写一个共享单车的代码

这里是一个简单的共享单车的 Python 代码，实现了用户注册、借车、还车、充值等功能：

class User:
    def __init__(self, name, balance=0):
        self.name = name
        self.balance = balance
        self.borrowed_bike = None

    def borrow_bike(self, bike):
        if self.borrowed_bike is not None:
            print("You have already borrowed a bike!")
            return False
        if bike.borrow_by is not None:
            print("Sorry, this bike has been borrowed by someone else!")
            return False
        self.borrowed_bike = bike
        bike.borrow_by = self
        print("You have successfully borrowed a bike!")
        return True

    def return_bike(self):
        if self.borrowed_bike is None:
            print("You haven't borrowed any bike yet!")
            return False
        self.borrowed_bike.borrow_by = None
        self.borrowed_bike = None
        print("You have successfully returned the bike!")
        return True

    def recharge(self, amount):
        self.balance += amount
        print("You have successfully recharged {} yuan!".format(amount))


class Bike:
    def __init__(self, bike_id):
        self.bike_id = bike_id
        self.borrow_by = None


class BikeSharingSystem:
    def __init__(self):
        self.users = {}
        self.bikes = {}
        self.bike_id_counter = 0

    def add_user(self, name, balance=0):
        if name in self.users:
            print("User {} already exists!".format(name))
            return False
        self.users[name] = User(name, balance)
        print("User {} has been added to the system!".format(name))
        return True

    def add_bike(self):
        bike_id = str(self.bike_id_counter)
        self.bike_id_counter += 1
        self.bikes[bike_id] = Bike(bike_id)
        print("Bike {} has been added to the system!".format(bike_id))
        return True

    def borrow_bike(self, user_name, bike_id):
        if user_name not in self.users:
            print("User {} does not exist!".format(user_name))
            return False
        if bike_id not in self.bikes:
            print("Bike {} does not exist!".format(bike_id))
            return False
        return self.users[user_name].borrow_bike(self.bikes[bike_id])

    def return_bike(self, user_name):
        if user_name not in self.users:
            print("User {} does not exist!".format(user_name))
            return False
        return self.users[user_name].return_bike()

    def recharge(self, user_name, amount):
        if user_name not in self.users:
            print("User {} does not exist!".format(user_name))
            return False
        self.users[user_name].recharge(amount)
        return True

使用方法：

system = BikeSharingSystem()
system.add_user("Alice", 100)
system.add_user("Bob", 50)
system.add_bike()

system.borrow_bike("Alice", "0")
system.borrow_bike("Bob", "0")

system.return_bike("Alice")
system.borrow_bike("Bob", "0")

system.recharge("Alice", 50)