PrintIt happens quite often that you want to hand back different things as the result of a function, for instance four coordinates describing the bounding box of a polygon. But a function can only have one return value. It is common practice in such situations to simply return a tuple with the different components you want to return, so in this case a tuple with the four coordinates. Python has a useful mechanism to help with this by allowing us to assign the elements of a tuple (or other sequences like lists) to several variables in a single assignment. Given a tuple t = (12,3,2,2), instead of writing
top = t[0] left = t[1] bottom = t[2] right = t[3]
you can write
top, left, bottom, right = t
and it will have the exact same effect. The following example illustrates how this can be used with a function that returns a tuple of multiple return values. For simplicity, the function computeBoundingBox() in this example only returns a fixed tuple rather than computing the actual tuple values from a polygon given as input parameter.
def computeBoundingBox():
return (12,3,41,32)
top, left, bottom, right = computeBoundingBox() # assigns the four elements of the returned tuple to individual variables
print(top) # output: 12
This section has been quite theoretical, but you will often encounter the constructs presented here when reading other people’s Python code and also in the rest of this course.