pyeval_operator.py

"""
operator.py - implements an operator class for use by the evaluator

AUTHOR: Jon Fincher
"""

# Dictionary lookup for precedence
# Currently four levels of precedence
PRECEDENCE = {
    '+' : 2,            # Addition
    '-' : 2,            # Subtraction
    '*' : 3,            # Multiplication
    '/' : 3,            # Division
    '%' : 3,            # Modulo
    '^' : 4             # Power
}

# Dictionary lookup for number of operands to use
OPERAND_COUNT = {
    '+' : 2,            # Addition
    '-' : 2,            # Subtraction
    '*' : 2,            # Multiplication
    '/' : 2,            # Division
    '%' : 2,            # Modulo
    '^' : 2             # Power
}

class Operator:
    """
    Common operator class used by the evaluator.
    """

    _op_string = ""      # String to hold the operator
    _op_prec = 0         # Integer to hold the precedence
    _op_cnt = 0          # Integer to hold the number of operands to use

    def __init__(self, operator_string):
        """ Create a new operator object. """
        self._op_string = operator_string
        self._op_prec = PRECEDENCE[self._op_string]
        self._op_cnt = OPERAND_COUNT[self._op_string]

    @property
    def op_string(self):
        return self._op_string

    @op_string.setter
    def op_string(self, new_op_string):
        self._op_string = new_op_string
        self._op_prec = PRECEDENCE[self._op_string]
        self._op_cnt = OPERAND_COUNT[self._op_string]

    @property
    def count(self):
        return self._op_cnt

    @property
    def precedence(self):
        return self._op_prec