AttributeError: 'unicode' 对象没有属性 'strftime'

如何解决AttributeError: 'unicode' 对象没有属性 'strftime'

import arcpy,os

from arcpy.sa import *


arcpy.env.overwriteOutput = True

fc = r'E:\dada proj\DRAW OBJECTS\VIPPoints.mdb\Allfeat'
# Point feature class,needs to be in a file geodatabase (for the where clause to work)
output_folder = r'C:\GIS\data\testdata'  # Where the rasters will be saved

date_field = 'date_'  # field holding the dates (date type,not string)
value_fields = ['CO','O3','NO2']  # field with the values to interpolate

all_dates = list({i[0] for i in arcpy.da.SearchCursor(fc,date_field)})  # List all unique dates



for date in all_dates:
    # Create a feature layer of each unique date
    where = "{0}=date '{1}'".format(arcpy.AddFieldDelimiters(datasource=fc,field=date_field),date.strftime('%Y-%m-%d'))
    arcpy.MakeFeatureLayer_management(in_features=fc,out_layer='lyr',where_clause=where)

    # For each field interpolate. This is untested since I dont have spatial analyst
    for fieldname in value_fields:
        outIDW = Idw(in_point_features='lyr',z_field=fieldname,cell_size=10)  #,{power},{search_radius},{in_barrier_polyline_features})
        outIDW.save(os.path.join(output_folder,'{0}_{1}.tif'.format(fieldname,date.strftime('%Y%m%d'))))

运行时出错

AttributeError: 'unicode' object has no attribute 'strftime'

我的日期在表格和格式中：yyyy/mm/dd 感谢任何解决错误的建议