remove CellInvalidWallError, more refactoring

- Move the custom exceptions to errors.py
- Created enums to label the cell walls. Replaces the constants defined
  in the Cell class.

cell.py

@@ -1,5 +1,18 @@
 from typing import Dict
+from enum import Enum
 from graphics import Window, Point, Line
+import errors
+
+
+class CellWallLabel(Enum):
+    """
+    CellWallLabel is used to label a CellWall
+    """
+
+    TOP = 0
+    BOTTOM = 1
+    LEFT = 2
+    RIGHT = 3
 
 
 class CellWall:
@@ -26,11 +39,6 @@ class Cell:
     A Cell represents a grid on the maze.
     """
 
-    TOP_WALL = 0
-    BOTTOM_WALL = 1
-    LEFT_WALL = 2
-    RIGHT_WALL = 3
-
     def __init__(
             self,
             x1: int, y1: int,
@@ -39,13 +47,13 @@ class Cell:
     ) -> None:
         # Validation
         if (x2 < x1) or (y2 < y1):
-            raise CellInvalidError(x1, y1, x2, y2)
+            raise errors.CellInvalidError(x1, y1, x2, y2)
 
         if (x2 - x1) < 2:
-            raise CellTooSmallError("horizontal", x2-x1)
+            raise errors.CellTooSmallError("horizontal", x2-x1)
 
         if (y2 - y1) < 2:
-            raise CellTooSmallError("vertical", y2-y1)
+            raise errors.CellTooSmallError("vertical", y2-y1)
 
         # Define the cell walls
         top_wall = Line(Point(x1, y1), Point(x2, y1))
@@ -53,11 +61,11 @@ class Cell:
         left_wall = Line(Point(x1, y1), Point(x1, y2))
         right_wall = Line(Point(x2, y1), Point(x2, y2))
 
-        self._walls: Dict[int, CellWall] = {
-            Cell.TOP_WALL: CellWall(top_wall, window),
-            Cell.BOTTOM_WALL: CellWall(bottom_wall, window),
-            Cell.LEFT_WALL: CellWall(left_wall, window),
-            Cell.RIGHT_WALL: CellWall(right_wall, window),
+        self._walls: Dict[CellWallLabel, CellWall] = {
+            CellWallLabel.TOP: CellWall(top_wall, window),
+            CellWallLabel.BOTTOM: CellWall(bottom_wall, window),
+            CellWallLabel.LEFT: CellWall(left_wall, window),
+            CellWallLabel.RIGHT: CellWall(right_wall, window),
         }
 
         # Calculate the cell's central point
@@ -80,10 +88,10 @@ class Cell:
         """
         configure_walls configures the existence of the Cell's walls.
         """
-        self._walls[Cell.TOP_WALL].exists = top
-        self._walls[Cell.BOTTOM_WALL].exists = bottom
-        self._walls[Cell.LEFT_WALL].exists = left
-        self._walls[Cell.RIGHT_WALL].exists = right
+        self._walls[CellWallLabel.TOP].exists = top
+        self._walls[CellWallLabel.BOTTOM].exists = bottom
+        self._walls[CellWallLabel.LEFT].exists = left
+        self._walls[CellWallLabel.RIGHT].exists = right
 
     def centre(self) -> Point:
         """
@@ -91,9 +99,10 @@ class Cell:
         """
         return self._centre
 
-    def wall_exists(self, wall: int) -> bool:
-        if wall not in self._walls:
-            raise CellInvalidWallError(wall)
+    def wall_exists(self, wall: CellWallLabel) -> bool:
+        """
+        returns True if a given cell wall exists, or false otherwise.
+        """
         return self._walls[wall].exists
 
     # def break_walls_r(self, i: int, j: int) -> None:
@@ -110,8 +119,8 @@ class Cell:
         if not self._window:
             return
 
-        for _, wall in self._walls.items():
-            wall.draw()
+        for label in CellWallLabel:
+            self._walls[label].draw()
 
     def draw_move(self, to_cell: 'Cell', undo: bool = False) -> None:
         """
@@ -126,52 +135,3 @@ class Cell:
             fill_colour = "grey"
         line = Line(self.centre(), to_cell.centre())
         self._window.draw_line(line, fill_colour)
-
-
-class CellInvalidWallError(Exception):
-    """
-    CellInvalidWallError is raised when the program tries to specify a Cell's
-    Wall that does not exist.
-    """
-
-    def __init__(self, wall: int, *args):
-        super().__init__(args)
-        self.wall = wall
-
-    def __str__(self):
-        return f"Invalid Cell Wall (wall int: {self.wall}) specified."
-
-
-class CellInvalidError(Exception):
-    """
-    CellInvalidError is raised when the program tries to create a Cell whose
-    values are invalid. The values are invalid when x2 is smaller than x1
-    and/or y2 is smaller than y1. When creating a Cell the x and y values
-    should always represent the top left and the bottom right corners of
-    the cell (i.e. x1 < x2 and y1 < y2).
-    """
-
-    def __init__(self, x1: int, y1: int, x2: int, y2: int, *args):
-        super().__init__(args)
-        self.x1 = x1
-        self.x2 = x2
-        self.y1 = y1
-        self.y2 = y2
-
-    def __str__(self):
-        return f"Invalid Cell values received. Please ensure that both: x1 ({self.x1}) < x2 ({self.x2}), and y1 ({self.y1}) < y2 ({self.y2})"
-
-
-class CellTooSmallError(Exception):
-    """
-    CellTooSmallError is raised when the program tries to create a Cell
-    which is too small to correctly draw it's central point.
-    """
-
-    def __init__(self, size_type: str, size: int, *args):
-        super().__init__(args)
-        self.size_type = size_type
-        self.size = size
-
-    def __str__(self):
-        return f"The {self.size_type} size of the cell ({self.size}) is too small."

errors.py

@@ -0,0 +1,33 @@
+class CellInvalidError(Exception):
+    """
+    CellInvalidError is raised when the program tries to create a Cell whose
+    values are invalid. The values are invalid when x2 is smaller than x1
+    and/or y2 is smaller than y1. When creating a Cell the x and y values
+    should always represent the top left and the bottom right corners of
+    the cell (i.e. x1 < x2 and y1 < y2).
+    """
+
+    def __init__(self, x1: int, y1: int, x2: int, y2: int, *args):
+        super().__init__(args)
+        self.x1 = x1
+        self.x2 = x2
+        self.y1 = y1
+        self.y2 = y2
+
+    def __str__(self):
+        return f"Invalid Cell values received. Please ensure that both: x1 ({self.x1}) < x2 ({self.x2}), and y1 ({self.y1}) < y2 ({self.y2})"
+
+
+class CellTooSmallError(Exception):
+    """
+    CellTooSmallError is raised when the program tries to create a Cell
+    which is too small to correctly draw it's central point.
+    """
+
+    def __init__(self, size_type: str, size: int, *args):
+        super().__init__(args)
+        self.size_type = size_type
+        self.size = size
+
+    def __str__(self):
+        return f"The {self.size_type} size of the cell ({self.size}) is too small."

maze.py

@@ -39,9 +39,12 @@ class Maze:
         # Create the Maze's cells
         self._cells: List[List[Cell]] = [None for i in range(self._num_cell_rows)]
         self._create_cells()
-        self._break_entrance_and_exit()
+        self._open_entrance_and_exit()
 
-    def _create_cells(self):
+    def _create_cells(self) -> None:
+        """
+        creates all the cells and draws them.
+        """
         cursor_x = self._x_position
         cursor_y = self._y_position
 
@@ -66,20 +69,32 @@ class Maze:
         if self._window:
             self._draw_cells()
 
-    def _break_entrance_and_exit(self):
-        # break entrance and draw
+    def _open_entrance_and_exit(self) -> None:
+        """
+        opens the maze's entrance and exit cells by breaking their respective
+        walls. The entrance is located at the top left and the exit is located
+        at the bottom right of the maze.
+        """
         self._cells[0][0].configure_walls(top=False)
         self._cells[0][0].draw()
-        # break exit and draw
+
         self._cells[self._num_cell_rows - 1][self._num_cells_per_row - 1].configure_walls(bottom=False)
         self._cells[self._num_cell_rows - 1][self._num_cells_per_row - 1].draw()
 
-    def _draw_cells(self):
+    def _draw_cells(self) -> None:
+        """
+        draws all the cells on the maze with a short pause between each cell
+        for animation purposes.
+        """
         for i in range(self._num_cell_rows):
             for j in range(self._num_cells_per_row):
                 self._cells[i][j].draw()
                 self._animate()
 
-    def _animate(self):
+    def _animate(self) -> None:
+        """
+        redraws the application and pauses for a short period of time to
+        provide an animation effect.
+        """
         self._window.redraw()
         sleep(0.05)

tests.py

@@ -1,7 +1,7 @@
 import unittest
-import cell
-from cell import Cell
+from cell import Cell, CellWallLabel
 from maze import Maze
+import errors
 
 
 class Tests(unittest.TestCase):
@@ -57,10 +57,10 @@ class Tests(unittest.TestCase):
             2,
             2,
         )
-        self.assertFalse(maze._cells[0][0].wall_exists(Cell.TOP_WALL))
+        self.assertFalse(maze._cells[0][0].wall_exists(CellWallLabel.TOP))
         self.assertFalse(
             maze._cells[number_of_cell_rows - 1]
-            [number_of_cells_per_row - 1].wall_exists(Cell.BOTTOM_WALL)
+            [number_of_cells_per_row - 1].wall_exists(CellWallLabel.BOTTOM)
         )
 
     def test_invalid_cell_exception(self):
@@ -74,7 +74,7 @@ class Tests(unittest.TestCase):
         ]
 
         for case in cases:
-            with self.assertRaises(cell.CellInvalidError):
+            with self.assertRaises(errors.CellInvalidError):
                 _ = Cell(
                     x1=case["x1"],
                     y1=case["y1"],
@@ -93,7 +93,7 @@ class Tests(unittest.TestCase):
         ]
 
         for case in cases:
-            with self.assertRaises(cell.CellTooSmallError):
+            with self.assertRaises(errors.CellTooSmallError):
                 _ = Cell(
                     x1=case["x1"],
                     y1=case["y1"],