fastidious 0.1.dev0

用法

从 计算器示例 。 要阅读该示例，请考虑regex，除了or拼写为 文字字符用引号括起来，我们可以引用其他规则。

#! /usr/bin/pythonfromfastidiousimportParserclassCalculator(Parser):# __grammar__ is the PEG definition. Each `rulename <- a rule`# adds a method `Calculator.rulename()`. This methods tries to# match the input at current position__grammar__=r"""
    # the label is ommited. `:expr` is equivalent to `expr:expr`
    eval <- :expr EOF {@expr}

    # action {on_expr} calls `Calculator.on_expr(self, value, first, rest)`
    # on match. `first` and `rest` args are the labeled parts of the rule
    term <- first:factor rest:( _ mult_op _ factor )* {on_expr}

    # Because the Parser has a method named `on_expr` ("on_" + rulename)
    # this method is the implicit action of this rule. We omitted {on_expr}
    expr <- _ first:term rest:( _ add_op _ term  )* _

    # there's no explicit or implicit action. These rules return their exact
    # matches
    add_op <- '+' / '-'
    mult_op <- '*' / '/'

    # action {@fact} means : return only the match of part labeled `fact`.
    factor <- ( '(' fact:expr ')' ) / fact:integer {@fact}

    integer <- '-'? [0-9]+
    _ <- [ \n\t\r]*

    # this one is tricky. `.` means "any char". At EOF there's no char,
    # thus Not any char, thus `!.`
    EOF <- !.
    """defon_expr(self,value,first,rest):result=firstforrinrest:op=r[1]ifop=='+':result+=r[3]elifop=='-':result-=r[3]elifop=='*':result*=r[3]else:result/=r[3]returnresultdefon_integer(self,value):returnint(self.p_flatten(value))if__name__=="__main__":importsysc=Calculator("".join(sys.argv[1:]))result=c.eval()# because eval is the first rule defined in the grammar, it's the default rule.# We could call the classmethod `p_parse`:# result = Calculator.p_parse("".join(sys.argv[1:]))# The default entry point can be overriden setting the class attribute# `__default__`print(result)

那么您就拥有了一个成熟的、最先进的、仅限整数的计算器o/

examples/calculator.py "-21 *  ( 3 + 1 ) / -2"42

classParent(Parser):__grammar__=r"""
    some_as <- 'a'+
    """classChild(Parent):__grammar__=r"""
    letters <- some_as some_bs EOF {p_flatten}
    some_bs <- 'b'+
    EOF <- !.
    """assert(Child.p_parse("aabb")=="aabb")