Favorite non-python language trick?

[Joseph Garvin]

As someone who learned C first, when I came to Python everytime I read
about a new feature it was like, "Whoa! I can do that?!" Slicing, dir(),
getattr/setattr, the % operator, all of this was very different from C.

I'm curious -- what is everyone's favorite trick from a non-python
language? And -- why isn't it in Python?

Here's my current candidate:

So the other day I was looking at the language Lua. In Lua, you make a
line a comment with two dashes:

-- hey, this is a comment.

And you can do block comments with --[[ and ---]].

--[[
hey
this
is
a
big
comment
--]]

This syntax lets you do a nifty trick, where you can add or subtract a
third dash to change whether or not code runs:

--This code won't run because it's in a comment block
--[[
print(10)
--]]

--This code will, because the first two dashes make the rest a comment,
breaking the block
---[[
print(10)
--]]

So you can change whether or not code is commented out just by adding a
dash. This is much nicer than in C or Python having to get rid of """ or
/* and */. Of course, the IDE can compensate. But it's still neat :)

[Steve Jorgensen]

On 24 Jun 2005 19:09:05 +0400, Sergei Organov <os*@javad.ru > wrote:

Steven D'Aprano <st***@REMOVETH IScyber.com.au> writes:

On Fri, 24 Jun 2005 00:55:38 -0600, Joseph Garvin wrote:

> I'm curious -- what is everyone's favorite trick from a non-python
> language? And -- why isn't it in Python?
Long ago, I used to dabble in Forth. You could say, the entire Forth
language was a trick :-) It was interesting to be able to define your own
compiler commands, loop constructs and so forth.

One of the things I liked in Pascal was the "with" keyword. You could
write something like this:

with colour do begin
red := 0; blue := 255; green := 0;
end;

instead of:

colour.red := 0; colour.blue := 255; colour.green := 0;

Okay, so maybe it is more of a feature than a trick, but I miss it and it
would be nice to have in Python.

... that quickly becomes quite messy:

- When abused -
with A do begin
.....
with B do begin
.....
with C do begin
x := y;
end;
end;
end;

Like many features that can be helpful when used well, and harmful when used
poorly, it's not a simple question whether it should be in any given language.
It also makes sense to consider whether other features already in the language
can fill the same need (though I don't know Python well enough to address that
yet). Even though I like "With" in VB and use it often, I always consider its
use a warning that perhaps that code should be factored into the class
somehow.

[GodFoca]

> if a.value == True:

return a if not database.connec t == error:
database.query( q)
Yeah, yeah, I know that :-)
What I mean is that most of the time I find the code more "readable" (I
know that more readable code ain't better code, but it helps when you
work with other people...).
"unless" seems to become "while not", as opposed to "if not". Should be
more consistent.

My mistake :-S
The comment in the code was erroneous, I shouldn't write messages to
the list while asleep ^_^

'unless' works as 'if not', not as 'while not'. Sorry for that :-)

Anyway, it does improve readability. I know that it doesn't necessarily
makes code better, but it's a nice "trick" that I like :-)

Other nice thing about ruby is declaring regexps as /regexp/ rather
than having to re.compile("reg exp"), and having a built-in operator to
match against them (of course, as everything in ruby, overloadable in
each class :-))

-NIcolas

[Mike Meyer]

Tom Anderson <tw**@urchin.ea rth.li> writes:

On Fri, 24 Jun 2005, Roy Smith wrote:

Tom Anderson <tw**@urchin.ea rth.li> wrote:

The one thing i really do miss is method overloading by parameter
type. I used this all the time in java

You do things like that in type-bondage languages

I love that expression. I think it started out as 'bondage and
discipline languages', which is even better. I'm going to start
referring to python as a 'sluttily typed' language.

Since the user is the one bound with B&D languages, they are clearly
tops. Which makes Python a bottom.

<mike
--
Mike Meyer <mw*@mired.or g> http://www.mired.org/home/mwm/
Independent WWW/Perforce/FreeBSD/Unix consultant, email for more information.

[Ivan Van Laningham]

Hi All--

Mike Meyer wrote:

Since the user is the one bound with B&D languages, they are clearly
tops. Which makes Python a bottom.

Well, we certainly hope Python has a safe word.

Metta,
Ivan
----------------------------------------------
Ivan Van Laningham
God N Locomotive Works
http://www.andi-holmes.com/
http://www.foretec.com/python/worksh...oceedings.html
Army Signal Corps: Cu Chi, Class of '70
Author: Teach Yourself Python in 24 Hours

[Mandus]

Sun, 26 Jun 2005 08:35:58 +0200 skrev Peter Otten:

Steven D'Aprano wrote:

On Sat, 25 Jun 2005 21:30:26 +0200, Peter Otten wrote:

Mandus wrote:

By using the builtin reduce, I
move the for-loop into the c-code which performs better.

No. There is no hope of ever writing fast code when you do not actually
measure its performance.
Good grief! You've been spying on Mandus! How else could you possibly know
that he doesn't measure performance? Are you running a key-logger on his
machine? *wink*

His mentioning reduce() as a performance panacea was a strong indication
even without looking over his shoulders. He filled in some conditions in a
later post, but "[u]sing reduce ... performs better [than a for-loop]" is
just wrong.

Ok - so sometimes reduce() for convenience (nha, that's just me...),
sometimes for performance. In some cases clever use of map/reduce/etc.
have given a good speedup - say 4 times that of for-loops. But going to
C can give 10 to 100 times speed up over that again... So it depends how
important the performance is. Going to C/Fortran is always a bit more
hassel, while reduce is something you can stick in your interactive
session to finish the work rather before than after lunch :)

[snip]

Isn't it reasonable to just say, "I use join because it is faster than
adding strings" without being abused for invalid optimization?
OK, I am making a guess: "".join(strings ) is more often faster than
naive string addition than reduce() wins over a for-loop.

you're probably right.
I don't think my pointed comment qualifies as "abuse", by the way.

neither think I.
--
Mandus - the only mandus around.

[Paddy]

Joseph Garvin wrote:
'm curious -- what is everyone's favorite trick from a non-python
language? And -- why isn't it in Python?

I use constraints programming at work, Check out "System Verilog" or
OZ/Mozart.

It would be great if this style of programming could be added to
Python.

It is a declarative programming style
(http://en.wikipedia.org/wiki/Declarative_programming), in which you
can state what discrete values constrained values can take , say in a
list. Give a set of functions that must be true for the variables then
sit back and generate one or many sets of variable values that fit the
constraints.

The OZ homepage has an example for solving the eight queens problem:

http://www.mozart-oz.org/documentati...scripts.queens

My use would be for testing. In the electronic design automation
fields, there are several proprietary languages with this feature, here
is an example written in Cadence's Specman 'e' language:
http://www.asic-world.com/specman/specman_one_day2.html
Cheers, Paddy.

[Terry Reedy]

"Paddy" <pa*******@nets cape.net> wrote in message
news:11******** *************@g 44g2000cwa.goog legroups.com...

The OZ homepage has an example for solving the eight queens problem:

Buried in the generator test module (something like
lib/test/test_generators .py) are solutions for both 8Queens and Knight's
Tour. You might find these of interest.

Terry J. Reedy

[Paddy]

Sadly, its not a solution that I'm after, but a particular toolkit that
can be used for solving that type of problem.

- Pad.

[Brian Elmegaard]

Joseph Garvin <k0*****@kzoo.e du> writes:

I'm curious -- what is everyone's favorite trick from a non-python
language?
Metapost solution of linear equations:
x1+9=x2-8=2;
And -- why isn't it in Python?

I'd like to know too.

--
Brian (remove the sport for mail)
http://www.et.web.mek.dtu.dk/Staff/be/be.html

[Terry Hancock]

On Wednesday 29 June 2005 10:51 pm, Paddy wrote:

Joseph Garvin wrote:
'm curious -- what is everyone's favorite trick from a non-python
language? And -- why isn't it in Python?

I use constraints programming at work, Check out "System Verilog" or
OZ/Mozart.

It would be great if this style of programming could be added to
Python.

Check out:
http://www.logilab.org/projects/python-logic/

In short, it has been already.

This is something pretty new to me, so I can't comment on how well
it would meet your expectations, but I see now that the site does mention
OZ/Mozart as comparables.

--
Terry Hancock ( hancock at anansispacework s.com )
Anansi Spaceworks http://www.anansispaceworks.com