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 :)

[Steven D'Aprano]

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.
--
Steven

[Claudio Grondi]

I supose it will be very, very hard to find a trick
which turns out useful in Python. The current
set of features is from my point of view very
well designed out of the experience with many
other languages, so maybe you can use Python
as reference telling you which tricks are really
useful in programming and which are just bad,
non-Pythonic style.

At least I am myself out of ideas, else I had
proposed a PEP already, to get it or have
provided a module for it.

So feel free to poke around with Python.

if(not \
"--[[" == "--[["):
# block of code
# --]]
as (already suggested) will also do the
trick with the block comment.

By the way, I personally find
--[[
good style comment block
]]--
or
[[--
good style comment block
--]]
much more intuitive than
--[[
bad style comment block
--]]

Claudio
"Joseph Garvin" <k0*****@kzoo.e du> schrieb im Newsbeitrag
news:ma******** *************** *************** @python.org...

Claudio Grondi wrote:

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

I am very happy not to have such "tricks" in Python.

Any other (useful) suggestions?

Claudio

I'm glad and all that not everyone shares my enthusiasm over Lua's
trick, and I'm glad that C/C++ can do it, but the original issue was
non-python language tricks in general. Lets keep the thread on track.

So far we've got lisp macros and a thousand response's to the lua trick.
Anyone else have any actual non-python language tricks they like?

Yeesh.

"Joseph Garvin" <k0*****@kzoo.e du> schrieb im Newsbeitrag
news:ma******* *************** *************** *@python.org...

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 :)

[utabintarbo]

>with colour do begin

red := 0; blue := 255; green := 0;
end;

instead of:

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

Why not:

from color import *

red := 0
blue := 255
green := 0

....

[Steven D'Aprano]

On Fri, 24 Jun 2005 06:13:00 -0700, utabintarbo wrote:

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

instead of:

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

Why not:

from color import *

red := 0
blue := 255
green := 0

Because colour is not a module, it is a record. Sorry, I assumed that
people would be familiar with Pascal records (similar to C structs) and
it wouldn't need explanation. My bad :-(

The closest example in Python would be:

def class Colour:
def __init__(self, blue=0, green=0, red=0):
self.blue = blue
self.green = green
self.red = red

which would become something like:

def class Colour:
def __init__(self, blue=0, green=0, red=0):
# pseudo-Python code borrowing concept "with" from Pascal
with self:
blue = blue
green = green
red = red

And now you can see why Python doesn't support this idiom.

--
Steven.

[D H]

Joseph Garvin wrote:

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

You can try out new features yourself now using various python
extensions or descendants:
http://livelogix.net/logix/
- macros, no statement/expression distinction
http://students.ceid.upatras.gr/~sxanth/pyc/
- assignments are expressions, you can try other features never added
python like a ternary operator (x ? true action:false action)
http://boo.codehaus.org/
assignments are expressions, macros, static typing, no more "self"
required, ...

[Peter Hansen]

ut*********@gma il.com wrote:

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

instead of:

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

Why not:
from color import *

red := 0
blue := 255
green := 0

What do you think this actually does?

It doesn't do anything remotely resembling either of the things quoted
above. In fact, the "from color import *" line is pretty much useless here.

-Peter

[infidel]

> def class Colour:

def __init__(self, blue=0, green=0, red=0):
# pseudo-Python code borrowing concept "with" from Pascal
with self:
blue = blue
green = green
red = red

And now you can see why Python doesn't support this idiom.

Maybe it would make more sense if it was done a la Visual Basic

with self:
.blue = blue
.green = green
.red = red

requiring a dot to be typed removes the ambiguity and gives the IDEs a
chance to Intellisense-ify your coding.

[D H]

infidel wrote:

def class Colour:
def __init__(self, blue=0, green=0, red=0):
# pseudo-Python code borrowing concept "with" from Pascal
with self:
blue = blue
green = green
red = red

And now you can see why Python doesn't support this idiom.

Maybe it would make more sense if it was done a la Visual Basic

with self:
.blue = blue
.green = green
.red = red

requiring a dot to be typed removes the ambiguity and gives the IDEs a
chance to Intellisense-ify your coding.

Some made a python recipe emulating this I believe. The python cookbook
search engine is down though so I cannot find the link.
At one point Guido van Rossum was advocating this use of "with" as well,
I believe:
http://mail.python.org/pipermail/pyt...ch/043545.html

But I don't think it is being considered now. I think now "with" is
being proposed for something more like VB and C#'s "using" statement.
It automatically disposes of a resource when done with it:
http://wiki.python.org/moin/WithStatement

[Sergei Organov]

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:

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

.... and now you need to check the declarations of C, B, and A to
actually see what is assigned to what.

Worse yet, adding field 'x' to 'C' will (silently) break the code :(

I don't think it would be that nice to have it in Python.

--
Sergei.

[Tom Anderson]

On Fri, 24 Jun 2005, Joseph Garvin wrote:

Claudio Grondi wrote:

So far we've got lisp macros and a thousand response's to the lua trick.
Anyone else have any actual non-python language tricks they like?

Higher-order functions like map, filter and reduce. As of Python 3000,
they're non-python tricks. Sigh - i guess it's time for me to get to know
list comprehensions a bit better.

The one thing i really do miss is method overloading by parameter type. I
used this all the time in java, and it really notice the lack of it
sometimes in python. No, it's not really possible in a typeless language,
and yes, there are implementations based on decorators, but frankly,
they're awful.

Yeah, and i'm with "if False:" for commenting out chunks of code.

tom

--
.... but when you spin it it looks like a dancing foetus!