[XML-SIG] unsubscribe
Sara Beakley
SBEAKLEY@uact.edu
Mon, 14 Dec 1998 19:36:51 -0700
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> ----------
> From: John Cowan[SMTP:cowan@locke.ccil.org]
> Sent: Monday, December 14, 1998 2:56 PM
> To: DOM List; xml-sig@python.org
> Subject: Re: [XML-SIG] RE: Equality tests on DOM nodes
>
> Fred L. Drake wrote:
>
> > Typically,
> > two Python objects (let's take lists as an examples) are considered
> > equal if their contents are the same; equality of two objects is not
> > considered to be an unchangable characteristic.
>
> The trouble with that scheme is that it makes equality hard to
> reason about. Intuitively, we expect equality to be transitive,
> (if a = b and b = c then a = c), reflexive (a = a), and symmetrical
> (if a = b then b = a). Making equality depend on mutable properties
> defeats this: a might = b at one time, but a later check for
> b = a might fail.
>
> > a.reverse()
>
> I presume this is a *destructive* reverse (leaves a reversed)?
>
> --
> John Cowan http://www.ccil.org/~cowan cowan@ccil.org
> You tollerday donsk? N. You tolkatiff scowegian? Nn.
> You spigotty anglease? Nnn. You phonio saxo? Nnnn.
> Clear all so! 'Tis a Jute.... (Finnegans Wake 16.5)
>
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<P><FONT COLOR=3D"#0000FF" SIZE=3D2 FACE=3D"Arial">unsubscribe</FONT>
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<P><FONT SIZE=3D2 FACE=3D"MS Sans Serif">----------</FONT>
<BR><B><FONT SIZE=3D2 FACE=3D"MS Sans Serif">From:</FONT></B> =
<FONT SIZE=3D2 FACE=3D"MS Sans Serif">John =
Cowan[SMTP:cowan@locke.ccil.org]</FONT>
<BR><B><FONT SIZE=3D2 FACE=3D"MS Sans Serif">Sent:</FONT></B> =
<FONT SIZE=3D2 FACE=3D"MS Sans Serif">Monday, December 14, 1998 2:56 =
PM</FONT>
<BR><B><FONT SIZE=3D2 FACE=3D"MS Sans Serif">To:</FONT></B> =
<FONT SIZE=3D2 FACE=3D"MS Sans Serif">DOM List; =
xml-sig@python.org</FONT>
<BR><B><FONT SIZE=3D2 FACE=3D"MS Sans Serif">Subject:</FONT></B> =
<FONT SIZE=3D2 FACE=3D"MS Sans =
Serif">Re: [XML-SIG] RE: Equality tests on DOM nodes</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">Fred L. Drake wrote:</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">> Typically,</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">> two Python objects (let's take =
lists as an examples) are considered</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">> equal if their contents are the =
same; equality of two objects is not</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">> considered to be an unchangable =
characteristic.</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">The trouble with that scheme is that =
it makes equality hard to</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">reason about. Intuitively, we =
expect equality to be transitive,</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">(if a =3D b and b =3D c then a =3D =
c), reflexive (a =3D a), and symmetrical</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">(if a =3D b then b =3D a). =
Making equality depend on mutable properties</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">defeats this: a might =3D b at one =
time, but a later check for </FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">b =3D a might fail.</FONT>
</P>
<P><FONT SIZE=3D2 =
FACE=3D"Arial">> =
a.reverse()</FONT>
</P>
<P><FONT SIZE=3D2 FACE=3D"Arial">I presume this is a *destructive* =
reverse (leaves a reversed)?</FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial"> </FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">-- </FONT>
<BR><FONT SIZE=3D2 FACE=3D"Arial">John =
Cowan </FONT><U> <FONT COLOR=3D"#0000FF" =
SIZE=3D2 FACE=3D"Arial"><A HREF=3D"http://www.ccil.org/~cowan" =
TARGET=3D"_blank">http://www.ccil.org/~cowan</A></FONT></U> =
<FONT SIZE=3D2 =
FACE=3D"Arial">cowan@ccil.org</FONT></P>
<P> <FONT SIZE=3D2 =
FACE=3D"Arial">You tollerday donsk? N. You tolkatiff =
scowegian? Nn.</FONT>
<BR> <FONT SIZE=3D2 =
FACE=3D"Arial">You spigotty anglease? Nnn. You phonio =
saxo? Nnnn.</FONT>
<BR> =
<FONT SIZE=3D2 FACE=3D"Arial">Clear all =
so! 'Tis a Jute.... (Finnegans Wake 16.5)</FONT></P>
</UL>
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