OrderedDict代表节俭

Question

我正在使用parsimonious来解析一些csv。我的问题是生成的输出没有按照预期的顺序输出。例如，如果输入字符串是

Load,File,Sample 

然后我希望得到：

import database from Sample

相反，我得到的是：

from Sample import database

对于我尝试的每个输入，这都是一个始终如一的问题:第一个令牌是条目OrderedDict中的最后一项，但我不知道为什么。

下面是我的代码：

from parsimonious.grammar import Grammar
from parsimonious.nodes import NodeVisitor
from collections import OrderedDict

class EntryParser(NodeVisitor):
    def __init__(self, grammar, text):
        self.entry = OrderedDict()
        ast = Grammar(grammar).parse(text)
        self.visit(ast)
    def visit_alt(self, n, vc):
        self.entry['alt'] = "alter "
    def visit_load(self, n, vc):
        self.entry['load'] = "import database "
    def visit_app(self, n, vc):
        self.entry['app'] = "application "
    def visit_db(self, n, vc):
        self.entry['db'] = "database "
    def visit_filter(self, n, vc):
        self.entry['filter'] = "filter "
    def visit_group(self, n, vc):
        self.entry['group'] = "group "
    def visit_obj(self, n, vc):
        self.entry['obj'] = "object "
    def visit_trigger(self, n, vc):
        self.entry['trigger'] = "trigger "
    def visit_user(self, n, vc):
        self.entry['user'] = "user "
    def visit_sql(self, n, vc):
        self.entry['sql'] = "connect as "
    def visit_file(self, n, vc):
        self.entry['file'] = "from "
    def visit_dbname(self, n, vc):
        self.entry['dbname'] = n.text + " "
    def generic_visit(self, n, vc):
        pass

grammar = """\
ts0 = alt / load
sep = ","
alt = "Alt" sep altdomain
altdomain = app / db / filter / group / obj / trigger / user
load = "Load" sep loaddomain
loaddomain = (sql / file) sep dbname
sql = "SQL"
file = "File"
app = "App"
db = "DB"
filter = "Filter"
group = "Group"
obj = "Object"
trigger = "Trigger"
user = "User"
dbname = ~"[A-z]+"
"""

text = """\
Alt,Filter
Alt,App
Alt,DB
Alt,Group,
Alt,Object
Alt,Trigger
Alt,User
Load,SQL,Sample
Load,File,Sample
"""

for line in text.splitlines():
    for v in EntryParser(grammar, line).entry.values():
        print(v, end="")
    print('\n')

Answer 1

我认为是OrderedDict造成了问题。只需使用常规字典而不是{}。

基本上将self.entry = OrderedDict()更改为self.entry = {}

同样，基于语法的解析工作方式，首先将匹配最里面的元素，然后它将移动到外部匹配的规则(根据返回值)。

因此，为了获得正确的顺序，您必须使用堆栈(或使用常规列表并颠倒数组)。