A Temperature That Checks Itself · Python problem 407972

A lab's control software shows each tank's temperature in three units, and operators may type a new value in any of them. An earlier version stored all three numbers and they drifted apart whenever one was updated; it also happily accepted -500 °C.

Write a class Temperature(celsius=0.0) with these attributes, all used without brackets, like plain attributes:

celsius, fahrenheit and kelvin can be read and assigned. Assigning any of them changes the temperature, and the other two follow (F = C * 9 / 5 + 32, K = C + 273.15).
A temperature below absolute zero (0 K, which is -273.15 °C) raises ValueError, both in the constructor and on assignment, and leaves the temperature unchanged.
state is "ice" below 0 °C, "water" from 0 up to (not including) 100 °C, and "steam" from 100 °C. It can only be read: assigning to it raises AttributeError.

The tests use the helper session(ops, start) from the setup: it creates Temperature(start) and runs a list of steps, each ("set", name, value) (an assignment) or ("get", name) (a read), and returns one result per step (None for a successful assignment, the exception's name when one is raised).

Examples

Input:  session([("get", "fahrenheit"), ("set", "kelvin", 373.15), ("get", "celsius"),
                 ("get", "state"), ("set", "celsius", -300), ("get", "kelvin")], 20)
Output: [68.0, None, 100.0, 'steam', 'ValueError', 373.15]

Input:  session([("set", "state", "ice"), ("get", "state")], -5)
Output: ['AttributeError', 'ice']

Constraints

Values are numbers; floats are compared with a tolerance of 1e-6.
Exactly 0 K is allowed.

Goals

Store one value and compute the others on demand, so they can never go stale
Validate new values in a property setter
Make a derived value read-only