<p>In python, you can have a function return multiple values.  Here's a contrived example:</p>

<pre><code>def divide(x, y):
    quotient = x/y
    remainder = x % y
    return quotient, remainder  

(q, r) = divide(22, 7)
</code></pre>

<p>This seems very useful, but it looks like it can also be abused ("Well..function X already computes what we need as an intermediate value.  Let's have X return that value also").</p>

<p>When should you draw the line and define a different method?  </p>

Firstly, note that Python allows for the following (no need for the parenthesis):
```
```
q, r = divide(22, 7)
```
```
Regarding your question, there's no hard and fast rule either way. For simple (and usually contrived) examples, it may seem that it's always possible for a given function to have a single purpose, resulting in a single value. However, when using Python for real-world applications, you quickly run into many cases where returning multiple values is necessary, and results in cleaner code.
So, I'd say do whatever makes sense, and don't try to conform to an artificial convention. Python supports multiple return values, so use it when appropriate.