expression.py 文件源码

def __init__(self):
        """
        Create a parser that parse arithmetic expressions. They can
        contains variable identifiers or raw numbers. The meaning
        for the identifiers is left to the
        """
        number = p.Regex(r'\d+(\.\d*)?([eE]\d+)?')
        identifier = p.Word(p.alphas)
        terminal = identifier | number
        self._expr = p.infixNotation(terminal, [
            (p.oneOf('* /'), 2, p.opAssoc.LEFT),
            (p.oneOf('+ -'), 2, p.opAssoc.LEFT)
        ]) + p.stringEnd()