Hi there I need to schedule a flow to run the first Wednesda

Question

Hi there I need to schedule a flow to run the first Wednesday of every month I tried the approach outlined <https prefect community slack com archives CL09KU1K7 p1600170685303800|here> and then ran into the same issue described in the thread Is it possible to do this with the existing filters I don t understand the security implications of allowing arbitrary callbacks for functions but it seems like a good feature to have

Pedro Machado · Answer

I was trying to use this logic ```def is first wednesday dt first wednesday = dt start of month next pendulum WEDNESDAY return dt == first wednesday clock = clocks CronClock 0 0 3 schedule = Schedule clocks= clock filters= is first wednesday ``` but I got ``` raise ValidationError Invalid function reference format value marshmallow exceptions ValidationError Invalid function reference lt function is first wednesday at 0x7fa0e2768ee0 gt ```

Chris White · Answer

Hi Pedro all schedules filters need to be executable in Prefect Cloud hence the tight restriction that they must come from the pre defined library We definitely welcome new filter contributions if they are general flexible enough `is first weekday of month day of week int ` could be a nice one to PR In the meantime because your schedule description only consists of 12 dates that span the year I recommend using an explicit list + a `DatesClock` as described in this similar issue <https github com PrefectHQ prefect issues 3501>

Pedro Machado · Answer

Thanks Chris I ll give this a try