FIX cache_or_load_file method And load mnist

lib/chainer/dataset/download.rb

@@ -34,15 +34,22 @@ def self.get_dataset_directory(dataset_name, create_directory: true)
         path
       end
 
-      def self.cache_or_load_file(path, data)
-        return PStore.new(path).transaction { |t| t['data'] } if File.exist?(path)
+      def self.cache_or_load_file(path, &creator)
+        raise 'Please set dataset creator on block' if creator.nil?
 
-        pstore = PStore.new(path)
-        pstore.transaction{|t|
-          t["data"] = data
-        }
+        return PStore.new(path).transaction { |t| t['data'] } if File.exist?(path)
 
+        data = creator.call
+        PStore.new(path).transaction do |t|
+          t['data'] = data
+        end
         data
+      rescue TypeError => e
+        puts e.message
+        FileUtils.rm_f(path)
+        cache_or_load_file(path) do
+          creator.call
+        end
       end
     end
   end

lib/chainer/datasets/mnist.rb

@@ -48,8 +48,9 @@ def self.retrieve_mnist_test
       def self.retrieve_mnist(name, urls)
         root = Chainer::Dataset::Download.get_dataset_directory('pfnet/chainer/mnist')
         path = File.expand_path(name, root)
-        creator = make_npz(path, urls)
-        Chainer::Dataset::Download.cache_or_load_file(path, creator)
+        Chainer::Dataset::Download.cache_or_load_file(path) do
+          make_npz(path, urls)
+        end
       end
 
       def self.make_npz(path, urls)