Question

If I have a class such as below (only with many more properties), is there are clean way to note which fields are required before calling a particular method?

class Example():

    def __init__(self):
        pass

    @property
    """Have to use property methods to have docstrings..."""
    def prop1(self):
        return self._prop1
    @prop1.setter
    def task(self, value):
        # validation logic..
        self._prop1 = value

    def method(self):
        # check all required properties have been added

I could write an array by hand of all required propeties and loop through them in a method, but I was wondering if there is a cleaner way for example by implementing a @requiredProperty descriptor.

The class is used to generate a POST request for a web API. The request has 25+ parameters, some of which are required and some optional.

Rather than on the method calling the request having to loop through an array such as:

required_props = ['prop1','prop2',....]

I was hoping there was a way in Python of adding a required decorator to properties so I wouldn’t have to keep track by hand. E.g.

    @property, @required
    def prop1(self):
        return self._prop1

Answer 1

This should work the same way as in any OO language: A required property must be set during construction time. Calling the objects methods must never leave the object in a “bad” state, so that method can be called on any constructed object.

If the above doesn’t hold true, you should think about refactoring your code.

Of course it is always possible to alter a python object to not be valid anymore by poking around in its guts. You don’t do that unless you have a good reason. Don’t bother checking for this, as your program should just blow up in your face whenever you do something stupid so you learn and stop.