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increment/decrement operators

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  increment/decrement operators Tony van der Hoff <tony@vanderhoff.org> - 2015-12-05 12:40 +0000
    Re: increment/decrement operators Robin Koch <robin.koch@t-online.de> - 2015-12-05 13:56 +0100
      Re: increment/decrement operators Tony van der Hoff <tony@vanderhoff.org> - 2015-12-05 14:14 +0000
      Re: increment/decrement operators "D'Arcy J.M. Cain" <darcy@VybeNetworks.com> - 2015-12-05 09:41 -0500
      Re: increment/decrement operators Terry Reedy <tjreedy@udel.edu> - 2015-12-05 10:43 -0500
        Re: increment/decrement operators BartC <bc@freeuk.com> - 2015-12-05 17:18 +0000
          Re: increment/decrement operators Ian Kelly <ian.g.kelly@gmail.com> - 2015-12-07 17:24 -0700

#100035 — increment/decrement operators

Hi,

I'm a relative newbie to python, and this NG, but it's certainly growing 
on me.

One thing I'm missing is the increment/decrement operator from C, ie 
x++, and its ilk. Likewise x += y.

is there any way of doing this in Python?

TIA, Tony

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#100036

Am 05.12.2015 um 13:40 schrieb Tony van der Hoff:
> Hi,
>
> I'm a relative newbie to python, and this NG, but it's certainly growing
> on me.
>
> One thing I'm missing is the increment/decrement operator from C, ie
> x++, and its ilk. Likewise x += y.
>
> is there any way of doing this in Python?

Quick answer:

x += y works. (Well, it should.)

x++ doesn't.

Long answer:

I'm sure someone more experienced will come up with one shortly. :-)

Until then I found this:
http://stackoverflow.com/a/1485854

-- 
Robin Koch

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#100038

On 05/12/15 12:56, Robin Koch wrote:
> Am 05.12.2015 um 13:40 schrieb Tony van der Hoff:
>> Hi,
>>
>> I'm a relative newbie to python, and this NG, but it's certainly growing
>> on me.
>>
>> One thing I'm missing is the increment/decrement operator from C, ie
>> x++, and its ilk. Likewise x += y.
>>
>> is there any way of doing this in Python?
>
> Quick answer:
>
> x += y works. (Well, it should.)
>
> x++ doesn't.
>
> Long answer:
>
> I'm sure someone more experienced will come up with one shortly. :-)
>
> Until then I found this:
> http://stackoverflow.com/a/1485854
>
Thanks for the link

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#100039

On Sat, 5 Dec 2015 13:56:47 +0100
Robin Koch <robin.koch@t-online.de> wrote:
> x += y works. (Well, it should.)

It does, even on objects other than numbers.

>>> x = "abc"
>>> y = "def"
>>> x += y
>>> x
'abcdef'

> x++ doesn't.

No but it's just a special case of the above.

>>> x = 1
>>> x += 1
>>> x
2

-- 
D'Arcy J.M. Cain
Vybe Networks Inc.
http://www.VybeNetworks.com/
IM:darcy@Vex.Net VoIP: sip:darcy@VybeNetworks.com

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#100040

On 12/5/2015 9:41 AM, D'Arcy J.M. Cain wrote:
> On Sat, 5 Dec 2015 13:56:47 +0100
> Robin Koch <robin.koch@t-online.de> wrote:
>> x += y works. (Well, it should.)
>
> It does, even on objects other than numbers.
>
>>>> x = "abc"
>>>> y = "def"
>>>> x += y
>>>> x
> 'abcdef'
>
>> x++ doesn't.
>
> No but it's just a special case of the above.
>
>>>> x = 1
>>>> x += 1
>>>> x
> 2

Apple is removing the ++ and -- pre- and post- increment and decrement 
operators from Swift 3.0 as redundant with += 1.
https://github.com/apple/swift-evolution/blob/master/proposals/0004-remove-pre-post-inc-decrement.md

The following section is a good summary of why they were never added to 
Python, and should not be.

'''
Disadvantages of These Operators

1. These operators increase the burden to learn Swift as a first 
programming language - or any other case where you don't already know 
these operators from a different language.

2. Their expressive advantage is minimal - x++ is not much shorter than 
x += 1.

3. Swift already deviates from C in that the =, += and other 
assignment-like operations returns Void (for a number of reasons). These 
operators are inconsistent with that model.

4. Swift has powerful features that eliminate many of the common reasons 
you'd use ++i in a C-style for loop in other languages, so these are 
relatively infrequently used in well-written Swift code. These features 
include the for-in loop, ranges, enumerate, map, etc.

5. Code that actually uses the result value of these operators is often 
confusing and subtle to a reader/maintainer of code. They encourage 
"overly tricky" code which may be cute, but difficult to understand.

6. While Swift has well defined order of evaluation, any code that 
depended on it (like foo(++a, a++)) would be undesirable even if it was 
well-defined.

7. These operators are applicable to relatively few types: integer and 
floating point scalars, and iterator-like concepts. They do not apply to 
complex numbers, matrices, etc.

8. Having to support these could add complexity to the potential revised 
numerics model.

Finally, these fail the metric of "if we didn't already have these, 
would we add them to Swift 3?"
'''

-- 
Terry Jan Reedy

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#100041

On 05/12/2015 15:43, Terry Reedy wrote:
> On 12/5/2015 9:41 AM, D'Arcy J.M. Cain wrote:
>> On Sat, 5 Dec 2015 13:56:47 +0100
>> Robin Koch <robin.koch@t-online.de> wrote:
>>> x += y works. (Well, it should.)
>>
>> It does, even on objects other than numbers.
>>
>>>>> x = "abc"
>>>>> y = "def"
>>>>> x += y
>>>>> x
>> 'abcdef'
>>
>>> x++ doesn't.
>>
>> No but it's just a special case of the above.
>>
>>>>> x = 1
>>>>> x += 1
>>>>> x
>> 2
>
> Apple is removing the ++ and -- pre- and post- increment and decrement
> operators from Swift 3.0 as redundant with += 1.
> https://github.com/apple/swift-evolution/blob/master/proposals/0004-remove-pre-post-inc-decrement.md
>
>
> The following section is a good summary of why they were never added to
> Python, and should not be.
>
> '''
> Disadvantages of These Operators
>
> 1. These operators increase the burden to learn Swift as a first
> programming language - or any other case where you don't already know
> these operators from a different language.
>
> 2. Their expressive advantage is minimal - x++ is not much shorter than
> x += 1.

The latter is not the same. Some of the differences are:

* ++ and -- are often inside inside expressions and return values 
(unlike x+=1 in Python)

* x++ and x-- return the /current/ value of x, unlike x+=1 even if it 
were to return a value; it would be the new value

* x+=1 requires you to hard-code the value 1, but ++ is not necessarily 
stepping by 1. You can imagine ++ stepping something to its next value.

However, if ++ and -- are only used as statements, then why not simply 
map them to x+=1? In Python, that would need to be x++ and x-- as ++x or 
--x have existing meanings.

-- 
Bartc

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#100121

On Dec 5, 2015 10:21 AM, "BartC" <bc@freeuk.com> wrote:

>

>

> The latter is not the same. Some of the differences are:

>

> * ++ and -- are often inside inside expressions and return values (unlike
x+=1 in Python)

>

> * x++ and x-- return the /current/ value of x, unlike x+=1 even if it
were to return a value; it would be the new value

Since x+=1 is not an expression, this is moot.

> * x+=1 requires you to hard-code the value 1, but ++ is not necessarily
stepping by 1. You can imagine ++ stepping something to its next value.

Note that x+=1 does not necessarily have to mean stepping by 1 either. You
could even do something like x+=5 to mean skip the next four values and
step x to the value after that.

> However, if ++ and -- are only used as statements, then why not simply
map them to x+=1? In Python, that would need to be x++ and x-- as ++x or
--x have existing meanings.

I think a better question is if they're only going to be statements, then
why bother adding them? x++ doesn't give you anything you can't get from
x+=1, so why commit to supporting the extra syntax?

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