Terry Reedy wrote:

Alexander Belopolsky wrote:

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Terry Reedy wrote:

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I had exactly the same idea, but did not post because it violates the general rule that mutators return None.

Is there such a rule? What about set/dict pop?

The rule perhaps should be restated as 'Collection mutators return None or possible an item but not the collection.'

And to clarify the rationale for that guideline: it is to make it clear that the mutator is changing the container in place and *not* creating a new container object.

myset.pop() # No new container, returns popped object mylist.sort() # No new container, returns None sorted(mylist) # New container, so return it mystr.lower() # Creates new string, so return it

Cheers, Nick.