Chapter 6. Fruitful Functions
Many of the Python functions we have used, such as the math functions, produce return values. But the functions we’ve written are all void: they have an effect, like printing a value or moving a turtle, but they don’t have a return value. In this chapter you will learn to write fruitful functions.
Calling the function generates a return value, which we usually assign to a variable or use as part of an expression.
e = math.exp(1.0) height = radius * math.sin(radians)
The functions we have written so far are void. Speaking casually, they have no return value; more precisely, their return value is
In this chapter, we are (finally) going to write fruitful functions. The first example is
area, which returns the area of a circle with the given radius:
def area(radius): a = math.pi * radius**2 return a
We have seen the
return statement before, but in a fruitful function the
return statement includes an expression. This statement means: “Return immediately from this function and use the following expression as a return value.” The expression can be arbitrarily complicated, so we could have written this function more concisely:
def area(radius): return math.pi * radius**2
On the other hand, temporary variables like
a can make debugging easier.
Sometimes it is useful to have multiple return statements, one in each branch of a conditional:
def absolute_value(x): if x < 0: return -x else: return x
return statements are in an alternative ...