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Re: Code style query: multiple assignments in if/elif tree

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On Mon, Mar 31, 2014 at 11:45 PM, Rustom Mody <rustompmody@gmail.com> wrote:
> On Tue, Apr 1, 2014 at 3:26 PM, Steven D'Aprano  wrote:
>
>> Haskell has nifty pattern-matching syntax for this that looks quite close
>> to the mathematical hybrid function syntax, but in Python, we're limited
>> to explicitly using an if. If I were coding this, and I'm not, I'd wrap
>> it in a function. One advantage of a state variable rather than a
>> continuous time function is that we can do this:
>> def accel(state):
>>     return {NO_BRAKING: 0.0,
>>             LOW_BRAKING: 0.2,
>>             MID_BRAKING: 0.425,
>>             HIGH_BRAKING: 0.85}[state]
>
> Neat
> I would put the dict in a variable. And those _BRAKINGs are GALLing me!
>
> breaking = {NO:0.0, LOW:0.2, MID:0.425:, HIGH:0.85}
> def accel(state): return breaking[state]

If I were doing this in Python 3.4 I would be sorely tempted to use an
Enum for the state.  Then the acceleration could just be an attribute
(or method) of the state itself!

class BrakingState(Enum):
    no_braking = 0.0
    low_braking = 0.2
    mid_braking = 0.425
    high_braking = 0.85

    @property
    def acceleration(self):
        return self.value

>>> print(BrakingState.low_braking.acceleration)
0.2


Alternatively the __init__ method could set the acceleration directly
from the value(s) passed in, as in the Planet example:

https://docs.python.org/3/library/enum.html#planet

The problem I have with either of these approaches though is that if
two distinct states happen to have the same acceleration, they will be
considered aliases for the same state.  This is because the
acceleration value is doing double duty as a parameter of the state
and also as its identity.  Likewise in the Planet example, if a new
planet happened to have the same mass and radius as Jupiter, it would
be considered the same planet as Jupiter. I haven't managed to work
out a wholly satisfying way to avoid this.

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Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 01:33 +1100
  Re: Code style query: multiple assignments in if/elif tree Marko Rauhamaa <marko@pacujo.net> - 2014-03-31 18:40 +0300
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 03:03 +1100
      Re: Code style query: multiple assignments in if/elif tree Rustom Mody <rustompmody@gmail.com> - 2014-03-31 09:20 -0700
        Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 03:29 +1100
          Re: Code style query: multiple assignments in if/elif tree "Rhodri James" <rhodri@wildebst.org.uk> - 2014-03-31 21:31 +0100
    Re: Code style query: multiple assignments in if/elif tree Ned Batchelder <ned@nedbatchelder.com> - 2014-03-31 17:42 -0400
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 09:50 +1100
    Re: Code style query: multiple assignments in if/elif tree Ben Finney <ben+python@benfinney.id.au> - 2014-04-01 09:57 +1100
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 10:12 +1100
      Re: Code style query: multiple assignments in if/elif tree Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-04-01 00:57 +0000
    Re: Code style query: multiple assignments in if/elif tree Ethan Furman <ethan@stoneleaf.us> - 2014-03-31 17:30 -0700
  Re: Code style query: multiple assignments in if/elif tree Steven D'Aprano <steve@pearwood.info> - 2014-04-01 04:26 +0000
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 16:01 +1100
      Re: Code style query: multiple assignments in if/elif tree Steven D'Aprano <steve@pearwood.info> - 2014-04-01 07:20 +0000
        Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 18:35 +1100
          Re: Code style query: multiple assignments in if/elif tree Steven D'Aprano <steve@pearwood.info> - 2014-04-01 08:07 +0000
            Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 19:12 +1100
        Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 02:18 -0600
        Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 02:24 -0600
    Re: Code style query: multiple assignments in if/elif tree Rustom Mody <rustompmody@gmail.com> - 2014-03-31 22:45 -0700
      Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 02:05 -0400
      Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 00:28 -0600
    Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 00:13 -0600
    Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 02:24 -0400
    Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 00:39 -0600
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 17:55 +1100
      Re: Code style query: multiple assignments in if/elif tree Steven D'Aprano <steve@pearwood.info> - 2014-04-01 07:29 +0000
        Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 18:49 +1100
        Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 02:29 -0600
        Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 19:56 +1100
    Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 03:21 -0400
    Re: Code style query: multiple assignments in if/elif tree Chris Angelico <rosuav@gmail.com> - 2014-04-01 18:26 +1100
    Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 03:34 -0400
    Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 03:39 -0400
    Re: Code style query: multiple assignments in if/elif tree David Hutto <dwightdhutto@gmail.com> - 2014-04-01 03:46 -0400
    Re: Code style query: multiple assignments in if/elif tree Ian Kelly <ian.g.kelly@gmail.com> - 2014-04-01 02:55 -0600

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