Retranslate the complete English edition from Simplified Chinese (#2010)

* Retranslate the complete English edition from Simplified Chinese

* Polish three English explanations after reader-focused review

en/codes/python/chapter_tree/binary_tree_bfs.py

@@ -14,29 +14,29 @@ from collections import deque
 
 def level_order(root: TreeNode | None) -> list[int]:
     """Level-order traversal"""
-    # Initialize queue, add root node
+    # Initialize a queue and enqueue the root
     queue: deque[TreeNode] = deque()
     queue.append(root)
-    # Initialize a list to save the traversal sequence
+    # Initialize a list to store the traversal sequence
     res = []
     while queue:
-        node: TreeNode = queue.popleft()  # Dequeue
-        res.append(node.val)  # Save node value
+        node: TreeNode = queue.popleft()  # Dequeue from the queue
+        res.append(node.val)  # Store the node value
         if node.left is not None:
-            queue.append(node.left)  # Left child node enqueue
+            queue.append(node.left)  # Enqueue the left child
         if node.right is not None:
-            queue.append(node.right)  # Right child node enqueue
+            queue.append(node.right)  # Enqueue the right child
     return res
 
 
-"""Driver Code"""
+"""Driver code"""
 if __name__ == "__main__":
-    # Initialize binary tree
-    # Here we use a function to generate a binary tree directly from an array
+    # Initialize the binary tree
+    # Use a helper function that builds a binary tree directly from an array
     root: TreeNode = list_to_tree(arr=[1, 2, 3, 4, 5, 6, 7])
-    print("\nInitialize binary tree\n")
+    print("\nInitialize the binary tree\n")
     print_tree(root)
 
     # Level-order traversal
     res: list[int] = level_order(root)
-    print("\nLevel-order traversal node print sequence = ", res)
+    print("\nNode sequence from level-order traversal = ", res)