Running balance

entries is a list of (description, amount) tuples; positive amounts are money in, negative money out. Write ledger(entries) that returns a list of strings <description>: <balance> showing the balance after each entry, and stops early with the string "OVERDRAWN" as the last line if the balance ever goes below zero.

ledger([("sale", 50), ("rent", -30), ("sale", 10)])  ->  ["sale: 50", "rent: 20", "sale: 30"]
ledger([("sale", 10), ("rent", -30), ("sale", 100)])  ->  ["sale: 10", "rent: -20", "OVERDRAWN"]

def ledger(entries):
    ...