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