How to Fix Saga Pattern Errors

def place_order(order):
    payment.process(order)
    inventory.reserve(order)
    shipping.schedule(order)
    # If shipping fails, payment already processed and inventory reserved!

class Saga:
    def __init__(self): self.steps=[]; self.compensations=[]
    def add_step(self,action,compensate):
        self.steps.append(action); self.compensations.append(compensate)
    def execute(self,ctx):
        completed=[]
        try:
            for i,step in enumerate(self.steps):
                step(ctx); completed.append(i)
        except Exception as e:
            print(f'Failed at step {i}: {e}. Compensating...')
            for idx in reversed(completed):
                try: self.compensations[idx](ctx)
                except: pass
            raise
# Usage:
saga=Saga()
saga.add_step(lambda ctx: print('Payment OK'), lambda ctx: print('Payment refund'))
saga.add_step(lambda ctx: print('Inventory reserved'), lambda ctx: print('Inventory released'))
saga.add_step(lambda ctx: exec('raise Exception("Ship fail")'), lambda ctx: print('Shipping cancelled'))
try: saga.execute({})
except: print('Saga rolled back')