add missing import

app.py

@@ -4,6 +4,7 @@ from ocean_lib.models.btoken import BToken #BToken is ERC20
 from ocean_lib.ocean.ocean import Ocean
 from ocean_lib.web3_internal.wallet import Wallet
 from ocean_lib.web3_internal.currency import from_wei # wei is the smallest denomination of ether e.g. like cents
+from ocean_lib.web3_internal.currency import pretty_ether_and_wei
 
 config = Config('config.ini')
 ocean = Ocean(config)