STAR-322: Fixing style errors

plugins/UM3NetworkPrinting/src/MeshFormatHandler.py

@@ -1,7 +1,7 @@
 # Copyright (c) 2018 Ultimaker B.V.
 # Cura is released under the terms of the LGPLv3 or higher.
 import io
-from typing import Optional, Dict, Union, List
+from typing import Optional, Dict, Union, List, cast
 
 from UM.FileHandler.FileHandler import FileHandler
 from UM.FileHandler.FileWriter import FileWriter
@@ -26,7 +26,7 @@ class MeshFormatHandler:
     def __init__(self, file_handler: Optional[FileHandler], firmware_version: str) -> None:
         self._file_handler = file_handler or CuraApplication.getInstance().getMeshFileHandler()
         self._preferred_format = self._getPreferredFormat(firmware_version)
-        self._writer = self._getWriter(self._preferred_format["mime_type"]) if self._preferred_format else None
+        self._writer = self._getWriter(self.mime_type) if self._preferred_format else None
 
     @property
     def is_valid(self) -> bool:
@@ -47,32 +47,40 @@ class MeshFormatHandler:
 
     @property
     def mime_type(self) -> str:
-        return self._preferred_format["mime_type"]
+        return cast(str, self._preferred_format["mime_type"])
 
     ## Gets the file mode (FileWriter.OutputMode.TextMode or FileWriter.OutputMode.BinaryMode)
     @property
     def file_mode(self) -> int:
-        return self._preferred_format["mode"]
+        return cast(int, self._preferred_format["mode"])
 
     ## Gets the file extension
     @property
     def file_extension(self) -> str:
-        return self._preferred_format["extension"]
+        return cast(str, self._preferred_format["extension"])
 
     ## Creates the right kind of stream based on the preferred format.
     def createStream(self) -> Union[io.BytesIO, io.StringIO]:
-        return io.StringIO() if self.file_mode == FileWriter.OutputMode.TextMode else io.BytesIO()
+        if self.file_mode == FileWriter.OutputMode.TextMode:
+            return io.StringIO()
+        else:
+            return io.BytesIO()
 
     ## Writes the mesh and returns its value.
     def getBytes(self, nodes: List[SceneNode]) -> bytes:
+        if self.writer is None:
+            raise ValueError("There is no writer for the mesh format handler.")
         stream = self.createStream()
         self.writer.write(stream, nodes)
-        return stream.getvalue()
+        value = stream.getvalue()
+        if isinstance(value, str):
+            value = value.encode()
+        return value
 
     ## Chooses the preferred file format for the given file handler.
     #  \param firmware_version: The version of the firmware.
     #  \return A dict with the file format details.
-    def _getPreferredFormat(self, firmware_version: str) -> Optional[Dict[str, Union[str, int, bool]]]:
+    def _getPreferredFormat(self, firmware_version: str) -> Dict[str, Union[str, int, bool]]:
         # Formats supported by this application (file types that we can actually write).
         application = CuraApplication.getInstance()
 
@@ -82,7 +90,7 @@ class MeshFormatHandler:
         # Create a list from the supported file formats string.
         if not global_stack:
             Logger.log("e", "Missing global stack!")
-            return
+            return {}
 
         machine_file_formats = global_stack.getMetaDataEntry("file_formats").split(";")
         machine_file_formats = [file_type.strip() for file_type in machine_file_formats]