PyParsing:Combine()有什么作用? [英] PyParsing: What does Combine() do?

问题描述

两者之间有什么区别

foo = TOKEN1 + TOKEN2

和

foo = Combine(TOKEN1 + TOKEN2)

谢谢.

更新:根据我的实验，Combine()似乎是用于终端的，您要在其中构建要匹配的表达式，而普通的+则是用于非终端的.但是我不确定.

UPDATE: Based on my experimentation, it seems like Combine() is for terminals, where you're trying to build an expression to match on, whereas plain + is for non-terminals. But I'm not sure.

推荐答案

合并有2种效果:

• 它将所有标记连接到一个字符串中

• it concatenates all the tokens into a single string

它要求匹配的令牌都必须相邻且没有空格

it requires the matching tokens to all be adjacent with no intervening whitespace

如果创建类似

realnum = Word(nums) + "." + Word(nums)

然后realnum.parseString("3.14")将返回3个令牌的列表:前导'3'，'.'和后缀'14'.但是，如果将其包装在Combine中，例如:

Then realnum.parseString("3.14") will return a list of 3 tokens: the leading '3', the '.', and the trailing '14'. But if you wrap this in Combine, as in:

realnum = Combine(Word(nums) + "." + Word(nums))

然后，realnum.parseString("3.14")将返回"3.14"(然后您可以使用解析动作将其转换为浮点数).而且由于Combine禁止pyparsing的默认空白在标记之间跳过，因此您不会在答案为3.14是下一个答案"中偶然发现"3.14".

then realnum.parseString("3.14") will return '3.14' (which you could then convert to a float using a parse action). And since Combine suppresses pyparsing's default whitespace skipping between tokens, you won't accidentally find "3.14" in "The answer is 3. 14 is the next answer."

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