Writing Django Func() Expression with multiple parameters and specify the order

I'm using Func() Expressions to use this answer and compute the difference between two dates in business days:

class BusinessDaysBetween(Func):
    """Implementation of a Postgres function to compute the working holidays between two fields."""
    template = """
        (SELECT COUNT(*) FROM generate_series(%(expressions)s, interval '1 day') s(day)
        WHERE EXTRACT(DOW FROM s.day) NOT IN (0, 6))
    """
    arity = 2
    output_field = IntegerField()

However, I am having problems with the formatting of Date and DateTime. So I want to call the functions mentioned in this answer.

My edited code looked like this:

class BusinessDaysBetween(Func):
    """Implementation of a Postgres function to compute the working holidays between two fields."""
    template = """
        (
            SELECT COUNT(*) FROM generate_series(
                TO_CHAR(CAST(%(expressions)s AS DATE), 'YYYY-MM-DD'),
                TO_CHAR(CAST(%(expressions)s[1] AS DATE), 'YYYY-MM-DD'),
                interval '1 day'
            ) s(day)
            WHERE EXTRACT(DOW FROM s.day) NOT IN (0, 6)
        )
    """
    arity = 2
    output_field = IntegerField()

The problem is that I am putting both parameters in the first place, I don't know how to specify the order of the parameters in which they will appear. I already tried:

• With {0} and {1} and it says there is a syntax error.
• %(expressions)s and %(expressions)s[1] and nothing.
• With %s, it's raising the "not enough arguments for format string" error.

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