On 2 January 2013 17:59, Alan Gauld wrote:
> On 01/02/2013 11:41 AM, Steven D'Aprano wrote:
>
>[SNIP]
>> But __index__ is a special method that converts to int without rounding
>> or truncating, intended only for types that emulate ints but not other
>> numeric types:
>
>
> And this was the new bi
On Tue, Jan 1, 2013 at 12:07 AM, Steven D'Aprano wrote:
>
> Again, I was mistaken. x%1 is not suitable to get the fraction part of a
> number in Python: it returns the wrong result for negative values. You need
> math.modf:
>
> py> x = -99.25
> py> x % 1 # want -0.25
> 0.75
> py> math.modf(x)
> (
On 02/01/13 16:55, Dave Angel wrote:
On 01/02/2013 11:41 AM, Steven D'Aprano wrote:
The bit about __index__ refers to using trunc():
OK, that partially solves it :-)
I don't know what this "index() builtin" is, it doesn't appear to exist.
That was also what confused me. The only indexz(
On 01/02/2013 11:41 AM, Steven D'Aprano wrote:
>
>
> The bit about __index__ refers to using trunc():
>
> "I still really wish I had followed Pascal's lead instead of C's here:
> Pascal requires you to use trunc() to convert a real to an integer. ...
> If we had done it that way, we wouldn't have
On 03/01/13 03:18, Alan Gauld wrote:
This is going somewhat off-topic but my curiosity is roused...
On 02/01/13 15:16, Oscar Benjamin wrote:
When the idea was discussed in the run up to Python 3, Guido raised
exactly this case and said
"""...
(BTW Pascal also had the division operator right, u
This is going somewhat off-topic but my curiosity is roused...
On 02/01/13 15:16, Oscar Benjamin wrote:
> When the idea was discussed in the run up to Python 3, Guido raised
exactly this case and said
"""...
(BTW Pascal also had the division operator right, unlike C, and we're
... If we had do
On 1 January 2013 05:07, Steven D'Aprano wrote:
> On 23/12/12 04:38, Oscar Benjamin wrote:
>>
>> On 22 December 2012 01:34, Steven D'Aprano wrote:
>>>
>>> On 18/12/12 01:36, Oscar Benjamin wrote:
>>>
I think it's unfortunate that Python's int() function combines two
distinct behaviours
On 23/12/12 04:38, Oscar Benjamin wrote:
On 22 December 2012 01:34, Steven D'Aprano wrote:
On 18/12/12 01:36, Oscar Benjamin wrote:
I think it's unfortunate that Python's int() function combines two
distinct behaviours in this way. In different situations int() is used
to:
1) Coerce an object
On Thu, Dec 27, 2012 at 12:13 PM, Oscar Benjamin
wrote:
>
> I hadn't realised that. Does the int(obj) function use isinstance(obj,
> str) under the hood?
Yes. int_new and long_new use the macros PyString_Check (in 3.x
PyBytes_Check) and PyUnicode_Check, which check the type's tp_flags.
The C API
On 27 December 2012 17:49, Steven D'Aprano wrote:
> On 23/12/12 04:57, Oscar Benjamin wrote:
>>
>> On 22 December 2012 02:06, Steven D'Aprano wrote:
>>>
>>> On 18/12/12 01:36, Oscar Benjamin wrote:
>>>
I have often found myself writing awkward functions to prevent a
rounding error from
On 23/12/12 04:57, Oscar Benjamin wrote:
On 22 December 2012 02:06, Steven D'Aprano wrote:
On 18/12/12 01:36, Oscar Benjamin wrote:
I have often found myself writing awkward functions to prevent a
rounding error from occurring when coercing an object with int().
Here's one:
def make_int(obj)
On 24 December 2012 04:42, eryksun wrote:
> On Sat, Dec 22, 2012 at 12:57 PM, Oscar Benjamin
> wrote:
def make_int(obj):
'''Coerce str, float and int to int without rounding error
Accepts strings like '4.0' but not '4.1'
'''
fnum = float('%s' % ob
On Sat, Dec 22, 2012 at 12:57 PM, Oscar Benjamin
wrote:
>>>
>>> def make_int(obj):
>>> '''Coerce str, float and int to int without rounding error
>>> Accepts strings like '4.0' but not '4.1'
>>> '''
>>> fnum = float('%s' % obj)
>>> inum = int(fnum)
>>> assert inum ==
On 22 December 2012 01:34, Steven D'Aprano wrote:
> On 18/12/12 01:36, Oscar Benjamin wrote:
>
>> I think it's unfortunate that Python's int() function combines two
>> distinct behaviours in this way. In different situations int() is used
>> to:
>> 1) Coerce an object of some type other than int i
Oh, another comment...
On 18/12/12 01:36, Oscar Benjamin wrote:
I have often found myself writing awkward functions to prevent a
rounding error from occurring when coercing an object with int().
Here's one:
def make_int(obj):
'''Coerce str, float and int to int without rounding error
On 18/12/12 01:36, Oscar Benjamin wrote:
I think it's unfortunate that Python's int() function combines two
distinct behaviours in this way. In different situations int() is used
to:
1) Coerce an object of some type other than int into an int without
changing the value of the integer that the ob
On Mon, Dec 17, 2012 at 1:00 PM, Alan Gauld wrote:
>
> Python uses its own C code for this.
The important point here is that they use the strtol/strtod interface,
however it's implemented. atoi and atof lack the end pointer argument
that enables raising a ValueError for an incomplete conversion.
On 17/12/12 14:36, Oscar Benjamin wrote:
> Even stranger since the underlying atoi() C function
Also, are you sure that atoi() is used in CPython?
Nope, just making assumptions! :-0
As Eryksun points out Python uses its own C code for this.
assume == ass u me :-(
--
Alan G
Author of the
On Mon, Dec 17, 2012 at 3:55 AM, Alan Gauld wrote:
>
> So you are right, there is an inconsistency between how int() converts
> floating point numbers and how it converts strings. Even stranger since the
> underlying atoi() C function appears to handle float strings quite
> happily...
If you're u
On 17 December 2012 08:55, Alan Gauld wrote:
>
> On 17/12/12 04:19, boB Stepp wrote:
>
>> It is apparent that int() does not like strings with floating-point
>> formats. None of my books (as far as my flipping can tell) or the
>> below built-in help clarify this:
>> ...
>>
>> Of course if I type i
On 17/12/12 04:19, boB Stepp wrote:
It is apparent that int() does not like strings with floating-point
formats. None of my books (as far as my flipping can tell) or the
below built-in help clarify this:
...
Of course if I type int(float('10.0')) I get the desired 10 .
as indeed will
int(10.0
On 12/17/2012 12:00 AM, boB Stepp wrote:
On Sun, Dec 16, 2012 at 10:41 PM, Mitya Sirenef wrote:
>
>> What would you want to happen for int("10.5")? If 10.0 was accepted,
>> it would be consistent to accept 10.5, too.
>
> I was expecting int("10.5") to return 10 .
I just want to note that thi
On Sun, Dec 16, 2012 at 10:41 PM, Mitya Sirenef wrote:
> What would you want to happen for int("10.5")? If 10.0 was accepted,
> it would be consistent to accept 10.5, too.
I was expecting int("10.5") to return 10 .
> The issue, I think, is that a simple operation should not go too far
> beyond
On 12/16/2012 11:19 PM, boB Stepp wrote:
int('10.0')
> Traceback (most recent call last):
> File "", line 1, in
> ValueError: invalid literal for int() with base 10: '10.0'
int("10")
> 10
>
> It is apparent that int() does not like strings with floating-point
> formats. None of my books (a
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