drop table t1;

create table t1(p1 varchar2(10),
rdate varchar2(6))
 partition by list (rdate)
(  partition PRT_201912 values ('201912'),
   partition PRT_202001 values ('202001'),
   partition PRT_202002 values ('202002'),
    partition PRT_FAKE values (DEFAULT));

insert into t1 values('1','201912');
insert into t1 values('2','201912');
insert into t1 values('3','202001');
insert into t1 values('4','201908');


SQL> select count(*)  from t1 partition for (201912);

  COUNT(*)
----------
         2



set serveroutput on
declare 
cnt number;
begin
 for rd in (select distinct  rdate from t1) loop
  dbms_output.put_line(rd.rdate||'**** ');
   select count(*) into cnt from t1 partition for (to_number(rd.rdate));
   dbms_output.put_line(rd.rdate||'= '|| cnt);
 end loop; 
dbms_output.put_line('end ');
end;
/

201912****
declare
*
ERROR at line 1:
ORA-14763: Unable to resolve FOR VALUES clause to a partition number
ORA-06512: at line 6