問(wèn)題描述

當(dāng)解析XML文檔格式為:

When parsing XML documents in the format of:

<Car>
    <Color>Blue</Color>
    <Make>Chevy</Make>
    <Model>Camaro</Model>
</Car>

我使用以下代碼:

carData = element.xpath('//Root/Foo/Bar/Car/node()[text()]')
parsedCarData = [{field.tag: field.text for field in carData} for action in carData]
print parsedCarData[0]['Color'] #Blue

如果標(biāo)簽為空，則此代碼將不起作用，例如:

This code will not work if a tag is empty such as :

<Car>
    <Color>Blue</Color>
    <Make>Chevy</Make>
    <Model/>
</Car>

使用與上面相同的代碼:

Using the same code as above:

carData = element.xpath('//Root/Foo/Bar/Car/node()[text()]')
parsedCarData = [{field.tag: field.text for field in carData} for action in carData]
print parsedCarData[0]['Model'] #Key Error

我將如何解析這個(gè)空白標(biāo)簽.

How would I parse this blank tag.

推薦答案

您正在放入一個(gè) [text()] 過(guò)濾器，該過(guò)濾器僅顯式詢問(wèn)具有文本節(jié)點(diǎn)的元素...然后當(dāng)它沒(méi)有給你沒(méi)有文本節(jié)點(diǎn)的元素時(shí)你會(huì)不高興?

You're putting in a [text()] filter which explicitly asks only for elements which have text nodes them... and then you're unhappy when it doesn't give you elements without text nodes?

去掉那個(gè)過(guò)濾器，你會(huì)得到你的模型元素:

Leave that filter out, and you'll get your model element:

>>> s='''
... <root>
...   <Car>
...     <Color>Blue</Color>
...     <Make>Chevy</Make>
...     <Model/>
...   </Car>
... </root>'''
>>> e = lxml.etree.fromstring(s)
>>> carData = e.xpath('Car/node()')
>>> carData
[<Element Color at 0x23a5460>, <Element Make at 0x23a54b0>, <Element Model at 0x23a5500>]
>>> dict(((e.tag, e.text) for e in carData))
{'Color': 'Blue', 'Make': 'Chevy', 'Model': None}

也就是說(shuō)——如果你的直接目標(biāo)是遍歷樹(shù)中的節(jié)點(diǎn)，你可以考慮使用 lxml.etree.iterparse() 代替，這將避免嘗試構(gòu)建完整的 DOM樹(shù)在內(nèi)存中，否則比構(gòu)建樹(shù)然后使用 XPath 對(duì)其進(jìn)行迭代要高效得多.(想想 SAX，但沒(méi)有瘋狂和痛苦的 API).

That said -- if your immediate goal is to iterate over the nodes in the tree, you might consider using lxml.etree.iterparse() instead, which will avoid trying to build a full DOM tree in memory and otherwise be much more efficient than building a tree and then iterating over it with XPath. (Think SAX, but without the insane and painful API).

使用 iterparse 實(shí)現(xiàn)可能如下所示:

Implementing with iterparse could look like this:

def get_cars(infile):
    in_car = False
    current_car = {}
    for (event, element) in lxml.etree.iterparse(infile, events=('start', 'end')):
        if event == 'start':
            if element.tag == 'Car':
                in_car = True
                current_car = {}
            continue
        if not in_car: continue
        if element.tag == 'Car':
            yield current_car
            continue
        current_car[element.tag] = element.text

for car in get_cars(infile = cStringIO.StringIO('''<root><Car><Color>Blue</Color><Make>Chevy</Make><Model/></Car></root>''')):
  print car

...這是更多代碼，但是(如果我們不使用 StringIO 作為示例)它可以處理比內(nèi)存容量大得多的文件.

...it's more code, but (if we weren't using StringIO for the example) it could process a file much larger than could fit in memory.

這篇關(guān)于使用 LXML 和 Python 解析空白 XML 標(biāo)簽的文章就介紹到這了，希望我們推薦的答案對(duì)大家有所幫助，也希望大家多多支持html5模板網(wǎng)！