我无法在spark sql中传递日期字符串
当我运行这个

spark.sql(""" SELECT cast ('2021-04-12' as date) """)
> DataFrame[CAST(2021-04-12 AS DATE): date]

但是，当我想把日期字符串作为变量传递时，我得到了一个错误

date_str = '2021-04-12'
 spark.sql(""" SELECT cast ({} as date) """.format(date_str))

 > AnalysisException: cannot resolve 'CAST(((2021 - 4) - 12) AS DATE)' 
 > due to data type mismatch: cannot cast int to date; line 1 pos 7;

我不知道如何传递那个变量。