你如何检查用户是否至少传递了一个参数？

Question

Sometimes an object can be constructed by different types of arguments. For example, a circle object can be defined either by providing its radius or its circumference. How do I write the __init__ method so that it constructs a circle object both when the user enters a radius and when they enter a circumference.

I came up with this but it looks too bloated:

class Circle:

    def __init__(self, radius = None, circumference = None):

        # Calculate area when user provides circumference
        if radius is None and circumference is not None:
            self.area = (circumference**2) / (4*3.14)

        # Calculate area when user provides radius
        elif radius is not None and circumference is None:
            self.area = (radius ** 2) * 3.14

        # Raise error if neither radius nor circumference or both are provided
        else:
            raise TypeError("Pass either a radius or circumference argument value")

Do you default the parameters to None or is there a proper Python way designed for this scenario?

Also, is the use of TypeError correct in this case?

I don't even know if radius and circumference are considered optional or required arguments here since at least one of them is somehow required. Can someone enlighten me please?

Answer 1

I would just prioritize one of both arguments if two are provided. It would be something like this:

class Circle:

    def __init__(self, radius = None, circumference = None):

        # Calculate area when user provides circumference
        if circumference:
            self.area = (circumference**2) / (4*3.14)

        # Calculate area when user provides radius
        elif radius:
            self.area = (radius ** 2) * 3.14

        # Raise error if neither radius nor circumference or both are provided
        else:
            raise TypeError("Pass either a radius or circumference argument value")

Answer 2

Assuming, you want the the title question answered:

Your code seems fine, but you could use **kwargs parameter instead of listing all possible candidates, which can be checked for containing something easily without going into details.

For the general approach:

I guess your breakdown of functionality adds to complexity: why do the computation stuff in the constructor? Consider this interface:

   c = Circle()
   c.setRadius(4.5) # alternatively: c.setCircumference(13.7)
   print(c.getArea())