Pandas .loc with a list returns a series, not a scalar

Pass a list to .loc on a Python Pandas series, and get a series back:

s = pd.Series([10, 20, 30], index=list('abc'))

s.loc[['a']]       # series, a:10
s.loc[['a', 'b']]  # series, a:10, b:20
s.loc[['a', 'a']]  # series, a:10 twice!
s.loc[['b', 'a']]  # series, b:20, a:10