按列排序
res = df[df['_key'] == _id].reset_index(drop=True).sort_values(by=colname, ascending=False, axis=0)
将date变为index，从DataDrame中抽出时间序列
df = df[['col_a', 'col_b']].rename(columns={'col_a': 'date', 'col_b': 'value'}).set_index('date')
df.index = pd.to_datetime(df.index, format='%Y-%m')
ts = df['value']
去掉某列的空值
df = df[df['colname'].notnull()]
列类型强制转换，表的切片
df_new = df[['col_a', 'col_b']]
df['col_a'] = df['col_a'].astype(np.int64)
