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Re: Python ++ Operator?

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  Re: Python ++ Operator? Chris Angelico <rosuav@gmail.com> - 2011-07-15 18:06 +1000
    Re: Python ++ Operator? Chris Torek <nospam@torek.net> - 2011-07-19 19:08 +0000

#9525 — Re: Python ++ Operator?

2011/7/15 Björn Lindqvist <bjourne@gmail.com>:
> Pre and post-increments are
> almost always confusing unless they are used as the counter-variable
> inside for-loops.

I agree that they're often confusing (i+++++j) but there are several
places where they're handy.

array[count++]=value;

or the more direct pointer management:

*ptr++=value;

However, Python doesn't work as close to the bare metal, so it doesn't
have such constructs.

ChrisA

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#9915

In article <mailman.1057.1310717193.1164.python-list@python.org>
Chris Angelico  <rosuav@gmail.com> wrote:
>I agree that [C's ++ operators are] often confusing (i+++++j) ...

For what it is worth, this has to be written as:

    i++ + ++j /* or i+++ ++j */

or similar (e.g., newline after the middle "+" operator) as the
lexer will group adjacent "++" characters into a single "++" operator
whenever it can (the so-called "greedy matching" that regular
expression recognizers are famous for), and only later will the
parser and semantic analysis phases realize that "i++ ++ +j" is
invalid and complain.

>but there are several places where they're handy. ...
>However, Python doesn't work as close to the bare metal, so it
>doesn't have such constructs.

More specifically, Python has appropriate higher-level constructs
that, in effect, maintain "mental invariants" in a better (for some
value of better) way.  Instead of:

    lst[i++] = val; /* or: *p++ = val; */

which has the effect of appending an item to an array-based list
of items -- the "invariant" here is that i (or p in the pointer
version) always tells you where the place the *next* item -- one
simply writes:

    lst.append(val)

(which also makes sure that there is *room* in the array-based
list, something that requires a separate step in C).
-- 
In-Real-Life: Chris Torek, Wind River Systems
Intel require I note that my opinions are not those of WRS or Intel
Salt Lake City, UT, USA (40°39.22'N, 111°50.29'W)  +1 801 277 2603
email: gmail (figure it out)      http://web.torek.net/torek/index.html

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