Function returning a tuple or None: how to call that function nicely?

Question

Suppose the following:

def MyFunc(a):
  if a < 0:
    return None
  return (a+1, a+2, a+3)

v1, v2, v3 = MyFunc()
# Bad ofcourse, if the result was None

What is the best way to define a function that returns a tuple and yet can be nicely called. Currently, I could do this:

r = MyFunc()
if r:
  v1, v2, v3 = r
else:
  # bad!!
  pass

What I don't like about this is that I have to use a single variable and then unpack it.

Another solution is I could have the function return a tuple full of Nones so that the caller can nicely unpack....

Anyone can suggest a better design?

Answer 1

How about raise an ArgumentError? Then you could try calling it, and deal with the exception if the argument is wrong.

So, something like:

try:
    v1, v2, v3 = MyFunc()
except ArgumentError:
    #deal with it

Also, see katrielalex's answer for using a subclass of ArgumentError.

Answer 2

This should work nicely:

v1, v2, v3 = MyFunc() or (None, None, None)

When MyFunc() returns a tuple, it will be unpacked, otherwise it will be substituted for a 3-tuple of None.