choiceField.py

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# 
# LSST Data Management System
# Copyright 2008, 2009, 2010 LSST Corporation.
# 
# This product includes software developed by the
# LSST Project (http://www.lsst.org/).
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
# 
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
# 
# You should have received a copy of the LSST License Statement and 
# the GNU General Public License along with this program.  If not, 
# see <http://www.lsstcorp.org/LegalNotices/>.
#
import traceback

from .config import Field, _typeStr

__all__ = ["ChoiceField"]

class ChoiceField(Field):
    """
    Defines a Config Field which allows only a set of values
    All allowed must be of the same type.
    Allowed values should be provided as a dict of value, doc string pairs

    """
    def __init__(self, doc, dtype, allowed, default=None, optional=True):
        self.allowed = dict(allowed)
        if optional and None not in self.allowed: 
            self.allowed[None]="Field is optional"

        if len(self.allowed)==0:
            raise ValueError("ChoiceFields must allow at least one choice")
        
        doc += "\nAllowed values:\n"
        for choice, choiceDoc in self.allowed.iteritems():
            if choice is not None and not isinstance(choice, dtype):
                raise ValueError("ChoiceField's allowed choice %s is of incorrect type %s. Expected %s"%\
                        (choice, _typeStr(choice), _typeStr(dtype)))
            doc += "\t%s\t%s\n"%(str(choice), choiceDoc)

        Field.__init__(self, doc=doc, dtype=dtype, default=default, 
                check=None, optional=optional)
        self.source = traceback.extract_stack(limit=2)[0]

    def _validateValue(self, value):
        Field._validateValue(self, value)
        if value not in self.allowed:
            allowedStr = "{%s"%self.allowed.keys()[0]
            for x in self.allowed:
                allowedStr += ", %s"%x
            allowedStr+="}"
            msg = "Value %s is not allowed.\n\tAllowed values: %s"%\
                    (value, allowedStr)
            raise ValueError(msg)