use some magic just this once to remove the need for researchers to think

README.md

@@ -218,7 +218,6 @@ unet1 = Unet(
 unet2 = Unet(
     dim = 16,
     image_embed_dim = 512,
-    lowres_cond = True,         # subsequent unets must have this turned on (and first unet must have this turned off)
     cond_dim = 128,
     channels = 3,
     dim_mults = (1, 2, 4, 8, 16)
@@ -349,8 +348,7 @@ unet2 = Unet(
     image_embed_dim = 512,
     cond_dim = 128,
     channels = 3,
-    dim_mults = (1, 2, 4, 8, 16),
-    lowres_cond = True
+    dim_mults = (1, 2, 4, 8, 16)
 ).cuda()
 
 decoder = Decoder(

dalle2_pytorch/dalle2_pytorch.py

@@ -816,6 +816,11 @@ class Unet(nn.Module):
         attend_at_middle = True, # whether to have a layer of attention at the bottleneck (can turn off for higher resolution in cascading DDPM, before bringing in efficient attention)
     ):
         super().__init__()
+        # save locals to take care of some hyperparameters for cascading DDPM
+
+        self._locals = locals()
+        del self._locals['self']
+        del self._locals['__class__']
 
         # for eventual cascading diffusion
 
@@ -896,6 +901,15 @@ class Unet(nn.Module):
             nn.Conv2d(dim, out_dim, 1)
         )
 
+    # if the current settings for the unet are not correct
+    # for cascading DDPM, then reinit the unet with the right settings
+    def force_lowres_cond(self, lowres_cond):
+        if lowres_cond == self.lowres_cond:
+            return self
+
+        updated_kwargs = {**self._locals, 'lowres_cond': lowres_cond}
+        return self.__class__(**updated_kwargs)
+
     def forward_with_cond_scale(
         self,
         *args,
@@ -1021,7 +1035,17 @@ class Decoder(nn.Module):
         self.clip_image_size = clip.image_size
         self.channels = clip.image_channels
 
-        self.unets = nn.ModuleList(unet)
+        # automatically take care of ensuring that first unet is unconditional
+        # while the rest of the unets are conditioned on the low resolution image produced by previous unet
+
+        self.unets = nn.ModuleList([])
+        for ind, one_unet in enumerate(cast_tuple(unet)):
+            is_first = ind == 0
+            one_unet = one_unet.force_lowres_cond(not is_first)
+            self.unets.append(one_unet)
+
+        # unet image sizes
+
         image_sizes = default(image_sizes, (clip.image_size,))
         image_sizes = tuple(sorted(set(image_sizes)))
 

setup.py

@@ -10,7 +10,7 @@ setup(
       'dream = dalle2_pytorch.cli:dream'
     ],
   },
-  version = '0.0.21',
+  version = '0.0.22',
   license='MIT',
   description = 'DALL-E 2',
   author = 'Phil Wang',