我想对一组 XML 文档进行一些交互式探索。我正在尝试使用 lxml 解析文档并使用它的 find、findall 和 xpath 方法进行查询。但是，当我尝试创建 Element 对象的 RDD 时，PySpark 阻塞了:
from lxml import etree
from lxml.etree import XMLSyntaxError
def get_root(xml):
xml_bytes = bytes(bytearray(xml, encoding = 'utf-8'))
try:
return [etree.XML(xml_bytes)]
except XMLSyntaxError:
return []
docs = [
"<doc><tag name='hoo'>hah</tag><tag name='wah'>zoo</tag></doc>"
, "<doc><tag name='hoo'>yah</tag><tag name='wah'>woo</tag></doc>"
]
roots = [get_root(x)[0] for x in docs]
roots
[<Element doc at 0x3b2280>, <Element doc at 0x3b2140>]
docs_rdd = sc.parallelize(docs)
roots_rdd = docs_rdd.flatMap(lambda d: get_root(d))
roots_rdd.count()
2
roots_rdd.first()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "lxml.etree.pyx", line 1033, in lxml.etree._Element.__repr__ (src/lxml/lxml.etree.c:42268)
File "lxml.etree.pyx", line 881, in lxml.etree._Element.tag.__get__ (src/lxml/lxml.etree.c:40855)
File "apihelpers.pxi", line 15, in lxml.etree._assertValidNode (src/lxml/lxml.etree.c:12875)
AssertionError: invalid Element proxy at 62728864
有人可以帮助我了解这里发生了什么吗？
Python 2.7.x 或 3.5.x，Spark 1.6.x，lxml 安装有 pip 或 pip3。
提前致谢!
请您参考如下方法:
lxml 对象不可序列化，不能在执行器和驱动程序之间传递或打乱。完全无需使用 Spark 即可轻松重现:
from lxml import etree
import pickle
pickle.loads(pickle.dumps(etree.XML("<doc>foo</doc>")))
AssertionError Traceback (most recent call last)
...
AssertionError: invalid Element proxy at ...
您仍然可以使用 lxml 来解析和获取可序列化的 Python 对象:
from operator import attrgetter
docs_rdd.flatMap(get_root).flatMap(lambda x: x).map(attrgetter("text")).collect()
['hah', 'zoo', 'yah', 'woo']
