Typing fixes

Since I was stupid enough to touch it, I was also forced to boyscout the code.

plugins/PostProcessingPlugin/Script.py

@@ -1,6 +1,8 @@
 # Copyright (c) 2015 Jaime van Kessel
 # Copyright (c) 2018 Ultimaker B.V.
 # The PostProcessingPlugin is released under the terms of the AGPLv3 or higher.
+from typing import Optional, Any, Dict, TYPE_CHECKING, List
+
 from UM.Signal import Signal, signalemitter
 from UM.i18n import i18nCatalog
 
@@ -17,16 +19,20 @@ import json
 import collections
 i18n_catalog = i18nCatalog("cura")
 
+if TYPE_CHECKING:
+    from UM.Settings.Interfaces import DefinitionContainerInterface
+
 
 ## Base class for scripts. All scripts should inherit the script class.
 @signalemitter
 class Script:
-    def __init__(self):
+    def __init__(self) -> None:
         super().__init__()
-        self._settings = None
-        self._stack = None
+        self._stack = None  # type: Optional[ContainerStack]
+        self._definition = None  # type: Optional[DefinitionContainerInterface]
+        self._instance = None  # type: Optional[InstanceContainer]
 
-    def initialize(self):
+    def initialize(self) -> None:
         setting_data = self.getSettingData()
         self._stack = ContainerStack(stack_id=str(id(self)))
         self._stack.setDirty(False)  # This stack does not need to be saved.
@@ -45,6 +51,8 @@ class Script:
                 except ContainerFormatError:
                     self._definition = None
                     return
+        if self._definition is None:
+            return
         self._stack.addContainer(self._definition)
         self._instance = InstanceContainer(container_id="ScriptInstanceContainer")
         self._instance.setDefinition(self._definition.getId())
@@ -58,16 +66,17 @@ class Script:
     settingsLoaded = Signal()
     valueChanged = Signal()  # Signal emitted whenever a value of a setting is changed
 
-    def _onPropertyChanged(self, key, property_name):
+    def _onPropertyChanged(self, key: str, property_name: str) -> None:
         if property_name == "value":
             self.valueChanged.emit()
 
             # Property changed: trigger reslice
             # To do this we use the global container stack propertyChanged.
-            # Reslicing is necessary for setting changes in this plugin, because the changes
+            # Re-slicing is necessary for setting changes in this plugin, because the changes
             # are applied only once per "fresh" gcode
             global_container_stack = Application.getInstance().getGlobalContainerStack()
-            global_container_stack.propertyChanged.emit(key, property_name)
+            if global_container_stack is not None:
+                global_container_stack.propertyChanged.emit(key, property_name)
 
     ##  Needs to return a dict that can be used to construct a settingcategory file.
     #   See the example script for an example.
@@ -75,30 +84,35 @@ class Script:
     #   Scripts can either override getSettingData directly, or use getSettingDataString
     #   to return a string that will be parsed as json. The latter has the benefit over
     #   returning a dict in that the order of settings is maintained.
-    def getSettingData(self):
-        setting_data = self.getSettingDataString()
-        if type(setting_data) == str:
-            setting_data = json.loads(setting_data, object_pairs_hook = collections.OrderedDict)
+    def getSettingData(self) -> Dict[str, Any]:
+        setting_data_as_string = self.getSettingDataString()
+        setting_data = json.loads(setting_data_as_string, object_pairs_hook = collections.OrderedDict)
         return setting_data
 
-    def getSettingDataString(self):
+    def getSettingDataString(self) -> str:
         raise NotImplementedError()
 
-    def getDefinitionId(self):
+    def getDefinitionId(self) -> Optional[str]:
         if self._stack:
-            return self._stack.getBottom().getId()
+            bottom = self._stack.getBottom()
+            if bottom is not None:
+                return bottom.getId()
+        return None
 
-    def getStackId(self):
+    def getStackId(self) -> Optional[str]:
         if self._stack:
             return self._stack.getId()
+        return None
 
     ##  Convenience function that retrieves value of a setting from the stack.
-    def getSettingValueByKey(self, key):
-        return self._stack.getProperty(key, "value")
+    def getSettingValueByKey(self, key: str) -> Any:
+        if self._stack is not None:
+            return self._stack.getProperty(key, "value")
+        return None
 
     ##  Convenience function that finds the value in a line of g-code.
     #   When requesting key = x from line "G1 X100" the value 100 is returned.
-    def getValue(self, line, key, default = None):
+    def getValue(self, line: str, key: str, default = None) -> Any:
         if not key in line or (';' in line and line.find(key) > line.find(';')):
             return default
         sub_part = line[line.find(key) + 1:]
@@ -126,7 +140,7 @@ class Script:
     #   \param line The original g-code line that must be modified. If not
     #   provided, an entirely new g-code line will be produced.
     #   \return A line of g-code with the desired parameters filled in.
-    def putValue(self, line = "", **kwargs):
+    def putValue(self, line: str = "", **kwargs) -> str:
         #Strip the comment.
         comment = ""
         if ";" in line:
@@ -167,5 +181,5 @@ class Script:
 
     ##  This is called when the script is executed. 
     #   It gets a list of g-code strings and needs to return a (modified) list.
-    def execute(self, data):
+    def execute(self, data: List[str]) -> List[str]:
         raise NotImplementedError()