers.ipynb 9
@module('func')
def Lambda(self, x):
    "An easy way to create a pytorch layer for a simple `func`"
    return self.func(x)

# %% ../nbs/01_layers.ipynb 11
class PartialLambda(Lambda):
    "Layer that applies `partial(func, **kwargs)`"
    def __init__(self, func, **kwargs):
        super().__init__(partial(func, **kwargs))
        self.repr = f'{func.__name__}, {kwargs}'

    def forward(self, x): return self.func(x)
    def __repr__(self): return f'{self.__class__.__name__}({self.repr})'

# %% ../nbs/01_layers.ipynb 13
@module(full=False)
def Flatten(self, x):
    "Flatten `x` to a single dimension, e.g. at end of a model. `full` for rank-1 tensor"
    return x.view(-1) if self.full else x.view(x.size(0), -1)  # Removed cast to Tensorbase

# %% ../nbs/01_layers.ipynb 15
@module(tensor_cls=TensorBase)
def ToTensorBase(self, x):
    "Convert x to TensorBase class"
    return self.tensor_cls(x)

# %% ../nbs/01_layers.ipynb 17
class View(Module):
    "Reshape `x` to `size`"
    def __init__(self, *size): self.size = size
    def forward(self, x): return x.view(self.size)

# %% ../nbs/01_layers.ipynb 19
class ResizeBatch(Module):
    "Reshape `x` to `size`, keeping batch dim the same size"
    def __init__(self, *size): self.size = size
    def forward(self, x): return x.view((x.size(0),) + self.size)

# %% ../nbs/01_layers.ipynb 21
@module()
def Debugger(self,x):
    "A module to debug inside a model."
    set_trace()
    return x

# %% ../nbs/01_layers.ipynb 22
def sigmoid_range(x, low, high):
    "Sigmoid function with range `(low, high)`"
    return torch.sigmoid(x) * (high - low) + low

# %% ../nbs/01_layers.ipynb 24
@module('low','high')
def SigmoidRange(self, x):
    "Sigmoid module with range `(low, high)`"
    return sigmoid_range(x, self.low, self.high)

# %% ../nbs/01_layers.ipynb 27
class AdaptiveConcatPool1d(Module):
    "Layer that concats `AdaptiveAvgPool1d` and `AdaptiveMaxPool1d`"
    def __init__(self, size=None):
        self.size = size or 1
        self.ap = nn.AdaptiveAvgPool1d(self.size)
        self.mp = nn.AdaptiveMaxPool1d(self.size)
    def forward(self, x): return torch.cat([self.mp(x), self.ap(x)], 1)

# %% ../nbs/01_layers.ipynb 28
class AdaptiveConcatPool2d(Module):
    "Layer that concats `AdaptiveAvgPool2d` and `AdaptiveMaxPool2d`"
    def __init__(self, size=None):
        self.size = size or 1
        self.ap = nn.AdaptiveAvgPool2d(self.size)
        self.mp = nn.AdaptiveMaxPool2d(self.size)
    def forward(self, x): return torch.cat([self.mp(x), self.ap(x)], 1)

# %% ../nbs/01_layers.ipynb 31
class PoolType: Avg,Max,Cat = 'Avg','Max','Cat'

# %% ../nbs/01_layers.ipynb 32
def adaptive_pool(pool_type):
    return nn.AdaptiveAvgPool2d if pool_type=='Avg' else nn.AdaptiveMaxPool2d if pool_type=='Max' else AdaptiveConcatPool2d

# %% ../nbs/01_layers.ipynb 33
class PoolFlatten(nn.Sequential):
    "Combine `nn.AdaptiveAvgPool2d` and `Flatten`."
    def __init__(self, pool_type=PoolType.Avg): super().__init__(adaptive_pool(pool_type)(1), Flatten())

# %% ../nbs/01_layers.ipynb 36
NormType = Enum('NormType', 'Batch BatchZero Weight Spectral Instance InstanceZero')

# %% ../nbs/01_layers.ipynb 37
def _get_norm(prefix, nf, ndim=2, zero=False, **kwargs):
    "Norm layer with `nf` features and `ndim` initialized depending on `norm_type`."
    assert 1 <= ndim <= 3
    bn = getattr(nn, f"{prefix}{ndim}d")(nf, **kwargs)
    if bn.affine:
        bn.bias.data.fill_(1e-3)
        bn.weight.data.fill_(0. if zero else 1.)
    return bn

# %% ../nbs/01_layers.ipynb 38
@delegates(nn.BatchNorm2d)
def BatchNorm(nf, ndim=2, norm_type=NormType.Batch, **kwargs):
    "BatchNorm layer with `nf` features and `ndim` initialized depending on `norm_type`."
    return _get_norm('BatchNorm', nf, ndim, zero=norm_type==NormType.BatchZero, **kwargs)

# %% ../nbs/01_layers.ipynb 39
@delegates(nn.InstanceNorm2d)
def InstanceNorm(nf, ndim=2, norm_type=NormType.Instance, affine=True, **kwargs):
    "InstanceNorm layer with `nf` features and `ndim` initialized depending on `norm_type`."
    return _get_norm('InstanceNorm', nf, ndim, zero=norm_type==NormType.InstanceZero, affine=affine, **kwargs)

# %% ../nbs/01_layers.ipynb 45
class BatchNorm1dFlat(nn.BatchNorm1d):
    "`nn.BatchNorm1d`, but first flattens leading dimensions"
    def forward(self, x):
        if x.dim()==2: return super().forward(x)
        *f,l = x.shape
        x = x.contiguous().view(-1,l)
        return super().forward(x).view(*f,l)

# %% ../nbs/01_layers.ipynb 47
class LinBnDrop(nn.Sequential):
    "Module grouping `BatchNorm1d`, `Dropout` and `Linear` layers"
    def __init__(self, n_in, n_out, bn=True, p=0., act=None, lin_first=False):
        layers = [BatchNorm(n_out if lin_first else n_in, ndim=1)] if bn else []
        if p != 0: layers.append(nn.Dropout(p))
        lin = [nn.Linear(n_in, n_out, bias=not bn)]
        if act is not None: lin.append(act)
        layers = lin+layers if lin_first else layers+lin
        super().__init__(*layers)

# %% ../nbs/01_layers.ipynb 51
def sigmoid(input, eps=1e-7):
    "Same as `torch.sigmoid`, plus clamping to `(eps,1-eps)"
    return input.sigmoid().clamp(eps,1-eps)

# %% ../nbs/01_layers.ipynb 52
def sigmoid_(input, eps=1e-7):
    "Same as `torch.sigmoid_`, plus clamping to `(eps,1-eps)"
    return input.sigmoid_().clamp_(eps,1-eps)

# %% ../nbs/01_layers.ipynb 53
from torch.nn.init import kaiming_uniform_,uniform_,xavier_uniform_,normal_

# %% ../nbs/01_layers.ipynb 54
def vleaky_relu(input, inplace=True):
    "`F.leaky_relu` with 0.3 slope"
    return F.leaky_relu(input, negative_slope=0.3, inplace=inplace)

# %% ../nbs/01_layers.ipynb 55
for o in F.relu,nn.ReLU,F.relu6,nn.ReLU6,F.leaky_relu,nn.LeakyReLU:
    o.__default_init__ = kaiming_uniform_

# %% ../nbs/01_layers.ipynb 56
for o in F.sigmoid,nn.Sigmoid,F.tanh,nn.Tanh,sigmoid,sigmoid_:
    o.__default_init__ = xavier_uniform_

# %% ../nbs/01_layers.ipynb 57
def init_default(m, func=nn.init.kaiming_normal_):
    "Initialize `m` weights with `func` and set `bias` to 0."
    if func and hasattr(m, 'weight'): func(m.weight)
    with torch.no_grad(): nested_callable(m, 'bias.fill_')(0.)
    return m

# %% ../nbs/01_layers.ipynb 58
def init_linear(m, act_func=None, init='auto', bias_std=0.01):
    if getattr(m,'bias',None) is not None and bias_std is not None:
        if bias_std != 0: normal_(m.bias, 0, bias_std)
        else: m.bias.data.zero_()
    if init=='auto':
        if act_func in (F.relu_,F.leaky_relu_): init = kaiming_uniform_
        else: init = nested_callable(act_func, '__class__.__default_init__')
        if init == noop: init = getcallable(act_func, '__default_init__')
    if callable(init): init(m.weight)

# %% ../nbs/01_layers.ipynb 60
def _conv_func(ndim=2, transpose=False):
    "Return the proper conv `ndim` function, potentially `transposed`."
    assert 1 <= ndim <=3
    return getattr(nn, f'Conv{"Transpose" if transpose else ""}{ndim}d')

# %% ../nbs/01_layers.ipynb 62
defaults.activation=nn.ReLU

# %% ../nbs/01_layers.ipynb 63
class ConvLayer(nn.Sequential):
    "Create a sequence of convolutional (`ni` to `nf`), ReLU (if `use_activ`) and `norm_type` layers."
    @delegates(nn.Conv2d)
    def __init__(self, ni, nf, ks=3, stride=1, padding=None, bias=None, ndim=2, norm_type=NormType.Batch, bn_1st=True,
                 act_cls=defaults.activation, transpose=False, init='auto', xtra=None, bias_std=0.01, **kwargs):
        if padding is None: padding = ((ks-1)//2 if not transpose else 0)
        bn = norm_type in (NormType.Batch, NormType.BatchZero)
        inn = norm_type in (NormType.Instance, NormType.InstanceZero)
        if bias is None: bias = not (bn or inn)
        conv_func = _conv_func(ndim, transpose=transpose)
        conv = conv_func(ni, nf, kernel_size=ks, bias=bias, stride=stride, padding=padding, **kwargs)
        act = None if act_cls is None else act_cls()
        init_linear(conv, act, init=init, bias_std=bias_std)
        if   norm_type==NormType.Weight:   conv = weight_norm(conv)
        elif norm_type==NormType.Spectral: conv = spectral_norm(conv)
        layers = [conv]
        act_bn = []
        if act is not None: act_bn.append(act)
        if bn: act_bn.append(BatchNorm(nf, norm_type=norm_type, ndim=ndim))
        if inn: act_bn.append(InstanceNorm(nf, norm_type=norm_type, ndim=ndim))
        if bn_1st: act_bn.reverse()
        layers += act_bn
        if xtra: layers.append(xtra)
        super().__init__(*layers)

# %% ../nbs/01_layers.ipynb 77
def AdaptiveAvgPool(sz=1, ndim=2):
    "nn.AdaptiveAvgPool layer for `ndim`"
    assert 1 <= ndim <= 3
    return getattr(nn, f"AdaptiveAvgPool{ndim}d")(sz)

# %% ../nbs/01_layers.ipynb 78
def MaxPool(ks=2, stride=None, padding=0, ndim=2, ceil_mode=False):
    "nn.MaxPool layer for `ndim`"
    assert 1 <= ndim <= 3
    return getattr(nn, f"MaxPool{ndim}d")(ks, stride=stride, padding=padding)

# %% ../nbs/01_layers.ipynb 79
def AvgPool(ks=2, stride=None, padding=0, ndim=2, ceil_mode=False):
    "nn.AvgPool layer for `ndim`"
    assert 1 <= ndim <= 3
    return getattr(nn, f"AvgPool{ndim}d")(ks, stride=stride, padding=padding, ceil_mode=ceil_mode)

# %% ../nbs/01_layers.ipynb 81
def trunc_normal_(x, mean=0., std=1.):
    "Truncated normal initialization (approximation)"
    # From https://discuss.pytorch.org/t/implementing-truncated-normal-initializer/4778/12
    return x.normal_().fmod_(2).mul_(std).add_(mean)

# %% ../nbs/01_layers.ipynb 82
class Embedding(nn.Embedding):
    "Embedding layer with truncated normal initialization"
    def __init__(self, ni, nf, std=0.01):
        super().__init__(ni, nf)
        trunc_normal_(self.weight.data, std=std)

# %% ../nbs/01_layers.ipynb 86
class SelfAttention(Module):
    "Self attention layer for `n_channels`."
    def __init__(self, n_channels):
        self.query,self.key,self.value = [self._conv(n_channels, c) for c in (n_channels//8,n_channels//8,n_channels)]
        self.gamma = nn.Parameter(tensor([0.]))

    def _conv(self,n_in,n_out):
        return ConvLayer(n_in, n_out, ks=1, ndim=1, norm_type=NormType.Spectral, act_cls=None, bias=False)

    def forward(self, x):
        #Notation from the paper.
        size = x.size()
        x = x.view(*size[:2],-1)
        f,g,h = self.query(x),self.key(x),self.value(x)
        beta = F.softmax(torch.bmm(f.transpose(1,2), g), dim=1)
        o = self.gamma * torch.bmm(h, beta) + x
        return o.view(*size).contiguous()

# %% ../nbs/01_layers.ipynb 95
class PooledSelfAttention2d(Module):
    "Pooled self attention layer for 2d."
    def __init__(self, n_channels):
        self.n_channels = n_channels
        self.query,self.key,self.value = [self._conv(n_channels, c) for c in (n_channels//8,n_channels//8,n_channels//2)]
        self.out   = self._conv(n_channels//2, n_channels)
        self.gamma = nn.Parameter(tensor([0.]))

    def _conv(self,n_in,n_out):
        return ConvLayer(n_in, n_out, ks=1, norm_type=NormType.Spectral, act_cls=None, bias=False)

    def forward(self, x):
        n_ftrs = x.shape[2]*x.shape[3]
        f = self.query(x).view(-1, self.n_channels//8, n_ftrs)
        g = F.max_pool2d(self.key(x),   [2,2]).view(-1, self.n_channels//8, n_ftrs//4)
        h = F.max_pool2d(self.value(x), [2,2]).view(-1, self.n_channels//2, n_ftrs//4)
        beta = F.softmax(torch.bmm(f.transpose(1, 2), g), -1)
        o = self.out(torch.bmm(h, beta.transpose(1,2)).view(-1, self.n_channels//2, x.shape[2], x.shape[3]))
        return self.gamma * o + x

# %% ../nbs/01_layers.ipynb 97
def _conv1d_spect(ni:int, no:int, ks:int=1, stride:int=1, padding:int=0, bias:bool=False):
    "Create and initialize a `nn.Conv1d` layer with spectral normalization."
    conv = nn.Conv1d(ni, no, ks, stride=stride, padding=padding, bias=bias)
    nn.init.kaiming_normal_(conv.weight)
    if bias: conv.bias.data.zero_()
    return spectral_norm(conv)

# %% ../nbs/01_layers.ipynb 98
class SimpleSelfAttention(Module):
    def __init__(self, n_in:int, ks=1, sym=False):
        self.sym,self.n_in = sym,n_in
        self.conv = _conv1d_spect(n_in, n_in, ks, padding=ks//2, bias=False)
        self.gamma = nn.Parameter(tensor([0.]))

    def forward(self,x):
        if self.sym:
            c = self.conv.weight.view(self.n_in,self.n_in)
            c = (c + c.t())/2
            self.conv.weight = c.view(self.n_in,self.n_in,1)

        size = x.size()
        x = x.view(*size[:2],-1)

        convx = self.conv(x)
        xxT = torch.bmm(x,x.permute(0,2,1).contiguous())
        o = torch.bmm(xxT, convx)
        o = self.gamma * o + x
        return o.view(*size).contiguous()

# %% ../nbs/01_layers.ipynb 101
def icnr_init(x, scale=2, init=nn.init.kaiming_normal_):
    "ICNR init of `x`, with `scale` and `init` function"
    ni,nf,h,w = x.shape
    ni2 = int(ni/(scale**2))
    k = init(x.new_zeros([ni2,nf,h,w])).transpose(0, 1)
    k = k.contiguous().view(ni2, nf, -1)
    k = k.repeat(1, 1, scale**2)
    return k.contiguous().view([nf,ni,h,w]).transpose(0, 1)

# %% ../nbs/01_layers.ipynb 104
class PixelShuffle_ICNR(nn.Sequential):
    "Upsample by `scale` from `ni` filters to `nf` (default `ni`), using `nn.PixelShuffle`."
    def __init__(self, ni, nf=None, scale=2, blur=False, norm_type=NormType.Weight, act_cls=defaults.activation):
        super().__init__()
        nf = ifnone(nf, ni)
        layers = [ConvLayer(ni, nf*(scale**2), ks=1, norm_type=norm_type, act_cls=act_cls, bias_std=0),
                  nn.PixelShuffle(scale)]
        if norm_type == NormType.Weight:
            layers[0][0].weight_v.data.copy_(icnr_init(layers[0][0].weight_v.data))
            layers[0][0].weight_g.data.copy_(((layers[0][0].weight_v.data**2).sum(dim=[1,2,3])**0.5)[:,None,None,None])
        else:
            layers[0][0].weight.data.copy_(icnr_init(layers[0][0].weight.data))
        if blur: layers += [nn.ReplicationPad2d((1,0,1,0)), nn.AvgPool2d(2, stride=1)]
        super().__init__(*layers)

# %% ../nbs/01_layers.ipynb 110
def sequential(*args):
    "Create an `nn.Sequential`, wrapping items with `Lambda` if needed"
    if len(args) != 1 or not isinstance(args[0], OrderedDict):
        args = list(args)
        for i,o in enumerate(args):
            if not isinstance(o,nn.Module): args[i] = Lambda(o)
    return nn.Sequential(*args)

# %% ../nbs/01_layers.ipynb 111
class SequentialEx(Module):
    "Like `nn.Sequential`, but with ModuleList semantics, and can access module input"
    def __init__(self, *layers): self.layers = nn.ModuleList(layers)

    def forward(self, x):
        res = x
        for l in self.layers:
            res.orig = x
            nres = l(res)
            # We have to remove res.orig to avoid hanging refs and therefore memory leaks
            res.orig, nres.orig = None, None
            res = nres
        return res

    def __getitem__(self,i): return self.layers[i]
    def append(self,l):      return self.layers.append(l)
    def extend(self,l):      return self.layers.extend(l)
    def insert(self,i,l):    return self.layers.insert(i,l)

# %% ../nbs/01_layers.ipynb 113
class MergeLayer(Module):
    "Merge a shortcut with the result of the module by adding them or concatenating them if `dense=True`."
    def __init__(self, dense:bool=False): self.dense=dense
    def forward(self, x): return torch.cat([x,x.orig], dim=1) if self.dense else (x+x.orig)

# %% ../nbs/01_layers.ipynb 118
class Cat(nn.ModuleList):
    "Concatenate layers outputs over a given dim"
    def __init__(self, layers, dim=1):
        self.dim=dim
        super().__init__(layers)
    def forward(self, x): return torch.cat([l(x) for l in self], dim=self.dim)

# %% ../nbs/01_layers.ipynb 121
class SimpleCNN(nn.Sequential):
    "Create a simple CNN with `filters`."
    def __init__(self, filters, kernel_szs=None, strides=None, bn=True):
        nl = len(filters)-1
        kernel_szs = ifnone(kernel_szs, [3]*nl)
        strides    = ifnone(strides   , [2]*nl)
        layers = [ConvLayer(filters[i], filters[i+1], kernel_szs[i], stride=strides[i],
                  norm_type=(NormType.Batch if bn and i<nl-1 else None)) for i in range(nl)]
        layers.append(PoolFlatten())
        super().__init__(*layers)

# %% ../nbs/01_layers.ipynb 128
class ProdLayer(Module):
    "Merge a shortcut with the result of the module by multiplying them."
    def forward(self, x): return x * x.orig

# %% ../nbs/01_layers.ipynb 129
inplace_relu = partial(nn.ReLU, inplace=True)

# %% ../nbs/01_layers.ipynb 130
def SEModule(ch, reduction, act_cls=defaults.activation):
    nf = math.ceil(ch//reduction/8)*8
    return SequentialEx(nn.AdaptiveAvgPool2d(1),
                        ConvLayer(ch, nf, ks=1, norm_type=None, act_cls=act_cls),
                        ConvLayer(nf, ch, ks=1, norm_type=None, act_cls=nn.Sigmoid),
                        ProdLayer())

# %% ../nbs/01_layers.ipynb 131
class ResBlock(Module):
    "Resnet block from `ni` to `nh` with `stride`"
    @delegates(ConvLayer.__init__)
    def __init__(self, expansion, ni, nf, stride=1, groups=1, reduction=None, nh1=None, nh2=None, dw=False, g2=1,
                 sa=False, sym=False, norm_type=NormType.Batch, act_cls=defaults.activation, ndim=2, ks=3,
                 pool=AvgPool, pool_first=True, **kwargs):
        norm2 = (NormType.BatchZero if norm_type==NormType.Batch else
                 NormType.InstanceZero if norm_type==NormType.Instance else norm_type)
        if nh2 is None: nh2 = nf
        if nh1 is None: nh1 = nh2
        nf,ni = nf*expansion,ni*expansion
        k0 = dict(norm_type=norm_type, act_cls=act_cls, ndim=ndim, **kwargs)
        k1 = dict(norm_type=norm2, act_cls=None, ndim=ndim, **kwargs)
        convpath  = [ConvLayer(ni,  nh2, ks, stride=stride, groups=ni if dw else groups, **k0),
                     ConvLayer(nh2,  nf, ks, groups=g2, **k1)
        ] if expansion == 1 else [
                     ConvLayer(ni,  nh1, 1, **k0),
                     ConvLayer(nh1, nh2, ks, stride=stride, groups=nh1 if dw else groups, **k0),
                     ConvLayer(nh2,  nf, 1, groups=g2, **k1)]
        if reduction: convpath.append(SEModule(nf, reduction=reduction, act_cls=act_cls))
        if sa: convpath.append(SimpleSelfAttention(nf,ks=1,sym=sym))
        self.convpath = nn.Sequential(*convpath)
        idpath = []
        if ni!=nf: idpath.append(ConvLayer(ni, nf, 1, act_cls=None, ndim=ndim, **kwargs))
        if stride!=1: idpath.insert((1,0)[pool_first], pool(stride, ndim=ndim, ceil_mode=True))
        self.idpath = nn.Sequential(*idpath)
        self.act = defaults.activation(inplace=True) if act_cls is defaults.activation else act_cls()

    def forward(self, x): return self.act(self.convpath(x) + self.idpath(x))

# %% ../nbs/01_layers.ipynb 133
def SEBlock(expansion, ni, nf, groups=1, reduction=16, stride=1, **kwargs):
    return ResBlock(expansion, ni, nf, stride=stride, groups=groups, reduction=reduction, nh1=nf*2, nh2=nf*expansion, **kwargs)

# %% ../nbs/01_layers.ipynb 134
def SEResNeXtBlock(expansion, ni, nf, groups=32, reduction=16, stride=1, base_width=4, **kwargs):
    w = math.floor(nf * (base_width / 64)) * groups
    return ResBlock(expansion, ni, nf, stride=stride, groups=groups, reduction=reduction, nh2=w, **kwargs)

# %% ../nbs/01_layers.ipynb 135
def SeparableBlock(expansion, ni, nf, reduction=16, stride=1, base_width=4, **kwargs):
    return ResBlock(expansion, ni, nf, stride=stride, reduction=reduction, nh2=nf*2, dw=True, **kwargs)

# %% ../nbs/01_layers.ipynb 138
def _stack_tups(tuples, stack_dim=1):
    "Stack tuple of tensors along `stack_dim`"
    return tuple(torch.stack([t[i] for t in tuples], dim=stack_dim) for i in range_of(tuples[0]))

# %% ../nbs/01_layers.ipynb 139
class TimeDistributed(Module):
    "Applies `module` over `tdim` identically for each step, use `low_mem` to compute one at a time." 
    def __init__(self, module, low_mem=False, tdim=1):
        store_attr()
        
    def forward(self, *tensors, **kwargs):
        "input x with shape:(bs,seq_len,channels,width,height)"
        if self.low_mem or self.tdim!=1: 
            return self.low_mem_forward(*tensors, **kwargs)
        else:
            #only support tdim=1
            inp_shape = tensors[0].shape
            bs, seq_len = inp_shape[0], inp_shape[1]   
            out = self.module(*[x.view(bs*seq_len, *x.shape[2:]) for x in tensors], **kwargs)
        return self.format_output(out, bs, seq_len)
    
    def low_mem_forward(self, *tensors, **kwargs):                                           
        "input x with shape:(bs,seq_len,channels,width,height)"
        seq_len = tensors[0].shape[self.tdim]
        args_split = [torch.unbind(x, dim=self.tdim) for x in tensors]
        out = []
        for i in range(seq_len):
            out.append(self.module(*[args[i] for args in args_split]), **kwargs)
        if isinstance(out[0], tuple):
            return _stack_tups(out, stack_dim=self.tdim)
        return torch.stack(out, dim=self.tdim)
    
    def format_output(self, out, bs, seq_len):
        "unstack from batchsize outputs"
        if isinstance(out, tuple):
            return tuple(out_i.view(bs, seq_len, *out_i.shape[1:]) for out_i in out)
        return out.view(bs, seq_len,*out.shape[1:])
    
    def __repr__(self):
        return f'TimeDistributed({self.module})'

# %% ../nbs/01_layers.ipynb 158
from torch.jit import script

# %% ../nbs/01_layers.ipynb 159
@script
def _swish_jit_fwd(x): return x.mul(torch.sigmoid(x))

@script
def _swish_jit_bwd(x, grad_output):
    x_sigmoid = torch.sigmoid(x)
    return grad_output * (x_sigmoid * (1 + x * (1 - x_sigmoid)))

class _SwishJitAutoFn(torch.autograd.Function):
    @staticmethod
    def forward(ctx, x):
        ctx.save_for_backward(x)
        return _swish_jit_fwd(x)

    @staticmethod
    def backward(ctx, grad_output):
        x = ctx.saved_variables[0]
        return _swish_jit_bwd(x, grad_output)

# %% ../nbs/01_layers.ipynb 160
def swish(x, inplace=False): F.silu(x, inplace=inplace)

# %% ../nbs/01_layers.ipynb 161
class SwishJit(Module):
    def forward(self, x): return _SwishJitAutoFn.apply(x)

# %% ../nbs/01_layers.ipynb 162
@script
def _mish_jit_fwd(x): return x.mul(torch.tanh(F.softplus(x)))

@script
def _mish_jit_bwd(x, grad_output):
    x_sigmoid = torch.sigmoid(x)
    x_tanh_sp = F.softplus(x).tanh()
    return grad_output.mul(x_tanh_sp + x * x_sigmoid * (1 - x_tanh_sp * x_tanh_sp))

class MishJitAutoFn(torch.autograd.Function):
    @staticmethod
    def forward(ctx, x):
        ctx.save_for_backward(x)
        return _mish_jit_fwd(x)

    @staticmethod
    def backward(ctx, grad_output):
        x = ctx.saved_variables[0]
        return _mish_jit_bwd(x, grad_output)

# %% ../nbs/01_layers.ipynb 163
def mish(x, inplace=False): return F.mish(x, inplace=inplace)

# %% ../nbs/01_layers.ipynb 164
class MishJit(Module):
    def forward(self, x): return MishJitAutoFn.apply(x)

# %% ../nbs/01_layers.ipynb 165
Mish = nn.Mish
Swish = nn.SiLU

# %% ../nbs/01_layers.ipynb 166
for o in swish,Swish,SwishJit,mish,Mish,MishJit: o.__default_init__ = kaiming_uniform_

# %% ../nbs/01_layers.ipynb 169
class ParameterModule(Module):
    "Register a lone parameter `p` in a module."
    def __init__(self, p): self.val = p
    def forward(self, x): return x

# %% ../nbs/01_layers.ipynb 170
def children_and_parameters(m):
    "Return the children of `m` and its direct parameters not registered in modules."
    children = list(m.children())
    children_p = sum([[id(p) for p in c.parameters()] for c in m.children()],[])
    for p in m.parameters():
        if id(p) not in children_p: children.append(ParameterModule(p))
    return children

# %% ../nbs/01_layers.ipynb 172
def has_children(m):
    try: next(m.children())
    except StopIteration: return False
    return True

# %% ../nbs/01_layers.ipynb 174
def flatten_model(m):
    "Return the list of all submodules and parameters of `m`"
    return sum(map(flatten_model,children_and_parameters(m)),[]) if has_children(m) else [m]

# %% ../nbs/01_layers.ipynb 176
class NoneReduce():
    "A context manager to evaluate `loss_func` with none reduce."
    def __init__(self, loss_func): self.loss_func,self.old_red = loss_func,None

    def __enter__(self):
        if hasattr(self.loss_func, 'reduction'):
            self.old_red = self.loss_func.reduction
            self.loss_func.reduction = 'none'
            return self.loss_func
        else: return partial(self.loss_func, reduction='none')

    def __exit__(self, type, value, traceback):
        if self.old_red is not None: self.loss_func.reduction = self.old_red

# %% ../nbs/01_layers.ipynb 178
def in_channels(m):
    "Return the shape of the first weight layer in `m`."
    try: return next(l.weight.shape[1] for l in flatten_model(m) if nested_attr(l,'weight.ndim',-1)==4)
    except StopIteration as e: e.args = ["No weight layer"]; raise