allow loading custom weights files for EfficientNet

Author: IanButterworth

src/convnets/efficientnets/efficientnet.jl

@@ -60,20 +60,21 @@ function efficientnet(config::Symbol; norm_layer = BatchNorm, stochastic_depth_p
 end
 
 """
-    EfficientNet(config::Symbol; pretrain::Bool = false, inchannels::Integer = 3,
+    EfficientNet(config::Symbol; pretrain::Union{Bool,String} = false, inchannels::Integer = 3,
                  nclasses::Integer = 1000)
 
 Create an EfficientNet model ([reference](https://arxiv.org/abs/1905.11946v5)).
 
 # Arguments
 
   - `config`: size of the model. Can be one of `[:b0, :b1, :b2, :b3, :b4, :b5, :b6, :b7, :b8]`.
-  - `pretrain`: set to `true` to load the pre-trained weights for ImageNet
+  - `pretrain`: set to `true` to load the pre-trained weights for ImageNet, or provide a local path string to load a
+                custom weights file.
   - `inchannels`: number of input channels.
   - `nclasses`: number of output classes.
 
 !!! warning
-    
+
     EfficientNet does not currently support pretrained weights.
 
 See also [`Metalhead.efficientnet`](@ref).
@@ -83,12 +84,16 @@ struct EfficientNet
 end
 @functor EfficientNet
 
-function EfficientNet(config::Symbol; pretrain::Bool = false, inchannels::Integer = 3,
+function EfficientNet(config::Symbol; pretrain::Union{Bool,String} = false, inchannels::Integer = 3,
                       nclasses::Integer = 1000)
     layers = efficientnet(config; inchannels, nclasses)
     model = EfficientNet(layers)
-    if pretrain
+    if pretrain === true
         loadpretrain!(model, string("efficientnet_", config))
+    elseif pretrain isa String
+        isfile(pretrain) || error("Weights file does not exist at `$pretrain`")
+        m = load_weights_file(pretrain)
+        Flux.loadmodel!(model, m)
     end
     return model
 end

src/pretrain.jl

@@ -5,7 +5,7 @@ Load the pre-trained weights for `model` using the stored artifacts.
 """
 function loadweights(artifact_name)
     artifact_dir = try
-        @artifact_str(artifact_name)   
+        @artifact_str(artifact_name)
     catch e
         throw(ArgumentError("No pre-trained weights available for $artifact_name."))
     end
@@ -23,15 +23,19 @@ function loadweights(artifact_name)
     end
 
     file_path = joinpath(artifact_dir, file_name)
-    
-    if endswith(file_name, ".bson")
+
+    return load_weights_file(file_path)
+end
+
+function load_weights_file(file_path::String)
+    if endswith(file_path, ".bson")
         artifact = BSON.load(file_path, @__MODULE__)
         if haskey(artifact, :model_state)
             return artifact[:model_state]
         elseif haskey(artifact, :model)
             return artifact[:model]
         else
-            throw(ErrorException("Found weight artifact for $artifact_name but the weights are not saved under the key :model_state or :model."))
+            throw(ErrorException("Weights in the file `$file_path` are not saved under the key :model_state or :model."))
         end
     elseif endswith(file_path, ".jld2")
         artifact = JLD2.load(file_path)
@@ -40,10 +44,10 @@ function loadweights(artifact_name)
         elseif haskey(artifact, "model")
             return artifact["model"]
         else
-            throw(ErrorException("Found weight artifact for $artifact_name but the weights are not saved under the key \"model_state\" or \"model\"."))
+            throw(ErrorException("Weights in the file `$file_path` are not saved under the key \"model_state\" or \"model\"."))
         end
     else
-        throw(ErrorException("Found weight artifact for $artifact_name but only jld2 and bson serialization format are supported."))
+        throw(ErrorException("Only jld2 and bson serialization format are supported for weights files."))
     end
 end