python dataframe计算日期对应的周数或者星期几

import pandas as pd
import datetime
a=['20211001','20211002','20211003','20211003','20211004']
df=pd.Dataframe(a,columns=['t'])
df['t2'] = pd.to_datetime(df['t'])
df['day_of_week'] =  pd.to_datetime(df['t']).dt.week
df['week'] = df['t2'].dt.weekday
df['week_name'] = df['t2'].dt.weekday_name
df