How to dynamically call functions in python from a string value?

Question

I'm trying to use the following library (dbader/schedule) to schedule tasks and I'm trying to call some of the methods on the class dynamically from string values.

I have an object that comes back from a database that looks like the following:

{
  "scheduled_interval": "wednesday",
  "scheduled_time": "11:00",
  "tags": ["tag1"]
}

I am trying to achieve something like the following, but calling the functions programatically whereby the func call in bold is driven by the database value scheduled_interval:

schedule.every().wednesday.at("11:00").tags(["tag1"])

I tried using getattr as can be seen below, but i'm unsure as to how I can chain the calls in a way that doesn't include many nested getattr calls:

def add_to_schedule(task: Task):
    job = schedule.every()
    # Below should be equivalent to schedule.every().wednesday()
    job_1 = getattr(job, task.scheduled_interval)()
    job_2 = getattr(job_1, "at")
    # Below should be equivalent to schedule.every.wednesday().at("11:00")
    job_2(task.scheduled_time)

f = getattr(schedule.every, "wednesday") should get you the wednesday method of schedule.every. — Tom Dalton
– Tom Dalton, Commented Apr 18, 2021 at 13:00

fed_tf · Accepted Answer · 2021-04-18 13:27:44Z

1

You could extend operator.methodcaller by wrapping it with a function like this:

from operator import methodcaller


def chainmethodcaller(obj, calls): 
    for call in calls: 
        obj = methodcaller(*call)(obj)
    return obj

And use it like this

chainmethodcaller(
    schedule,
    [('every',), ('wednesday',), ('at', '11:00'), ('tags', ["tag1"])]
)

Feel free to add a few conditions if you don't want to pass iterables for methods without arguments.

answered Apr 18, 2021 at 13:27

fed_tf

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