Source code for astropy.utils.state

"""
A simple class to manage a piece of global science state.  See
:ref:`astropy:config-developer` for more details.
"""


__all__ = ['ScienceState']


class _ScienceStateContext:
    def __init__(self, parent, value):
        self._value = value
        self._parent = parent

    def __enter__(self):
        pass

    def __exit__(self, type, value, tb):
        self._parent._value = self._value

    def __repr__(self):
        # Ensure we have a single-line repr, just in case our
        # value is not something simple like a string.
        value_repr, lb, _ = repr(self._parent._value).partition("\n")
        if lb:
            value_repr += "..."
        return f"<ScienceState {self._parent.__name__}: {value_repr}>"


[docs]class ScienceState: """ Science state subclasses are used to manage global items that can affect science results. Subclasses will generally override `validate` to convert from any of the acceptable inputs (such as strings) to the appropriate internal objects, and set an initial value to the ``_value`` member so it has a default. Examples -------- :: class MyState(ScienceState): @classmethod def validate(cls, value): if value not in ('A', 'B', 'C'): raise ValueError("Must be one of A, B, C") return value """ def __init__(self): raise RuntimeError("This class is a singleton. Do not instantiate.")
[docs] @classmethod def get(cls): """ Get the current science state value. """ return cls.validate(cls._value)
[docs] @classmethod def set(cls, value): """Set the current science state value.""" # Create context with current value ctx = _ScienceStateContext(cls, cls._value) # Set new value value = cls.validate(value) cls._value = value # Return context manager return ctx
[docs] @classmethod def validate(cls, value): """ Validate the value and convert it to its native type, if necessary. """ return value