On Nov 25, 2007, at 1:34 PM, William Stein wrote: > On Nov 25, 2007 12:13 PM, Nick Alexander <[EMAIL PROTECTED]> > wrote: >> Hi William, >> >> I've been thinking about >> >> http://sagetrac.org/sage_trac/ticket/1135 >> >> for about 2 days now. I can think of no obvious way to handle the >> following three cases: >> >> R.<x, y> = PolynomialRing(ZZ) # names should be added >> R.<x, y> = PolynomialRing(ZZ, 'x, y') # names should not be added >> R.<x, y> = PolynomialRing(ZZ, 'a, b') # names should not be added >> >> smoothly. In general, deciding whether the caller has included names >> is equivalent to the halting problem. Due to Python's line-as-block >> syntax, preprocessing *cannot add newlines*, making it essentially >> impossible to add try/except blocks. (I've tried -- if it works at >> the prompt, it fails in doctests.) >> >> What I think we should do is process "R.<x, y> = PolynomialRing >> (ZZ)" to >> >> with __default_var_context('x, y'): R = PolynomialRing(ZZ); (x, y, ) >> = R._first_ngens(2); >> >> And then have normalize_names in parent_gens.pyx check to see if >> there is a default var context in place when creating a ring with no >> names specified. This would let "R.<x, y> = PolynomialRing(ZZ, 'a, >> b')" be handled uniformly. >> >> The only reason to use with: rather than just assignment is that it >> is possible to guarantee default variable names do not remain in >> scope too long. >> >> Thoughts? >> Nick >> >> PS. I'll try a quick implementation soon, but I don't want to waste >> time if there is some reason this is a bad idea. > > If this works I think it would be an extremely good idea. I can't > see a problem with it yet. Though implementing it could suggest > problems. > > It also relates to some people's desire to have a mechanism for having > a default variable name, e.g., always use "x" or "x0,x1,x2,..." if > nothing is specified.
+1 I think this is a great way to solve the problem. - Robert --~--~---------~--~----~------------~-------~--~----~ 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/ -~----------~----~----~----~------~----~------~--~---
