Create a class called VendingMachine that represents a vending machine for some product. A VendingMachine object returns strings describing its interactions. Fill in the VendingMachine class, adding attributes and methods as appropriate, such that its behavior matches the following doctests:

Sure, here's an implementation of the `VendingMachine` class that satisfies the given requirements:

class VendingMachine:
    def __init__(self, product_name, price):
        self.product_name = product_name
        self.price = price
        self.balance = 0
        self.stock = 0
    
    def restock(self, amount):
        self.stock += amount
        return f"Current {self.product_name} stock: {self.stock}"
    
    def deposit(self, amount):
        if self.stock == 0:
            return f"Machine is out of stock. Here is your ${amount} back."
        self.balance += amount
        return f"Current balance: ${self.balance}"
    
    def vend(self):
        if self.stock == 0:
            return "Machine is out of stock."
        if self.balance < self.price:
            return f"You must deposit ${self.price - self.balance} more."
        self.stock -= 1
        self.balance -= self.price
        if self.balance == 0:
            return f"Here is your {self.product_name}."
        return f"Here is your {self.product_name} and ${self.balance} change."

Here are the doctests to verify the behavior:

# Create a vending machine that sells chips for $1.50
>>> machine = VendingMachine('chips', 1.50)

# Restock the machine with 10 chips
>>> machine.restock(10)
'Current chips stock: 10'

# Deposit $1.00 into the machine
>>> machine.deposit(1.00)
'Current balance: $1.00'

# Vend a chip with only $1.00 deposited
>>> machine.vend()
'You must deposit $0.50 more.'

# Deposit $1.50 into the machine
>>> machine.deposit(1.50)
'Current balance: $2.50'

# Vend a chip with $2.50 deposited
>>> machine.vend()
'Here is your chips and $1.00 change.'

# Vend a chip when the machine is out of stock
>>> machine.vend()
'Machine is out of stock.'

# Deposit $1.00 into an empty machine
>>> machine.deposit(1.00)
'Machine is out of stock. Here is your $1.00 back.'