Add docstrings. Also add safe_cast function. Finally

fix some minor issues.

fixed_aspect_ratio_label.py

@@ -3,21 +3,29 @@ from PyQt5.QtCore import Qt
 
 
 class FixedAspectRatioLabel(QLabel):
+    """Subclass QLabel. A resizable label class."""
+
     def __init__(self, parent = None):
+        """Initialize the instance. Set the pixmap to None."""
         super().__init__(parent)
         self.pixmap = None
 
     def set_default_stylesheet(self):
+        """Set the initial stylesheet of the label."""
         self.setStyleSheet("""border-width: 1px;
         border-style: solid;
         border-color: black;"""
         )
 
     def make_transparent(self):
+        """Make the label transparent.
+
+        Remove text and border."""
         self.setText('')
         self.setStyleSheet("border-width: 0px;")
 
     def apply_pixmap(self):
+        """Apply a scaled pixmap without modifying the dimension of the original one."""
         if self.pixmap:
             self.setPixmap(
                 self.pixmap.scaled(
@@ -26,5 +34,6 @@ class FixedAspectRatioLabel(QLabel):
             )
 
     def rescale(self, size):
+        """Rescale the widget and the displayed pixmap to the given size."""
         self.resize(size)
         self.apply_pixmap()