Composition and ValueError: A Circle Made of Coordinate Objects

How can `__init__` refuse to build a Circle at all when the centre you hand it isn't a Coordinate?

Finger exercises

Short drills on what this video just taught. Write the code, run the checks, and reveal the answer only if you are stuck.

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The Circle class below has an empty __init__. Give it a body so that a circle keeps the two things it is handed as the data attributes self.center and self.radius.

Then build one circle: its center sits at x = 3, y = -1, and its radius is the int 5. Assign the circle object to my_circle.

The center has to be a Coordinate object, so work from the inside out — the coordinate must exist before the circle can hold it.
Given code — runs before yours
```
class Coordinate(object):
    """ A coordinate made up of an x and y value """

    def __init__(self, x, y):
        """ Sets the x and y values """
        self.x = x
        self.y = y

    def distance(self, other):
        """ Returns the euclidean distance between two Coordinate objects """
        x_diff_sq = (self.x - other.x) ** 2
        y_diff_sq = (self.y - other.y) ** 2
        return (x_diff_sq + y_diff_sq) ** 0.5
```
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class Circle(object): def __init__(self, center, radius): ... # your code here # Build the circle described above. my_circle = ... # your code here
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⌘/Ctrl + Enter runs
`my_circle` is a `Circle` object
`__init__` stores both arguments on `self`
the center is a `Coordinate` object at the position asked for
the radius is the whole number asked for

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