Stylesheet: Don't compute stylesheets when importing the module

spyder/utils/stylesheet.py

@@ -31,13 +31,21 @@ class SpyderStyleSheet:
 
     def __init__(self):
         self._stylesheet = qstylizer.style.StyleSheet()
-        self.set_stylesheet()
+        self._stylesheet_as_string = None
 
     def get_stylesheet(self):
         return self._stylesheet
 
     def to_string(self):
-        return self._stylesheet.toString()
+        "Save stylesheet as a string for quick access."
+        if self._stylesheet_as_string is None:
+            # Leave this line here so that stylesheets are computed when
+            # used and not when importing this module.
+            self.set_stylesheet()
+
+            # Cache stylesheet string
+            self._stylesheet_as_string = self._stylesheet.toString()
+        return self._stylesheet_as_string
 
     def get_copy(self):
         """
@@ -50,10 +58,14 @@ def get_copy(self):
     def set_stylesheet(self):
         raise NotImplementedError(
             "Subclasses need to implement this method to set the _stylesheet "
-            "attribute as a Qstylizer StyleSheet object"
+            "attribute as a Qstylizer StyleSheet object."
         )
 
     def __str__(self):
+        """
+        Get a string representation of the stylesheet object this class
+        holds.
+        """
         return self.to_string()
 
 
@@ -66,16 +78,6 @@ class AppStylesheet(SpyderStyleSheet):
     application.
     """
 
-    def __init__(self):
-        super().__init__()
-        self._stylesheet_as_string = None
-
-    def to_string(self):
-        "Save stylesheet as a string for quick access."
-        if self._stylesheet_as_string is None:
-            self._stylesheet_as_string = self._stylesheet.toString()
-        return self._stylesheet_as_string
-
     def set_stylesheet(self):
         """
         This takes the stylesheet from QDarkstyle and applies our
@@ -335,6 +337,7 @@ def set_stylesheet(self):
         )
 
     def to_string(self):
+        super().to_string()
         css_string = self._stylesheet.toString()
 
         # TODO: We need to fix this in qstylizer