On 25 Apr., 08:10, Robert Bradshaw <rober...@math.washington.edu> wrote: > On Apr 23, 2010, at 7:07 PM, Nathan O'Treally wrote: > > The Tutorial (http://www.sagemath.org/doc/tutorial/ > > programming.html#loops-functions-control-statements-and-comparisons) > > gives another example: > > sage: GF(5)(1) == QQ(1); QQ(1) == GF(5)(1) > > False > > False > > sage: GF(5)(1) == ZZ(1); ZZ(1) == GF(5)(1) > > True > > True > > sage: ZZ(1) == QQ(1) > > True > > # This means a==b is False and a==c is True though c==b *is* True: > > sage: a=GF(5)(1) > > sage: b=QQ(1) > > sage: c=ZZ(1) > > # (scroll away these definitions to surprise somebody else) > > sage: a==b , b==c , c==a > > (False, True, True) > > sage: b==a , c==b , a==c > > (False, True, True) > > # HELL! 8/ > > (The tutorial warns in contrast to Sage it *is* consistently defined > > in Magma.) > > > a := GF(5)!1; > > b := GF(7)!1; > > c := 1; > > > a eq c; > true > > b eq c; > true > > a eq b; > > >> a eq b; > ^ > Runtime error in 'eq': Arguments are not compatible > Argument types given: FldFinElt, FldFinElt > > In Python, the convention is that == and != never raise an error, so > False is returned if coercion fails (the two domains are incompatible).
sage: a=GF(5)(1) sage: b=QQ(1) sage: a==b False sage: a!=b # This then should return False because the coercion failed True # Ouch! Otherwise one could test with (a==b or a!=b)==False if the coercion failed (like NaN==NaN is always false). -Leif -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
