Duncan Booth wrote: > "Virgil Dupras" <[EMAIL PROTECTED]> wrote: > >> I think I see what Marcin means. The 'node' is changed too fast in the >> chain, and next is assigned to 'nextnode' instead of being assigned to >> node. > > I can see why Marcin was confused. Many other languages assignment is an > expression, so a=b=c is simply a=(b=c). In Python it isn't an expression, > the chained assignment is a specific part of the syntax, so (as with > chained comparisons) the semantics may be surprising to the uninitiated. > > As a matter of interest do PyLint or PyChecker check for this situation > (chained assignment where the target of an assignment is also a > subexpression of a later assignment)? > Where's the published syntax for chained assignment?
> Also it may be worth noting that unpacking has a similar behaviour: > > node, node.next = nextnode, nextnode > > has the same result as the chained assignment: the RHS is a tuple and is > fully evaluated before the assignment, but the LHS is not a tuple and the > assignment happens strictly left to right with each assignment fully > completed before proceeding to the next one. > Well that is explained (albeit badly) in the reference manual: """An assignment statement evaluates the expression list (remember that this can be a single expression or a comma-separated list, the latter yielding a tuple) and assigns the single resulting object to each of the target lists, from left to right.""" That wording appears to be a rather bad mix of factoids from unpacking and chained assignment. Is it just me, or does this whole section need a rewrite? regards Steve -- Steve Holden +44 150 684 7255 +1 800 494 3119 Holden Web LLC/Ltd http://www.holdenweb.com Skype: holdenweb http://del.icio.us/steve.holden Recent Ramblings http://holdenweb.blogspot.com -- http://mail.python.org/mailman/listinfo/python-list
