6.10. Composition¶
As we have already seen, you can call one function from within another. This ability to build functions by using other functions is called composition.
As an example, we’ll write a function that takes two points, the center of the circle and a point on the perimeter, and computes the area of the circle.
Assume that the center point is stored in the variables xc
and yc
, and
the perimeter point is in xp
and yp
. The first step is to find the
radius of the circle, which is the distance between the two points.
Fortunately, we’ve just written a function, distance
, that does just that,
so now all we have to do is use it:
radius = distance(xc, yc, xp, yp)
The second step is to find the area of a circle with that radius and return it. Again we will use one of our earlier functions:
result = area(radius)
return result
Wrapping that up in a function, we get:
We called this function area2
to distinguish it from the area
function
defined earlier. There can only be one function with a given name within a
module.
Note that we could have written the composition without storing the intermediate results.
def area2(xc, yc, xp, yp):
return area(distance(xc, yc, xp, yp))