print(gifts.head(2))

   donor_id
0     65537
1     65538

# Target period
start_target = datetime(year = 2017, month = 1, day = 1)
end_target = datetime(year = 2018, month = 1, day = 1)

# Select target period donations
gifts_target = gifts[(gifts["date"]>=start_target) & (gifts["date"]<end_target)]

# Group and sum donations by donor
gifts_target_byid = gifts_target.groupby("id")["amount"].sum().reset_index()

# Derive targets and add to basetable
targets = list(gifts_target_byid["id"][gifts_target_byid["amount"]>500])

basetable["target"] = pd.Series([1 if donor_id in targets else 0 for donor_id in basetable["donor_id"]])