python - Looping through pandas dataframe for speed -

i'm trying understand fastest way loop through in pandas. read in many places itertuples better regularly looping through data, , best apply. if case why regular loops come out fastest? maybe i'm not understanding results, 10 loops, best of 3 mean?

%%timeit xlist= [] row in tomood.itertuples():     xlist.append(row[1] + 1) 1 loop, best of 3: 266 ms per loop in [54]:   %%timeit zlist = [] row in tomood['user_id']:     zlist.append(row + 1) 10 loops, best of 3: 83 ms per loop in [56]:  %%timeit tlist = tomood['user_id'].apply(lambda x: x+1) 10 loops, best of 3: 138 ms per loop