[英]Setting the maximum number occurrences with `delimitedList` using pyparsing
pyparsing provides a helper function, delimitedList , that matches a sequence of one or more expressions , separated with a delimiter : pyparsing提供了一个辅助函数delimitedList ,它匹配一个或多个表达式的序列,用分隔符分隔:
delimitedList(expr, delim=',', combine=False)
How can this be used to match a sequence of expressions, where each expression may occur zero or one times?这如何用于匹配一系列表达式,其中每个表达式可能出现零次或一次?
For example, to match "foo", "bar, "baz"
I took a bottom-up approach a created a token for each word:例如,为了匹配"foo", "bar, "baz"
我采用了自下而上的方法,为每个单词创建了一个标记:
import pyparsing as pp
dbl_quote = pp.Suppress('"')
foo = dbl_quote + pp.Literal('foo') + dbl_quote
bar = dbl_quote + pp.Literal('bar') + dbl_quote
baz = dbl_quote + pp.Literal('baz') + dbl_quote
I want to create an expression that matches:我想创建一个匹配的表达式:
zero or one occurrences of
"foo"
, zero or one occurrences of"bar"
, zero or one occurrences of"baz"
零或一次出现"foo"
,零或一个事件"bar"
,零个或一个出现"baz"
... in any order . ...以任何顺序。 Examples of valid input:有效输入示例:
"foo", "bar", "baz"
"baz", "bar", "foo",
// Order is unimportant "baz", "bar", "foo",
// 顺序不重要"bar", "baz"
// Zero occurrences allowed "bar", "baz"
// 允许出现零次"baz"
// Zero occurrences of all tokens // 所有标记的出现次数为零Examples of invalid input:无效输入示例:
"notfoo", "notbar", "notbaz"
"foo", "foo", "bar", "baz"
// Two occurrences of foo
"foo", "foo", "bar", "baz"
// foo
出现两次"foo" "bar", "baz"
// Missing comma "foo" "bar", "baz"
// 缺少逗号"foo" "bar", "baz",
// Trailing comma "foo" "bar", "baz",
// 尾随逗号I gravitated towards delimitedList because my input is a comma delimited list, but now I feel this function is working against me rather than for me.我倾向于delimitedList因为我的输入是一个逗号分隔的列表,但现在我觉得这个功能对我不利,而不是对我有用。
import pyparsing as pp
dbl_quote = pp.Suppress('"')
foo = dbl_quote + pp.Literal('foo') + dbl_quote
bar = dbl_quote + pp.Literal('bar') + dbl_quote
baz = dbl_quote + pp.Literal('baz') + dbl_quote
# This is NOT what I want because it allows tokens
# to occur more than once.
foobarbaz = pp.delimitedList(foo | bar | baz)
if __name__ == "__main__":
TEST = '"foo", "bar", "baz"'
results = foobarbaz.parseString(TEST)
results.pprint()
Ordinarily, when I see "in any order" as part of a grammar, my first thought is to use Each
, which you can create with the &
operator:通常,当我看到“以任何顺序”作为语法的一部分时,我的第一个想法是使用Each
,您可以使用&
运算符创建它:
undelimited_foo_bar_baz = foo & bar & baz
This parser would parse foo
, bar
, and baz
in any order.这个解析器会以任何顺序解析foo
、 bar
和baz
。 If you wanted them to be optional, then simply wrap them in Optional:如果您希望它们是可选的,那么只需将它们包装在 Optional 中:
undelimited_foo_bar_baz = Optional(foo) & Optional(bar) & Optional(baz)
But the intervening commas in your input make this kind of messy, so as a fallback, you can stick with the delimitedList
(which will strip out the commas) add a condition parse action to get run after the list is parsed, to verify that only one of each of the matched items was present:但是输入中的中间逗号会使这种混乱,因此作为后备,您可以坚持使用delimitedList
(它将去除逗号)添加条件解析操作以在解析列表后运行,以验证仅存在每个匹配项目中的一个:
from collections import Counter
def no_more_than_one_of_any(t):
return all(freq == 1 for freq in Counter(t.asList()).values())
foobarbaz.addCondition(no_more_than_one_of_any, message="duplicate item found in list")
if __name__ == "__main__":
tests = '''\
"foo"
"bar"
"baz"
"foo", "baz"
"foo", "bar", "baz"
"foo", "bar", "baz", "foo"
'''
foobarbaz.runTests(tests)
Prints:印刷:
"foo"
['foo']
"bar"
['bar']
"baz"
['baz']
"foo", "baz"
['foo', 'baz']
"foo", "bar", "baz"
['foo', 'bar', 'baz']
"foo", "bar", "baz", "foo"
^
FAIL: duplicate item found in list, found '"' (at char 0), (line:1, col:1)
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