Added typing annotations to models/segmentation (#4227)

* style: Added typing annotations to segmentation/_utils

* style: Added typing annotations to segmentation/segmentation

* style: Added typing annotations to remaining segmentation models

* style: Fixed typing of DeepLab

* style: Fixed typing

* fix: Fixed typing annotations & default values

* Fixing python_type_check

torchvision/models/segmentation/_utils.py

 from collections import OrderedDict
+from typing import Optional, Dict
 
-from torch import nn
+from torch import nn, Tensor
 from torch.nn import functional as F
 
 
 class _SimpleSegmentationModel(nn.Module):
     __constants__ = ['aux_classifier']
 
-    def __init__(self, backbone, classifier, aux_classifier=None):
+    def __init__(
+        self,
+        backbone: nn.Module,
+        classifier: nn.Module,
+        aux_classifier: Optional[nn.Module] = None
+    ) -> None:
         super(_SimpleSegmentationModel, self).__init__()
         self.backbone = backbone
         self.classifier = classifier
         self.aux_classifier = aux_classifier
 
-    def forward(self, x):
+    def forward(self, x: Tensor) -> Dict[str, Tensor]:
         input_shape = x.shape[-2:]
         # contract: features is a dict of tensors
         features = self.backbone(x)

torchvision/models/segmentation/deeplabv3.py

 import torch
 from torch import nn
 from torch.nn import functional as F
+from typing import List
 
 from ._utils import _SimpleSegmentationModel
 
@@ -27,7 +28,7 @@ class DeepLabV3(_SimpleSegmentationModel):
 
 
 class DeepLabHead(nn.Sequential):
-    def __init__(self, in_channels, num_classes):
+    def __init__(self, in_channels: int, num_classes: int) -> None:
         super(DeepLabHead, self).__init__(
             ASPP(in_channels, [12, 24, 36]),
             nn.Conv2d(256, 256, 3, padding=1, bias=False),
@@ -38,7 +39,7 @@ class DeepLabHead(nn.Sequential):
 
 
 class ASPPConv(nn.Sequential):
-    def __init__(self, in_channels, out_channels, dilation):
+    def __init__(self, in_channels: int, out_channels: int, dilation: int) -> None:
         modules = [
             nn.Conv2d(in_channels, out_channels, 3, padding=dilation, dilation=dilation, bias=False),
             nn.BatchNorm2d(out_channels),
@@ -48,14 +49,14 @@ class ASPPConv(nn.Sequential):
 
 
 class ASPPPooling(nn.Sequential):
-    def __init__(self, in_channels, out_channels):
+    def __init__(self, in_channels: int, out_channels: int) -> None:
         super(ASPPPooling, self).__init__(
             nn.AdaptiveAvgPool2d(1),
             nn.Conv2d(in_channels, out_channels, 1, bias=False),
             nn.BatchNorm2d(out_channels),
             nn.ReLU())
 
-    def forward(self, x):
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
         size = x.shape[-2:]
         for mod in self:
             x = mod(x)
@@ -63,7 +64,7 @@ class ASPPPooling(nn.Sequential):
 
 
 class ASPP(nn.Module):
-    def __init__(self, in_channels, atrous_rates, out_channels=256):
+    def __init__(self, in_channels: int, atrous_rates: List[int], out_channels: int = 256) -> None:
         super(ASPP, self).__init__()
         modules = []
         modules.append(nn.Sequential(
@@ -85,9 +86,9 @@ class ASPP(nn.Module):
             nn.ReLU(),
             nn.Dropout(0.5))
 
-    def forward(self, x):
-        res = []
+    def forward(self, x: torch.Tensor) -> torch.Tensor:
+        _res = []
         for conv in self.convs:
-            res.append(conv(x))
-        res = torch.cat(res, dim=1)
+            _res.append(conv(x))
+        res = torch.cat(_res, dim=1)
         return self.project(res)

torchvision/models/segmentation/fcn.py

@@ -23,7 +23,7 @@ class FCN(_SimpleSegmentationModel):
 
 
 class FCNHead(nn.Sequential):
-    def __init__(self, in_channels, channels):
+    def __init__(self, in_channels: int, channels: int) -> None:
         inter_channels = in_channels // 4
         layers = [
             nn.Conv2d(in_channels, inter_channels, 3, padding=1, bias=False),

torchvision/models/segmentation/lraspp.py

@@ -24,12 +24,19 @@ class LRASPP(nn.Module):
         inter_channels (int, optional): the number of channels for intermediate computations.
     """
 
-    def __init__(self, backbone, low_channels, high_channels, num_classes, inter_channels=128):
+    def __init__(
+        self,
+        backbone: nn.Module,
+        low_channels: int,
+        high_channels: int,
+        num_classes: int,
+        inter_channels: int = 128
+    ) -> None:
         super().__init__()
         self.backbone = backbone
         self.classifier = LRASPPHead(low_channels, high_channels, num_classes, inter_channels)
 
-    def forward(self, input):
+    def forward(self, input: Tensor) -> Dict[str, Tensor]:
         features = self.backbone(input)
         out = self.classifier(features)
         out = F.interpolate(out, size=input.shape[-2:], mode='bilinear', align_corners=False)
@@ -42,7 +49,13 @@ class LRASPP(nn.Module):
 
 class LRASPPHead(nn.Module):
 
-    def __init__(self, low_channels, high_channels, num_classes, inter_channels):
+    def __init__(
+        self,
+        low_channels: int,
+        high_channels: int,
+        num_classes: int,
+        inter_channels: int
+    ) -> None:
         super().__init__()
         self.cbr = nn.Sequential(
             nn.Conv2d(high_channels, inter_channels, 1, bias=False),

torchvision/models/segmentation/segmentation.py

+from torch import nn
+from typing import Any, Optional
 from .._utils import IntermediateLayerGetter
 from ..._internally_replaced_utils import load_state_dict_from_url
 from .. import mobilenetv3
@@ -22,7 +24,13 @@ model_urls = {
 }
 
 
-def _segm_model(name, backbone_name, num_classes, aux, pretrained_backbone=True):
+def _segm_model(
+    name: str,
+    backbone_name: str,
+    num_classes: int,
+    aux: Optional[bool],
+    pretrained_backbone: bool = True
+) -> nn.Module:
     if 'resnet' in backbone_name:
         backbone = resnet.__dict__[backbone_name](
             pretrained=pretrained_backbone,
@@ -66,7 +74,15 @@ def _segm_model(name, backbone_name, num_classes, aux, pretrained_backbone=True)
     return model
 
 
-def _load_model(arch_type, backbone, pretrained, progress, num_classes, aux_loss, **kwargs):
+def _load_model(
+    arch_type: str,
+    backbone: str,
+    pretrained: bool,
+    progress: bool,
+    num_classes: int,
+    aux_loss: Optional[bool],
+    **kwargs: Any
+) -> nn.Module:
     if pretrained:
         aux_loss = True
         kwargs["pretrained_backbone"] = False
@@ -76,7 +92,7 @@ def _load_model(arch_type, backbone, pretrained, progress, num_classes, aux_loss
     return model
 
 
-def _load_weights(model, arch_type, backbone, progress):
+def _load_weights(model: nn.Module, arch_type: str, backbone: str, progress: bool) -> None:
     arch = arch_type + '_' + backbone + '_coco'
     model_url = model_urls.get(arch, None)
     if model_url is None:
@@ -86,7 +102,7 @@ def _load_weights(model, arch_type, backbone, progress):
         model.load_state_dict(state_dict)
 
 
-def _segm_lraspp_mobilenetv3(backbone_name, num_classes, pretrained_backbone=True):
+def _segm_lraspp_mobilenetv3(backbone_name: str, num_classes: int, pretrained_backbone: bool = True) -> LRASPP:
     backbone = mobilenetv3.__dict__[backbone_name](pretrained=pretrained_backbone, dilated=True).features
 
     # Gather the indices of blocks which are strided. These are the locations of C1, ..., Cn-1 blocks.
@@ -103,8 +119,13 @@ def _segm_lraspp_mobilenetv3(backbone_name, num_classes, pretrained_backbone=Tru
     return model
 
 
-def fcn_resnet50(pretrained=False, progress=True,
-                 num_classes=21, aux_loss=None, **kwargs):
+def fcn_resnet50(
+    pretrained: bool = False,
+    progress: bool = True,
+    num_classes: int = 21,
+    aux_loss: Optional[bool] = None,
+    **kwargs: Any
+) -> nn.Module:
     """Constructs a Fully-Convolutional Network model with a ResNet-50 backbone.
 
     Args:
@@ -117,8 +138,13 @@ def fcn_resnet50(pretrained=False, progress=True,
     return _load_model('fcn', 'resnet50', pretrained, progress, num_classes, aux_loss, **kwargs)
 
 
-def fcn_resnet101(pretrained=False, progress=True,
-                  num_classes=21, aux_loss=None, **kwargs):
+def fcn_resnet101(
+    pretrained: bool = False,
+    progress: bool = True,
+    num_classes: int = 21,
+    aux_loss: Optional[bool] = None,
+    **kwargs: Any
+) -> nn.Module:
     """Constructs a Fully-Convolutional Network model with a ResNet-101 backbone.
 
     Args:
@@ -131,8 +157,13 @@ def fcn_resnet101(pretrained=False, progress=True,
     return _load_model('fcn', 'resnet101', pretrained, progress, num_classes, aux_loss, **kwargs)
 
 
-def deeplabv3_resnet50(pretrained=False, progress=True,
-                       num_classes=21, aux_loss=None, **kwargs):
+def deeplabv3_resnet50(
+    pretrained: bool = False,
+    progress: bool = True,
+    num_classes: int = 21,
+    aux_loss: Optional[bool] = None,
+    **kwargs: Any
+) -> nn.Module:
     """Constructs a DeepLabV3 model with a ResNet-50 backbone.
 
     Args:
@@ -145,8 +176,13 @@ def deeplabv3_resnet50(pretrained=False, progress=True,
     return _load_model('deeplabv3', 'resnet50', pretrained, progress, num_classes, aux_loss, **kwargs)
 
 
-def deeplabv3_resnet101(pretrained=False, progress=True,
-                        num_classes=21, aux_loss=None, **kwargs):
+def deeplabv3_resnet101(
+    pretrained: bool = False,
+    progress: bool = True,
+    num_classes: int = 21,
+    aux_loss: Optional[bool] = None,
+    **kwargs: Any
+) -> nn.Module:
     """Constructs a DeepLabV3 model with a ResNet-101 backbone.
 
     Args:
@@ -159,8 +195,13 @@ def deeplabv3_resnet101(pretrained=False, progress=True,
     return _load_model('deeplabv3', 'resnet101', pretrained, progress, num_classes, aux_loss, **kwargs)
 
 
-def deeplabv3_mobilenet_v3_large(pretrained=False, progress=True,
-                                 num_classes=21, aux_loss=None, **kwargs):
+def deeplabv3_mobilenet_v3_large(
+    pretrained: bool = False,
+    progress: bool = True,
+    num_classes: int = 21,
+    aux_loss: Optional[bool] = None,
+    **kwargs: Any
+) -> nn.Module:
     """Constructs a DeepLabV3 model with a MobileNetV3-Large backbone.
 
     Args:
@@ -173,7 +214,12 @@ def deeplabv3_mobilenet_v3_large(pretrained=False, progress=True,
     return _load_model('deeplabv3', 'mobilenet_v3_large', pretrained, progress, num_classes, aux_loss, **kwargs)
 
 
-def lraspp_mobilenet_v3_large(pretrained=False, progress=True, num_classes=21, **kwargs):
+def lraspp_mobilenet_v3_large(
+    pretrained: bool = False,
+    progress: bool = True,
+    num_classes: int = 21,
+    **kwargs: Any
+) -> nn.Module:
     """Constructs a Lite R-ASPP Network model with a MobileNetV3-Large backbone.
 
     Args: