direct.py 文件源码

def grammar():
    """Define the query grammar.

    Backus-Naur form (BNF) of the grammar::

        <grammar> ::= <item> | <item> <boolean> <grammar>
           <item> ::= <hosts> | "(" <grammar> ")"
        <boolean> ::= "and not" | "and" | "xor" | "or"

    Given that the pyparsing library defines the grammar in a BNF-like style, for the details of the tokens not
    specified above check directly the source code.

    Returns:
        pyparsing.ParserElement: the grammar parser.

    """
    # Boolean operators
    boolean = (pp.CaselessKeyword('and not').leaveWhitespace() | pp.CaselessKeyword('and') |
               pp.CaselessKeyword('xor') | pp.CaselessKeyword('or'))('bool')

    # Parentheses
    lpar = pp.Literal('(')('open_subgroup')
    rpar = pp.Literal(')')('close_subgroup')

    # Hosts selection: clustershell (,!&^[]) syntax is allowed: host10[10-42].domain
    hosts = (~(boolean) + pp.Word(pp.alphanums + '-_.,!&^[]'))('hosts')

    # Final grammar, see the docstring for its BNF based on the tokens defined above
    # Groups are used to split the parsed results for an easy access
    full_grammar = pp.Forward()
    item = hosts | lpar + full_grammar + rpar
    full_grammar << pp.Group(item) + pp.ZeroOrMore(pp.Group(boolean + item))  # pylint: disable=expression-not-assigned

    return full_grammar