门 | GATE-CS-2016（套装2）|问题 20

这道题目要求我们实现一个门的类，门有两种状态：开和关。门可以被打开和关闭，但是如果门已经处于想要走的状态，那么什么都不会发生。门还有一个状态，用于判断是否被锁住，因此门可以处于四种不同的状态之一。

实现门的类

我们可以实现一个门的类，该类有一个状态属性，表示门的状态以及一些方法。

class Door:
    """Represents a door."""

    def __init__(self):
        """Initializes the door as closed and unlocked."""
        self._is_closed = True
        self._is_locked = False

    def open(self):
        """Opens the door."""
        if not self._is_locked and self._is_closed:
            self._is_closed = False
            print("Door is now open.")
        elif self._is_locked:
            print("Cannot open door. It is locked.")
        else:
            print("Door is already open.")

    def close(self):
        """Closes the door."""
        if self._is_closed:
            print("Door is already closed.")
        else:
            self._is_closed = True
            print("Door is now closed.")

    def lock(self):
        """Locks the door."""
        if self._is_locked:
            print("Door is already locked.")
        else:
            self._is_locked = True
            print("Door is now locked.")

    def unlock(self):
        """Unlocks the door."""
        if not self._is_locked:
            print("Door is already unlocked.")
        else:
            self._is_locked = False
            print("Door is now unlocked.")

使用门的类

我们可以使用门的类来创建门实例，并对门进行打开、关闭、锁定和解锁操作。

# Create a door instance
door = Door()

# Open the door
door.open()     # Output: Door is now open.

# Try to open the door when it is already open
door.open()     # Output: Door is already open.

# Close the door
door.close()    # Output: Door is now closed.

# Try to close the door when it is already closed
door.close()    # Output: Door is already closed.

# Lock the door
door.lock()     # Output: Door is now locked.

# Try to open the door when it is locked
door.open()     # Output: Cannot open door. It is locked.

# Unlock the door
door.unlock()   # Output: Door is now unlocked.

# Open the door after unlocking it
door.open()     # Output: Door is now open.

如上所示，在门的实例上直接使用方法，可以执行开门、关门、锁门、打开门等方法，然后我们可以按照门的状态进行操作。