df.loc[df[1:][df.index.month[:-1] != df.index.month[1:]].index]
df.loc[df[:-1][df.index.month[:-1] != df.index.month[1:]].index]
fr1 = df.groupby(df.index.year * 100 + df.index.month).apply(lambda x: x[(x
    .index.week == 1) * (x.index.weekday == 4)])
How to select observations of df using datetime index atributes in Pandas?