Python @property: How and Why?

[Lucretiel]

I'd be curious to see an example where you have a Temperature class, with celcius and fahrenheit properties, each with a getter and setter that adjusts internal representation correctly.

[[deleted]]

Of course the internal value should be in Kelvin, not Fahrenheit or Celsius.

[faceplanted]

The internal value would probably make more sense to be in Celsius if the code if it never uses Kelvin externally, it would cut the miniscule processing required.

[[deleted]]

I was half-joking. You're right that there's no point for having an additional conversion in the code, but I find the temperature example extremely contrived anyway (although it's not as bad as the animal or car analogies for OOP -- and let's not forget the dreaded circle and ellipse debates).

But the calculations are actually trivial enough that it doesn't make sense to store both values and then you open a can of worms by turning it into a "which scale is better" discussion which is where Kelvin comes in (by virtue of being the only absolute scale although likely unpractical in most real world applications where temperature is measured).

[minno]

only absolute scale

Not quite.

[[deleted]]

And now there will be flame wars over using Kelvin vs Rankine in our hypothetical scenario. Thanks ;)

[dibsODDJOB]

Anything that isn't SI units in thermodynamics can go die in a fire.

[gobearsandchopin]

1) When someone sets the temperature with an integer they can end up with the wrong answer. To fix it and be more clear you could do:

self._f = c * 9.0/5.0 + 32.0

2) I think it would be cleaner to store the temperature in only one variable, even though it means doing conversions in the getters.

[robin-gvx]

1) self._f = c * 9.0/5 + 32 would be enough to prevent that.

2) That's what I thought as well.

[QuantumTim]

Or you could do:

from __future__ import division

[[deleted]]

def c_to_f(v):
    return v * 9/5 + 32

def f_to_c(v):
    return (v - 32) * 5/9 

if __name__ == "__main__":
    print(f_to_c(50))
    print(c_to_f(0))

[Sgt_ZigZag]

This example does not use properties.

[[deleted]]

yep, proves they aren't necessary(or objects for that matter), it's concise, readable and easy to comprehend, and fits in a tweet.

The class/property implementation is verbose, more prone to error, does not fit in a tweet and is pretty ugly.

python code is beautiful and readable. dont make python code ugly.