# Complication # We have a new product feature: reserving money through a mobile app. # For this, we need to add a new method reserve(amount) to the ATM class. Also, we should consider HardwareError in SDK methods.

To add new functionality for reserving money in the ATM class, you need to:

1. Add a method reserve(amount) that interacts with the SDK to lock the amount.
2. Handle the possible HardwareError exception in SDK methods to respond correctly to hardware errors.

Example in Python:

class HardwareError(Exception):
    pass

class ATM:
    def __init__(self, sdk):
        self.sdk = sdk

    def reserve(self, amount):
        try:
            self.sdk.block_amount(amount)
        except HardwareError as e:
            # Log the error, notify the user, or take recovery actions
            print(f"Hardware error during reservation: {e}")
            raise

    def withdraw(self, amount):
        try:
            self.sdk.dispense_cash(amount)
        except HardwareError as e:
            print(f"Hardware error during cash dispensing: {e}")
            raise

Thus, the new reserve method adds reservation functionality, and handling HardwareError allows reliable operation with hardware failures.