prompt: We are currently solving the following issue within our repository. Here is the issue text:
  --- BEGIN ISSUE ---
  Create encoding preprocessors not until runtime
  Right now the preprocessors are created at import
  
  https://github.com/pmeier/pystiche/blob/cad5ab6e9485680f2543cf4397d0d21e72a88b9e/pystiche/enc/preprocessing.py#L1-L4
  
  We should only create them if they are needed to speed up the import.
  
  --- END ISSUE ---
  
  Below are some code segments, each from a relevant file. One or more of these files may contain bugs.
  --- BEGIN FILES ---
  Path: `pystiche/enc/preprocessing.py`
  Content:
  ```
  1 from torch import nn
  2 from pystiche.image import TorchPreprocessing, CaffePreprocessing
  3 
  4 PREPROCESSORS = {"torch": TorchPreprocessing(), "caffe": CaffePreprocessing()}
  5 
  6 __all__ = ["get_preprocessor"]
  7 
  8 
  9 def get_preprocessor(framework: str) -> nn.Module:
  10     return PREPROCESSORS[framework]
  11
  ```
  --- END FILES ---
  
  Please first localize the bug based on the issue statement, and then generate a patch according to the `git diff` format fenced by three backticks.
  
  Here is an example:
  
  ```diff
  diff --git a/examples/server_async.py b/examples/server_async.py
  --- a/examples/server_async.py
  +++ b/examples/server_async.py
  @@ -313,4 +313,4 @@
   
   
   if __name__ == "__main__":
  -    asyncio.run(run_async_server("."), debug=True)
  +    asyncio.run(run_async_server(), debug=True)
  diff --git a/examples/server_sync.py b/examples/server_sync.py
  --- a/examples/server_sync.py
  +++ b/examples/server_sync.py
  @@ -313,5 +313,5 @@
   
   
   if __name__ == "__main__":
  -    server = run_sync_server(".")
  +    server = run_sync_server()
       server.shutdown()
  
  ```
  
golden_diff: diff --git a/pystiche/enc/preprocessing.py b/pystiche/enc/preprocessing.py
  --- a/pystiche/enc/preprocessing.py
  +++ b/pystiche/enc/preprocessing.py
  @@ -1,10 +1,10 @@
   from torch import nn
   from pystiche.image import TorchPreprocessing, CaffePreprocessing
   
  -PREPROCESSORS = {"torch": TorchPreprocessing(), "caffe": CaffePreprocessing()}
  +PREPROCESSORS = {"torch": TorchPreprocessing, "caffe": CaffePreprocessing}
   
   __all__ = ["get_preprocessor"]
   
   
   def get_preprocessor(framework: str) -> nn.Module:
  -    return PREPROCESSORS[framework]
  +    return PREPROCESSORS[framework]()
  
verification_info: {"golden_diff": "diff --git a/pystiche/enc/preprocessing.py b/pystiche/enc/preprocessing.py\n--- a/pystiche/enc/preprocessing.py\n+++ b/pystiche/enc/preprocessing.py\n@@ -1,10 +1,10 @@\n from torch import nn\n from pystiche.image import TorchPreprocessing, CaffePreprocessing\n \n-PREPROCESSORS = {\"torch\": TorchPreprocessing(), \"caffe\": CaffePreprocessing()}\n+PREPROCESSORS = {\"torch\": TorchPreprocessing, \"caffe\": CaffePreprocessing}\n \n __all__ = [\"get_preprocessor\"]\n \n \n def get_preprocessor(framework: str) -> nn.Module:\n-    return PREPROCESSORS[framework]\n+    return PREPROCESSORS[framework]()\n", "issue": "Create encoding preprocessors not until runtime\nRight now the preprocessors are created at import\r\n\r\nhttps://github.com/pmeier/pystiche/blob/cad5ab6e9485680f2543cf4397d0d21e72a88b9e/pystiche/enc/preprocessing.py#L1-L4\r\n\r\nWe should only create them if they are needed to speed up the import.\n", "before_files": [{"content": "from torch import nn\nfrom pystiche.image import TorchPreprocessing, CaffePreprocessing\n\nPREPROCESSORS = {\"torch\": TorchPreprocessing(), \"caffe\": CaffePreprocessing()}\n\n__all__ = [\"get_preprocessor\"]\n\n\ndef get_preprocessor(framework: str) -> nn.Module:\n    return PREPROCESSORS[framework]\n", "path": "pystiche/enc/preprocessing.py"}], "after_files": [{"content": "from torch import nn\nfrom pystiche.image import TorchPreprocessing, CaffePreprocessing\n\nPREPROCESSORS = {\"torch\": TorchPreprocessing, \"caffe\": CaffePreprocessing}\n\n__all__ = [\"get_preprocessor\"]\n\n\ndef get_preprocessor(framework: str) -> nn.Module:\n    return PREPROCESSORS[framework]()\n", "path": "pystiche/enc/preprocessing.py"}]}