strptime()报错

dt = datetime.strptime(x, '%Y-%m-%d %H:%M:%S.%f')

TypeError: strptime() argument 1 must be str, not int

import pandas as pd

from datetime import datetime, timedelta

data =pd.read_csv('C:/Users/admin/Desktop/test.csv')  

def time_format(x):

    dt = datetime.strptime(x, '%Y-%m-%d %H:%M:%S.%f')    

    mod = (dt.minute // 15)

    if mod == 0:

        if dt.minute == 0:

            return datetime(dt.year, dt.month, dt.day, dt.hour, dt.minute,

dt.second, dt.microsecond)

        else:

            minute = mod * 15

            return datetime(dt.year, dt.month, dt.day, dt.hour, minute,

dt.second, dt.microsecond) + timedelta(minutes=15)

    else:

        minute = mod * 15

        return datetime(dt.year, dt.month, dt.day, dt.hour, minute,

dt.second, dt.microsecond) + timedelta(minutes=15)



df = data.fillna(0)

df['DateTimeKey'] = df['DateTimeKey'].apply(time_format)

print(df.groupby('DateTimeKey', as_index=False).sum())