I disagree. Maybe its because I grew up learning BASIC, but in-place modification generally confuses and annoys me. Here's an example that I think illustrates one of my issues:
Code version A: a = something b = [a,something_else] c = a.a_method() important_result(b) Code version B: a = something c = a.a_method() b = [a,something_else] important_result(b) ...although I might be confused. What I think would happen is that in version A, under the proposed behavior a would not be modified in- pace, but would be in version B. I can imagine this resulting in some nasty bugs. Am I missing something? Marshall On Sep 27, 8:05 am, "Bill Page" <[EMAIL PROTECTED]> wrote: > On 9/27/07, Jason Grout wrote: > > > > > ... > > > >> where the union function returns the modified graph each time so I can > > >> keep chaining union function calls. The union actually modifies the > > >> graph A, so if you want A left alone and a new graph returned, you do: > > > >> newgraph=A.copy().union(B).union(C).union(D).union(E) > > > >> Comments? Is there a better way to do things? > > > > I would rather union returns a new object rather than modifying A, > > > it's much easier to reason about code that way, and fits better with > > > the rest of SAGE. One could provide a different method to do union in > > > place if one needs. > > > I guess this brings up a much more general issue of conventions in SAGE > > (in general, should methods modify an object in-place or pass back a new > > object?). I'll post up a new thread to try to clarify and get feedback > > on what conventions there are/should be. > > There is another very relevant thread started by Robert Bradshaw on > this list concerning the safety of in-place modifications: > > http://groups.google.com/group/sage-devel/browse_thread/thread/806cd9... > > http://www.sagemath.org:9002/sage_trac/ticket/624 > > In general one wants to do as much in-place modification as possible > without risking unintended side-effects in other parts of the code. > Since Python maintains a reference count for every object, this means > that it is possible for an operation to know whether doing an in-place > modification represents a risk. If there is no external reference to > the object then there is no risk, so the operation should be done > in-place. If the reference count is greater than zero, then the > operation should (automatically) create a copy and then perform the > operation on the copy. Using this convention, for the sake of > efficiency all operations in Sage would be written to operate in-place > but they would transparently create copies of the object as necessary > in order to make side-effects impossible. Thus you can "have your cake > and eat it too". > > Thus in > > newgraph=A.union(B).union(C).union(D).union(E) > > would be done entirely in-place so that 'newgraph' becomes a modified > version of A, while in > > newgraph1=A.union(B).union(C).union(D).union(E) > newgraph2=A.union(B).union(C).union(D).union(E) > > a new copy of A is created and modified before it is assigned to > 'newgraph2'. However we do not have to be aware of this as such. The > only thing we need to remember is that there can be no side-effects. > > Regards, > Bill Page. --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
