input: Write a python function to compare prices from two stores and return the price difference.
  assert compare_prices('productA', 'storeX', 'productB', 'storeY') == {'store1': 'storeX', 'store2': 'storeY', 'product1': 'productA', 'product2': 'productB', 'price1': 100.0, 'price2': 120.0, 'difference': 20.0}
  assert compare_prices('productC', 'storeZ', 'productD', 'storeW') == {'store1': 'storeZ', 'store2': 'storeW', 'product1': 'productC', 'product2': 'productD', 'price1': 50.0, 'price2': 45.0, 'difference': -5.0}
output: def compare_prices(product1, store1, product2, store2):
      # Here we simulate the prices for the sake of the example.
      # In a real-world scenario, you would retrieve this data from a database or an API.
      prices = {
          'storeX': {'productA': 100.0},
          'storeY': {'productB': 120.0},
          'storeZ': {'productC': 50.0},
          'storeW': {'productD': 45.0},
      }
      
      price1 = prices.get(store1, {}).get(product1, 0.0)
      price2 = prices.get(store2, {}).get(product2, 0.0)
      
      difference = price2 - price1
      
      return {
          'store1': store1,
          'store2': store2,
          'product1': product1,
          'product2': product2,
          'price1': price1,
          'price2': price2,
          'difference': difference
      }