TypeError: not all arguments converted during string formatting sql binding

Question

I have written an object to connect and execute my Snowflake queries:

class snowflake_conn(object):
    #some other methods...
    
    #execute method
    def execute(self, sql, bindvars=None):
        try:
            if bindvars is None:
                self.cursor.execute(sql)
            else:
                self.cursor.execute(sql, bindvars)
        except Exception:
            raise

Then I tried binding the variables:

conn.execute("""
with result as (select * from db.schema.tbl where transaction_date >= :1 or delivery_date >= :1)
select * from result
""", (last_month_date,))

It keeps giving me error TypeError: not all arguments converted during string formatting. I followed the binding variables here: https://docs.snowflake.com/en/user-guide/python-connector-example.html#binding-data

I have tried using ? and adding extra (last_month_date, last_month_date) to no avail. Any idea how I could fix this would be much appreciated.

Thank you beforehands.

Edit: added trailing comma in the binding and still same error.