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Method default argument whose type is the class not yet defined

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  Method default argument whose type is the class not yet defined Jennie <nameDOTportua@gmail.com> - 2012-11-10 20:33 +0100
    Re: Method default argument whose type is the class not yet defined Chris Angelico <rosuav@gmail.com> - 2012-11-11 06:56 +1100
    Re: Method default argument whose type is the class not yet defined Terry Reedy <tjreedy@udel.edu> - 2012-11-10 15:29 -0500
      Re: Method default argument whose type is the class not yet defined Jennie <nameDOTportua@gmail.com> - 2012-11-10 21:51 +0100
        Re: Method default argument whose type is the class not yet defined Dave Angel <d@davea.name> - 2012-11-10 17:30 -0500
      Re: Method default argument whose type is the class not yet defined Jennie <marco.buttu@gmail.com> - 2012-11-10 21:51 +0100
    Re: Method default argument whose type is the class not yet defined Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-11 01:13 +0000
      Re: Method default argument whose type is the class not yet defined Chris Angelico <rosuav@gmail.com> - 2012-11-11 13:13 +1100
      Re: Method default argument whose type is the class not yet defined Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-10 19:43 -0700
        Re: Method default argument whose type is the class not yet defined Roy Smith <roy@panix.com> - 2012-11-10 21:53 -0500
          Re: Method default argument whose type is the class not yet defined Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-10 23:43 -0700
          Re: Method default argument whose type is the class not yet defined Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-10 23:45 -0700
      Re: Method default argument whose type is the class not yet defined Chris Angelico <rosuav@gmail.com> - 2012-11-11 13:47 +1100
      Re: Method default argument whose type is the class not yet defined Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-11 14:21 +0000
        Re: Method default argument whose type is the class not yet defined Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-11 22:31 +0000
          Re: Method default argument whose type is the class not yet defined Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-12 00:31 +0000
            Re: Method default argument whose type is the class not yet defined Steve Howell <showell30@yahoo.com> - 2012-11-11 16:56 -0800
            Re: Method default argument whose type is the class not yet defined Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-12 04:46 +0000
          Re: Method default argument whose type is the class not yet defined Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-11-12 01:10 +0000
            Re: Method default argument whose type is the class not yet defined Roy Smith <roy@panix.com> - 2012-11-11 20:15 -0500
              Re: Method default argument whose type is the class not yet defined Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-11-12 01:35 +0000
          Re: Method default argument whose type is the class not yet defined Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-12 01:18 +0000
            Re: Method default argument whose type is the class not yet defined Roy Smith <roy@panix.com> - 2012-11-11 20:34 -0500
          Re: Method default argument whose type is the class not yet defined Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-11-12 01:29 +0000
          Re: Method default argument whose type is the class not yet defined Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-12 01:50 +0000
    Re: Method default argument whose type is the class not yet defined Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-11 01:23 +0000
    Re: Method default argument whose type is the class not yet defined Steve Howell <showell30@yahoo.com> - 2012-11-11 16:32 -0800

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#33163

On 12/11/2012 01:15, Roy Smith wrote:
> In article <mailman.3570.1352682390.27098.python-list@python.org>,
>   Mark Lawrence <breamoreboy@yahoo.co.uk> wrote:
>
>> On 12/11/2012 00:31, Oscar Benjamin wrote:
>>>
>>> Plain wrong. Vectors are not defined *from any origin*.
>>>
>>
>> So when the Captain says "full speed ahead, steer 245 degrees", you
>> haven't the faintest idea where you're going, because you have no origin?
>
> Vectors have a length ("full speed ahead") and a direction ("245
> degrees").  What they don't have is a fixed location in space.  The
> captain didn't say, "Full speed ahead, steer 245 degrees, from 45.0N,
> 20.0W".
>
> In other words, you are correct.  The order, "full speed ahead, steer
> 245 degrees", doesn't give you the faintest idea of where you're going.
> If you were the helmsman, after you executed that order, without any
> additional information (such as your current location), you would have
> no idea what piece of land you will hit, or when you will hit it, if you
> maintain your current course and speed.
>

Thank you for your explanation.

-- 
Cheers.

Mark Lawrence.

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#33160

On 12 November 2012 01:10, Mark Lawrence <breamoreboy@yahoo.co.uk> wrote:
> On 12/11/2012 00:31, Oscar Benjamin wrote:
>>
>>
>> Plain wrong. Vectors are not defined *from any origin*.
>>
>
> So when the Captain says "full speed ahead, steer 245 degrees", you haven't
> the faintest idea where you're going, because you have no origin?

As Steve has just explained, the origin has nothing to do with the
orientation of the coordinate system.

But then I'm assuming you meant that 245 degrees was a bearing
relative to North. Was it supposed to be relative to my current angle?
Truthfully I wouldn't know what to do without asking the captain a
couple more questions.


Oscar

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#33162

In article <mailman.3571.1352683098.27098.python-list@python.org>,
 Oscar Benjamin <oscar.j.benjamin@gmail.com> wrote:

> But then I'm assuming you meant that 245 degrees was a bearing
> relative to North. Was it supposed to be relative to my current angle?
> Truthfully I wouldn't know what to do without asking the captain a
> couple more questions.

Granted, this requires some domain-specific knowledge, but an order to 
"steer 245 degrees" means relative to north (and, technically, it's a 
heading, not a bearing, but that's another discussion).

If the captain wanted you to change you heading relative to your current 
heading, he would say something like, "turn left 10 degrees" (that may 
not be strictly the correct wording).

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#33161

On 12/11/2012 01:18, Oscar Benjamin wrote:
> On 12 November 2012 01:10, Mark Lawrence <breamoreboy@yahoo.co.uk> wrote:
>> On 12/11/2012 00:31, Oscar Benjamin wrote:
>>>
>>>
>>> Plain wrong. Vectors are not defined *from any origin*.
>>>
>>
>> So when the Captain says "full speed ahead, steer 245 degrees", you haven't
>> the faintest idea where you're going, because you have no origin?
>
> As Steve has just explained, the origin has nothing to do with the
> orientation of the coordinate system.
>
> But then I'm assuming you meant that 245 degrees was a bearing
> relative to North. Was it supposed to be relative to my current angle?
> Truthfully I wouldn't know what to do without asking the captain a
> couple more questions.
>
>
> Oscar
>

The only good acedemic is a dead acedemic?

-- 
Cheers.

Mark Lawrence.

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#33165

On 12 November 2012 01:29, Mark Lawrence <breamoreboy@yahoo.co.uk> wrote:
> On 12/11/2012 01:18, Oscar Benjamin wrote:
>>
>> On 12 November 2012 01:10, Mark Lawrence <breamoreboy@yahoo.co.uk> wrote:
>>>
>>> On 12/11/2012 00:31, Oscar Benjamin wrote:
>>>>
>>>> Plain wrong. Vectors are not defined *from any origin*.
>>>
>>> So when the Captain says "full speed ahead, steer 245 degrees", you
>>> haven't
>>> the faintest idea where you're going, because you have no origin?
>>
>>
>> As Steve has just explained, the origin has nothing to do with the
>> orientation of the coordinate system.
>>
>> But then I'm assuming you meant that 245 degrees was a bearing
>> relative to North. Was it supposed to be relative to my current angle?
>> Truthfully I wouldn't know what to do without asking the captain a
>> couple more questions.
>
> The only good acedemic is a dead acedemic?

Is that what happens when people ask questions on your ship: "it's the
plank for him with the questions-askin'!"

I'm glad you're not my captain.


Oscar

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#33111

On 10 November 2012 19:33, Jennie <nameDOTportua@gmail.com> wrote:
> What is the best solution to solve the following problem in Python 3.3?
>
> import math
>>>> class Point:
> ...     def __init__(self, x=0, y=0):
> ...         self.x = x
> ...         self.y = y
> ...     def __sub__(self, other):
> ...         return Point(self.x - other.x, self.y - other.y)
> ...     def distance(self, point=Point()):
> ...         """Return the distance from `point`."""
> ...         return math.sqrt((self - point).x ** 2 + (self - point).y ** 2)
> ...
> Traceback (most recent call last):
>   File "<stdin>", line 1, in <module>
>   File "<stdin>", line 5, in Point
> NameError: name 'Point' is not defined

I would use namedtuple and make it so that an ordinary tuple could be
used as in place of a Point instance:

>>> import math
>>> from collections import namedtuple
>>> class Point(namedtuple('Point', ['x', 'y'])):
...   def distance(self, other=(0, 0)):
...     (myx, myy), (theirx, theiry) = self, other
...     return math.sqrt((myx - theirx) ** 2 + (myy - theiry) ** 2)
...
>>> p = Point(3, 4)
>>> p.distance()
5.0
>>> p2 = Point(4, 5)
>>> p.distance(p2)
1.4142135623730951


Oscar

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#33155

On Nov 10, 11:33 am, Jennie <nameDOTpor...@gmail.com> wrote:
> What is the best solution to solve the following problem in Python 3.3?
>
> import math
>  >>> class Point:
> ...     def __init__(self, x=0, y=0):
> ...         self.x = x
> ...         self.y = y
> ...     def __sub__(self, other):
> ...         return Point(self.x - other.x, self.y - other.y)
> ...     def distance(self, point=Point()):
> ...         """Return the distance from `point`."""
> ...         return math.sqrt((self - point).x ** 2 + (self - point).y ** 2)

Before you do anything else, introduce a Vector class into your app.
The difference between two Points is not a Point; it's a Vector.
Create a magnitude() method in your Vector class, then make your
Point.distance return the results of Vector.magnitude(self - other).
To define the distance of a point from the origin, don't make your
distance() method have default arguments; instead, define another
method called distance_from_origin().

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