A function can only have one return value, but quite often you want to return multiple items as the result of a function. To work with the single return value, we simply return a container such as a tuple, a list, or a dictionary with the items you want to return. For instance, returning four coordinates describing the bounding box of a polygon, we can return a tuple with the four coordinates. Python has a useful mechanism to help with unpacking this single return value 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 (12, 3, 2, 2) assigned to t, instead of writing:
t = (12, 3, 2, 2)
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: 12Or as a dictionary, which can also provide some dynamic insights into calculated results to help control the flow:
def computeBoundingBox(x):
if x==1:
return {'top':12, 'left':3,' bottom':41, 'right':32, 'success':True}
else:
return {'top':12, 'left':3, 'bottom':41, 'right':32, 'success':False}
bbox = computeBoundingBox(1) # returns the result as a dictionary
if bbox.get('success'): # if the process succeeds
print(bbox['top']) # output: 12