parameter.py

""" Contains the Parameter class.

    Copyright (c) 2014 Kenn Takara
    See LICENSE for details

"""

from sympy import Symbol
from builtins import range


from pysolve import InvalidNameError
from pysolve.variable import Variable


class Parameter(Symbol):
    """ This class contains a 'parameter'.  This is an exogenous
        variable.  The solver is not allowed to change this value
        when solving a set of equations.

        Attributes:
            symbol:
            name:
            desc:
            default:
            value:
    """
    # pylint: disable=too-many-ancestors

    def __init__(self, name, desc=None, default=None):
        if name in Variable.ILLEGAL_NAMES:
            raise InvalidNameError(name, 'Name already used by sympy')

        super().__init__()
        self.name = name
        self.desc = desc
        self.default = default
        self.model = None

        self._index = None
        self._value = default

    @property
    def value(self):
        """ Getter accessor for parameter value """
        return self._value

    @value.setter
    def value(self, val):
        """ Setter accessor for parameter value """
        self._value = val


class SeriesParameter(Parameter):
    """ A parameter that can access the previous solution values.

        Attributes:
            name:
            variable:
            iteration:
            default:
    """
    # pylint: disable=too-many-ancestors

    def __init__(self, name, variable=None, iteration=None, default=None):
        super(SeriesParameter, self).__init__(name, default=default)
        if variable is None or iteration is None:
            raise ValueError('variable and iteration cannot be none')
        self.variable = variable
        self.iteration = iteration

    @property
    def value(self):
        """ Returns the value of a variable at a another iteration.

            If the iteration value is out-of-range, the variable's
            default value is returned.
        """
        try:
            return self.variable.model.get_value(
                self.variable, self.iteration)
        except IndexError:
            return self.variable.value or self.variable.default