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"""
A simple class to manage a piece of global science state. See
:ref:`config-developer` for more details.
"""
__all__ = ['ScienceState']
class ScienceState(object):
"""
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.")
@classmethod
def get(cls):
"""
Get the current science state value.
"""
return cls.validate(cls._value)
@classmethod
def set(cls, value):
"""
Set the current science state value.
"""
class _Context(object):
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):
return ('<ScienceState {0}: {1!r}>'
.format(self._parent.__name__, self._parent._value))
ctx = _Context(cls, cls._value)
value = cls.validate(value)
cls._value = value
return ctx
@classmethod
def validate(cls, value):
"""
Validate the value and convert it to its native type, if
necessary.
"""
return value
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