gistfile1.txt

import datetime
df = pd.DataFrame({'Month': [datetime.date(2008, i, 1).strftime('%B') for i in range(1,13)] * 3, 
                   'visited': [False]*36},
                 index= ['Alice']*12 + ['Bob']*12 + ['Bridgett']*12)

df = df.reset_index()
df [(df['index'] == 'Alice') & 
                  ((df['Month'] == 'February') | (df['Month'] == 'March') | (df['Month'] == 'April'))]

def make_regular(r, name):
    r['visited'] = (r['visited'] or (r['index'] == name) and 
                  ((r['Month'] == 'February') or (r['Month'] == 'March') or (r['Month'] == 'April')))
    return r

df = df.apply(make_regular, axis=1, args=('Alice',))
df = df.apply(make_regular, axis=1, args=('Bob',))
regular = (df['visited'] == True) & (df['visited'].shift(-1) == True) & (df['visited'].shift(-2) == True)
df[regular]['index'].values .tolist()