[Python-ideas] set.add() return value

Terry Reedy tjreedy at udel.edu
Tue Feb 17 16:39:37 CET 2009

Steven D'Aprano wrote:

> I'm with Raymond on this.

Me too.  Some languages return self from mutating methods (allowing 
chaining).  Python's builtins and stdlib consistently (afaik) returns 
None (preventing chaining).  Returning True or False depending on 
whether a mutation was done seems like an innovation.  It is an 
intriguing idea, but doing so just occasionally would add mental burden. 
  Why now change list.extend()? (False if the extension is empty.) or 
list.sort() (False if the list is already sorted.)  List.append(), of 
course, would always return True.

Of course, in Python, having *any* consistent return other than None is 
difficult because much mutation is done thru special methods wrapped in 


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