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| From | Thomas 'PointedEars' Lahn <PointedEars@web.de> |
| Newsgroups | comp.lang.python |
| Subject | Re: Question about math.pi is mutable |
| Date | Fri, 06 Nov 2015 23:19:42 +0100 |
| Organization | PointedEars Software (PES) |
| Lines | 51 |
| Message-ID | <1521937.lCYGF7V2BE@PointedEars.de> (permalink) |
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Chris Angelico wrote:
> On Sat, Nov 7, 2015 at 6:30 AM, Bartc <bc@freeuk.com> wrote:
>> Is there no way then in Python to declare:
>>
>> pi = 3.141519 # etc
>>
>> and make it impossible to override?
>
> Nope. Even in C++, where classes can define certain things as const,
> private, and other such restrictions, you can always get around them
> by manipulating pointers appropriately. In Python, there's a
> *convention* that a leading underscore means "private", but the
> language doesn't enforce anything about it.
It is certainly possible for attributes of (instances of) new-style classes
(starting with Python 3.2 at the latest) to be read-only by declaring them a
property that does not have a setter, or one that has a setter that throws a
specific exception (here: the former):
#--------------------------
class SafeMath(object):
def __init__ (self):
from math import pi
self._pi = pi
@property
def pi (self):
return self._pi
#--------------------------
| >>> math = SafeMath()
| >>> math.pi
| 3.141592653589793
| >>> math.pi = 42
| Traceback (most recent call last):
| File "<stdin>", line 1, in <module>
| AttributeError: can't set attribute
(Or you can use “pi = property(…)” within the class declaration.)
In theory, it should be possible to substitute “math” with a reference to an
object that acts as a proxy for the original “math” module object but whose
base class declares the attributes for all the constants read-only.
--
PointedEars
Twitter: @PointedEars2
Please do not cc me. / Bitte keine Kopien per E-Mail.
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Question about math.pi is mutable "wangq@travelsky.com" <wangq@travelsky.com> - 2015-11-06 10:33 +0800
Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-06 12:30 +0000
Re: Question about math.pi is mutable Lorenzo Sutton <lorenzofsutton@gmail.com> - 2015-11-06 17:12 +0100
Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-06 19:30 +0000
Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-07 06:40 +1100
Re: Question about math.pi is mutable Christian Gollwitzer <auriocus@gmx.de> - 2015-11-06 20:59 +0100
Re: Question about math.pi is mutable Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-11-06 23:19 +0100
Re: Question about math.pi is mutable Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-11-07 00:48 +0100
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-07 13:00 +1100
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-07 14:43 +1100
Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 11:23 +0000
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-07 22:35 +1100
Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 11:57 +0000
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-07 23:15 +1100
Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 13:00 +0000
Re: Question about math.pi is mutable Laura Creighton <lac@openend.se> - 2015-11-07 15:09 +0100
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-07 16:23 +0200
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Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-07 19:46 +0200
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-08 14:07 +1100
Re: Question about math.pi is mutable Random832 <random832@fastmail.com> - 2015-11-08 01:29 -0500
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-08 13:59 +1100
Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-08 10:40 +0000
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 13:02 +0200
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 11:19 +0000
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 13:50 +0200
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 12:39 +0000
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 14:43 +0200
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 13:42 +0000
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 16:33 +0200
Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 02:11 +1100
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-09 11:58 +1100
Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-08 23:28 +1100
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Re: Question about math.pi is mutable Michael Torrie <torriem@gmail.com> - 2015-11-08 08:59 -0700
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 17:54 +0000
Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 05:01 +1100
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 18:58 +0000
Re: Question about math.pi is mutable Ian Kelly <ian.g.kelly@gmail.com> - 2015-11-08 12:51 -0700
Re: Question about math.pi is mutable Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-11-08 18:13 -0500
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 23:54 +0000
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 11:00 +1100
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-09 00:11 +0000
Re: Question about math.pi is mutable Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2015-11-09 08:18 -0500
Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 11:04 +1100
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 11:26 +1100
Re: Question about math.pi is mutable Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2015-11-09 21:29 +1300
Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 11:36 +1100
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 11:50 +1100
Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 11:56 +1100
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 12:04 +1100
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-09 22:22 +1100
Re: Question about math.pi is mutable Random832 <random832@fastmail.com> - 2015-11-09 10:32 -0500
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 06:45 +1100
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-10 13:37 +1100
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 17:10 +1100
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-10 22:34 +1100
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-10 13:26 +0000
Re: Question about math.pi is mutable Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-11-11 18:38 +1100
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-11 10:30 +0200
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Re: Question about math.pi is mutable Terry Reedy <tjreedy@udel.edu> - 2015-11-10 03:30 -0500
Re: Question about math.pi is mutable Laura Creighton <lac@openend.se> - 2015-11-10 11:33 +0100
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 23:14 +1100
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Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 06:52 +1100
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 08:00 +1100
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 22:35 +0000
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-09 09:54 +1100
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-09 13:23 +1100
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-09 12:22 +0000
Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-09 23:36 +1100
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-08 22:30 +1100
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 12:24 +0000
Re: Question about math.pi is mutable Grant Edwards <invalid@invalid.invalid> - 2015-11-07 16:16 +0000
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-07 20:00 +0200
Re: Question about math.pi is mutable Grant Edwards <invalid@invalid.invalid> - 2015-11-08 03:31 +0000
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 09:45 +0200
Re: Question about math.pi is mutable Christian Gollwitzer <auriocus@gmx.de> - 2015-11-08 09:00 +0100
Re: Question about math.pi is mutable Paul Rubin <no.email@nospam.invalid> - 2015-11-08 00:08 -0800
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 11:49 +0200
Re: Question about math.pi is mutable Grant Edwards <invalid@invalid.invalid> - 2015-11-09 14:49 +0000
Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 15:19 +0000
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-08 14:50 +1100
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 11:44 +0200
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-08 22:11 +1100
Re: Question about math.pi is mutable Marko Rauhamaa <marko@pacujo.net> - 2015-11-08 13:25 +0200
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-08 11:06 +0000
Re: Question about math.pi is mutable Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-09 15:49 +0100
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-10 10:29 +1100
Re: Question about math.pi is mutable Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-10 11:03 +0100
Re: Question about math.pi is mutable Michael Torrie <torriem@gmail.com> - 2015-11-13 20:11 -0700
Re: Question about math.pi is mutable Antoon Pardon <antoon.pardon@rece.vub.ac.be> - 2015-11-14 16:02 +0100
Re: Question about math.pi is mutable Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-11-06 23:26 +0100
Re: Question about math.pi is mutable Terry Reedy <tjreedy@udel.edu> - 2015-11-06 20:49 -0500
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-07 13:06 +1100
Re: Question about math.pi is mutable Bartc <bc@freeuk.com> - 2015-11-07 23:02 +0000
Re: Question about math.pi is mutable Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-11-07 23:27 +0000
Re: Question about math.pi is mutable Ben Finney <ben+python@benfinney.id.au> - 2015-11-08 10:32 +1100
Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-08 10:52 +1100
Re: Question about math.pi is mutable Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2015-11-12 21:40 +0100
Re: Question about math.pi is mutable Steven D'Aprano <steve@pearwood.info> - 2015-11-13 09:04 +1100
Re: Question about math.pi is mutable Denis McMahon <denismfmcmahon@gmail.com> - 2015-11-13 09:19 +0000
Re: Question about math.pi is mutable Larry Hudson <orgnut@yahoo.com> - 2015-11-13 18:30 -0800
Re: Question about math.pi is mutable BartC <bc@freeuk.com> - 2015-11-12 22:19 +0000
Re: Question about math.pi is mutable Chris Angelico <rosuav@gmail.com> - 2015-11-13 09:52 +1100
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