raw strings and \

[plahey]

I thought I understood raw strings, then I got bitten by this:

x=r'c:\blah\'

which is illegal! I thought that \ had no special meanning in a raw
string so why can't it be the last character?

making me do:

x=r'c:\blah' '\\'

is just silly...

[Steve Holden]

pl****@alumni.c altech.edu wrote:

Hi,

thanks for the reply. I was not aware of this in raw strings (and
frankly, don't like it... but who cares about that :-) )
Healthy attitude!
When I needed embedded quotes in a raw string I went the triple quote
route:

a = r'''check \' this'''

which makes more sense to me.

But remember you could equally well have used

a = "check \\' this"

I presume you do *want* that backslash in there? If not, of course, then

a = "check ' this"

is by far the simplest way to represent what you want. because Python
offers four different string quotes, each of which can be raw, there's
always a way ...

regards
Steve
--
Steve Holden [phone] [phone]
Holden Web LLC/Ltd www.holdenweb.com
Love me, love my blog holdenweb.blogs pot.com

[plahey]

>Alas, somebody will now quote Emerson at you, I fear;-).

Let them come :-)

I almost always see this (mis)quoted as:

"consistenc y is the hobgoblin of little minds"

which is not really what Emerson said. The full quote is:

"A foolish consistency is the hobgoblin of little minds"

I would say that a foolish anything is something to avoid. I don't
think that anyone would claim that inconsistency is a virtue in a
computer language (or in anything else for that matter).

[Blackbird]

Slightly OT, but here is a crazy little program that shows the power of
using raw strings:

s=r'print "s=r\'%s\'\n%s" %(s,s)'
print "s=r\'%s\'\n%s" %(s,s)

When run, this program will print an exact copy of itself.

Blackbird

[Steven D'Aprano]

Almost off-topic.

Well, okay, completely off-topic.

On Sun, 05 Mar 2006 19:47:07 -0800, plahey wrote:

I would say that a foolish anything is something to avoid. I don't
think that anyone would claim that inconsistency is a virtue in a
computer language (or in anything else for that matter).

Inconsistency can be a virtue whenever predictability is a vice.

Imagine, for example, that Fred and Bill are negotiating over something
(say, Fred wants to buy Bill's house). If Fred is predictable, then Bill
can work out just how high Fred is willing to pay, and refuse to accept a
penny less. In other words, if you are too consistent, people will learn
to take advantage of that consistency to get the most from you for the
least in return.

On the other hand, if Fred is unpredictable -- that is, inconsistent -- it
is much harder to predict his behaviour, and Bill will be more cautious
and more likely to settle for a lower offer.

Think about hostile negotiations. If people know exactly how far they
can push you before you will get mad, they will push right to the edge.
But if they don't know where that edge lies, if they are uncertain how you
will react ("if I demand the Sudetenland, will he break off negotiations
and launch a preemptive attack?"), they will be more cautious, less
demanding, more open to compromise.

Cognitive scientists believe that the benefits of unpredictabilit y and
inconsistency are behind the evolution of such irrational emotions as
jealousy and rage. In that sense, their very irrationality is what makes
them rational.
--
Steven.

[Fredrik Lundh]

"Blackbird" <fa**@nospam.no > wrote:

Slightly OT, but here is a crazy little program that shows the power of
using raw strings:

s=r'print "s=r\'%s\'\n%s" %(s,s)'
print "s=r\'%s\'\n%s" %(s,s)

When run, this program will print an exact copy of itself.

I'm not sure what the raw strings brings to the table, though; it's not like you need
them to write a "self-replicating" python program:

http://miscoranda.com/37

</F>

[Blackbird]

Fredrik Lundh wrote:

"Blackbird" <fa**@nospam.no > wrote:

Slightly OT, but here is a crazy little program that shows the power
of using raw strings:

s=r'print "s=r\'%s\'\n%s" %(s,s)'
print "s=r\'%s\'\n%s" %(s,s)

When run, this program will print an exact copy of itself.

I'm not sure what the raw strings brings to the table, though; it's
not like you need them to write a "self-replicating" python program:

http://miscoranda.com/37

Great link! I wasn't aware that this was called a Quine. This one is
great:

_='_=%r;print _%%_';print _%_

When I hacked down the two lines, I didnt see that assigning the variable to
the beginning of the program, instead of the end, essentially gets rid of
literals in the actual print statement. And now I also learned about %r.

[Fredrik Lundh]

pl****@alumni.c altech.edu wrote:

I guess my point is that it is quite surprising that r'\' is not a
legal way to represent a backslash. I look for consistency in the
tools that I work with and this except-for-the-last-character exception
is annoying

you seem to be missing that "exception" you think you're seeing is
the consequence of a consistency: *all* literal strings are parsed
in the same way, no matter what's prefix qualifier they're using.

</F>

[John Salerno]

Alex Martelli wrote:

Now get back to work on your new Nutshell book :-)

Yep, good point!-)

Are you working on a new edition? I didn't see any new Python books
listed on O'Reilly's site through April, but I'd definitely be
interested in new versions of the books I plan to get soon (Cookbook and
Nutshell, for example, although I figure the Cookbook is fairly new at
this point.)

[plahey]

Interesting, so thats where this comes from.

Of course the problem is that I thought that a raw string was a
different animal than a regular string (i.e. truely "raw" where no
characters are special, except of course the closing quote) so parsing
consistency is surprising to an end user (who has an overly-simplistic
mental model).

I'm sure that this choice greatly simplifies the internals of Python.
As an end user, of course, I couldn't care less about this (just as my
end users don't care about my problems :-) ). I would still prefer my
still-bloody raw strings, but I can live with the slightly-cooked ones
now that I've got it...

Thanks!

[Alex Martelli]

John Salerno <jo******@NOSPA Mgmail.com> wrote:

Alex Martelli wrote:

Now get back to work on your new Nutshell book :-)

Yep, good point!-)

Are you working on a new edition? I didn't see any new Python books
listed on O'Reilly's site through April, but I'd definitely be
interested in new versions of the books I plan to get soon (Cookbook and
Nutshell, for example, although I figure the Cookbook is fairly new at
this point.)

Yep, a 3rd edition of the Cookbook is not in the cards. A 2nd edition
of the Nutshell is, and if all goes well should be out before the fall.
Alex