问题：熊猫read_xml（）方法测试策略
当前，pandas I / O工具没有维护read_xml()方法，而相应的工具to_xml()。但是，read_json证明可以为数据帧导入和read_html标记格式实现树状结构。
如果大熊猫团队会考虑这样一个read_xml为未来大熊猫版本的方法，他们会追求什么实现：使用内置的解析xml.etree.ElementTree其iterfind()或iterparse()功能或第三方模块，lxml其XPath 1.0和XSLT 1.0的方法呢？
以下是我在简单，扁平，以元素为中心的XML输入上针对四种方法类型的测试运行。所有这些都针对root的任何第二级子级进行了通用解析，并且每种方法都应产生完全相同的pandas数据帧。除最后一次调用外pd.Dataframe()，所有其他功能都在词典列表中。XSLT方法将XML转换为CSV，以便StringIO()在中进行转换pd.read_csv()。
问题 （多部分）
性能：您如何解释由于
iterparse迭代解析文件而通常建议对较大文件使用的速度较慢的速度？部分原因是由于if逻辑检查吗？内存：CPU内存是否与I / O调用中的时间相关？XSLT和XPath 1.0在较大的XML文档中往往无法很好地扩展，因为必须在内存中读取整个文件才能进行解析。
策略：词典列表是
Dataframe()呼叫的最佳策略吗？请参阅以下有趣的答案：生成器版本和iterwalk用户定义版本。两个上载列表到数据帧。
输入数据（Stack Overflow当前的年度最大用户，其中包括我们的熊猫朋友）
<?xml version="1.0" encoding="utf-8"?>
<stackoverflow>
<topusers>
<user>Gordon Linoff</user>
<link>http://www.stackoverflow.com//users/1144035/gordon-linoff</link>
<location>New York, United States</location>
<year_rep>5,985</year_rep>
<total_rep>499,408</total_rep>
<tag1>sql</tag1>
<tag2>sql-server</tag2>
<tag3>mysql</tag3>
</topusers>
<topusers>
<user>Günter Zöchbauer</user>
<link>http://www.stackoverflow.com//users/217408/g%c3%bcnter-z%c3%b6chbauer</link>
<location>Linz, Austria</location>
<year_rep>5,835</year_rep>
<total_rep>154,439</total_rep>
<tag1>angular2</tag1>
<tag2>typescript</tag2>
<tag3>javascript</tag3>
</topusers>
<topusers>
<user>jezrael</user>
<link>http://www.stackoverflow.com//users/2901002/jezrael</link>
<location>Bratislava, Slovakia</location>
<year_rep>5,740</year_rep>
<total_rep>83,237</total_rep>
<tag1>pandas</tag1>
<tag2>python</tag2>
<tag3>dataframe</tag3>
</topusers>
<topusers>
<user>VonC</user>
<link>http://www.stackoverflow.com//users/6309/vonc</link>
<location>France</location>
<year_rep>5,577</year_rep>
<total_rep>651,397</total_rep>
<tag1>git</tag1>
<tag2>github</tag2>
<tag3>docker</tag3>
</topusers>
<topusers>
<user>Martijn Pieters</user>
<link>http://www.stackoverflow.com//users/100297/martijn-pieters</link>
<location>Cambridge, United Kingdom</location>
<year_rep>5,337</year_rep>
<total_rep>525,176</total_rep>
<tag1>python</tag1>
<tag2>python-3.x</tag2>
<tag3>python-2.7</tag3>
</topusers>
<topusers>
<user>T.J. Crowder</user>
<link>http://www.stackoverflow.com//users/157247/t-j-crowder</link>
<location>United Kingdom</location>
<year_rep>5,258</year_rep>
<total_rep>508,310</total_rep>
<tag1>javascript</tag1>
<tag2>jquery</tag2>
<tag3>java</tag3>
</topusers>
<topusers>
<user>akrun</user>
<link>http://www.stackoverflow.com//users/3732271/akrun</link>
<location></location>
<year_rep>5,188</year_rep>
<total_rep>229,553</total_rep>
<tag1>r</tag1>
<tag2>dplyr</tag2>
<tag3>dataframe</tag3>
</topusers>
<topusers>
<user>Wiktor Stribi?ew</user>
<link>http://www.stackoverflow.com//users/3832970/wiktor-stribi%c5%bcew</link>
<location>Warsaw, Poland</location>
<year_rep>4,948</year_rep>
<total_rep>158,134</total_rep>
<tag1>regex</tag1>
<tag2>javascript</tag2>
<tag3>c#</tag3>
</topusers>
<topusers>
<user>Darin Dimitrov</user>
<link>http://www.stackoverflow.com//users/29407/darin-dimitrov</link>
<location>Sofia, Bulgaria</location>
<year_rep>4,936</year_rep>
<total_rep>709,683</total_rep>
<tag1>c#</tag1>
<tag2>asp.net-mvc</tag2>
<tag3>asp.net-mvc-3</tag3>
</topusers>
<topusers>
<user>Eric Duminil</user>
<link>http://www.stackoverflow.com//users/6419007/eric-duminil</link>
<location></location>
<year_rep>4,854</year_rep>
<total_rep>12,557</total_rep>
<tag1>ruby</tag1>
<tag2>ruby-on-rails</tag2>
<tag3>arrays</tag3>
</topusers>
<topusers>
<user>alecxe</user>
<link>http://www.stackoverflow.com//users/771848/alecxe</link>
<location>New York, United States</location>
<year_rep>4,723</year_rep>
<total_rep>233,368</total_rep>
<tag1>python</tag1>
<tag2>selenium</tag2>
<tag3>protractor</tag3>
</topusers>
<topusers>
<user>Jean-François Fabre</user>
<link>http://www.stackoverflow.com//users/6451573/jean-fran%c3%a7ois-fabre</link>
<location>Toulouse, France</location>
<year_rep>4,526</year_rep>
<total_rep>30,027</total_rep>
<tag1>python</tag1>
<tag2>python-3.x</tag2>
<tag3>python-2.7</tag3>
</topusers>
<topusers>
<user>piRSquared</user>
<link>http://www.stackoverflow.com//users/2336654/pirsquared</link>
<location>Bellevue, WA, United States</location>
<year_rep>4,482</year_rep>
<total_rep>41,183</total_rep>
<tag1>pandas</tag1>
<tag2>python</tag2>
<tag3>dataframe</tag3>
</topusers>
<topusers>
<user>CommonsWare</user>
<link>http://www.stackoverflow.com//users/115145/commonsware</link>
<location>Who Wants to Know?</location>
<year_rep>4,475</year_rep>
<total_rep>616,135</total_rep>
<tag1>android</tag1>
<tag2>java</tag2>
<tag3>android-intent</tag3>
</topusers>
<topusers>
<user>Quentin</user>
<link>http://www.stackoverflow.com//users/19068/quentin</link>
<location>United Kingdom</location>
<year_rep>4,464</year_rep>
<total_rep>509,365</total_rep>
<tag1>javascript</tag1>
<tag2>html</tag2>
<tag3>css</tag3>
</topusers>
<topusers>
<user>Jon Skeet</user>
<link>http://www.stackoverflow.com//users/22656/jon-skeet</link>
<location>Reading, United Kingdom</location>
<year_rep>4,348</year_rep>
<total_rep>921,690</total_rep>
<tag1>c#</tag1>
<tag2>java</tag2>
<tag3>.net</tag3>
</topusers>
<topusers>
<user>Felix Kling</user>
<link>http://www.stackoverflow.com//users/218196/felix-kling</link>
<location>Sunnyvale, CA</location>
<year_rep>4,324</year_rep>
<total_rep>411,535</total_rep>
<tag1>javascript</tag1>
<tag2>jquery</tag2>
<tag3>asynchronous</tag3>
</topusers>
<topusers>
<user>matt</user>
<link>http://www.stackoverflow.com//users/341994/matt</link>
<location></location>
<year_rep>4,313</year_rep>
<total_rep>220,515</total_rep>
<tag1>swift</tag1>
<tag2>ios</tag2>
<tag3>xcode</tag3>
</topusers>
<topusers>
<user>Psidom</user>
<link>http://www.stackoverflow.com//users/4983450/psidom</link>
<location>Atlanta, GA, United States</location>
<year_rep>4,236</year_rep>
<total_rep>36,950</total_rep>
<tag1>python</tag1>
<tag2>pandas</tag2>
<tag3>r</tag3>
</topusers>
<topusers>
<user>Martin R</user>
<link>http://www.stackoverflow.com//users/1187415/martin-r</link>
<location>Germany</location>
<year_rep>4,195</year_rep>
<total_rep>269,380</total_rep>
<tag1>swift</tag1>
<tag2>ios</tag2>
<tag3>swift3</tag3>
</topusers>
<topusers>
<user>Barmar</user>
<link>http://www.stackoverflow.com//users/1491895/barmar</link>
<location>Arlington, MA</location>
<year_rep>4,179</year_rep>
<total_rep>289,989</total_rep>
<tag1>javascript</tag1>
<tag2>php</tag2>
<tag3>jquery</tag3>
</topusers>
<topusers>
<user>Alexey Mezenin</user>
<link>http://www.stackoverflow.com//users/1227923/alexey-mezenin</link>
<location>??????</location>
<year_rep>4,142</year_rep>
<total_rep>31,602</total_rep>
<tag1>laravel</tag1>
<tag2>php</tag2>
<tag3>laravel-5.3</tag3>
</topusers>
<topusers>
<user>BalusC</user>
<link>http://www.stackoverflow.com//users/157882/balusc</link>
<location>Amsterdam, Netherlands</location>
<year_rep>4,046</year_rep>
<total_rep>703,046</total_rep>
<tag1>java</tag1>
<tag2>jsf</tag2>
<tag3>servlets</tag3>
</topusers>
<topusers>
<user>GurV</user>
<link>http://www.stackoverflow.com//users/6348498/gurv</link>
<location></location>
<year_rep>4,016</year_rep>
<total_rep>7,932</total_rep>
<tag1>sql</tag1>
<tag2>mysql</tag2>
<tag3>sql-server</tag3>
</topusers>
<topusers>
<user>Nina Scholz</user>
<link>http://www.stackoverflow.com//users/1447675/nina-scholz</link>
<location>Berlin, Deutschland</location>
<year_rep>3,950</year_rep>
<total_rep>61,135</total_rep>
<tag1>javascript</tag1>
<tag2>arrays</tag2>
<tag3>object</tag3>
</topusers>
<topusers>
<user>JB Nizet</user>
<link>http://www.stackoverflow.com//users/571407/jb-nizet</link>
<location>Saint-Etienne, France</location>
<year_rep>3,923</year_rep>
<total_rep>418,780</total_rep>
<tag1>java</tag1>
<tag2>hibernate</tag2>
<tag3>java-8</tag3>
</topusers>
<topusers>
<user>Frank van Puffelen</user>
<link>http://www.stackoverflow.com//users/209103/frank-van-puffelen</link>
<location>San Francisco, CA</location>
<year_rep>3,920</year_rep>
<total_rep>86,520</total_rep>
<tag1>firebase</tag1>
<tag2>firebase-database</tag2>
<tag3>android</tag3>
</topusers>
<topusers>
<user>dasblinkenlight</user>
<link>http://www.stackoverflow.com//users/335858/dasblinkenlight</link>
<location>United States</location>
<year_rep>3,886</year_rep>
<total_rep>475,813</total_rep>
<tag1>c#</tag1>
<tag2>java</tag2>
<tag3>c++</tag3>
</topusers>
<topusers>
<user>Tim Biegeleisen</user>
<link>http://www.stackoverflow.com//users/1863229/tim-biegeleisen</link>
<location>Singapore</location>
<year_rep>3,814</year_rep>
<total_rep>77,211</total_rep>
<tag1>sql</tag1>
<tag2>mysql</tag2>
<tag3>java</tag3>
</topusers>
<topusers>
<user>Greg Hewgill</user>
<link>http://www.stackoverflow.com//users/893/greg-hewgill</link>
<location>Christchurch, New Zealand</location>
<year_rep>3,796</year_rep>
<total_rep>529,137</total_rep>
<tag1>git</tag1>
<tag2>python</tag2>
<tag3>git-pull</tag3>
</topusers>
<topusers>
<user>unutbu</user>
<link>http://www.stackoverflow.com//users/190597/unutbu</link>
<location></location>
<year_rep>3,735</year_rep>
<total_rep>401,595</total_rep>
<tag1>python</tag1>
<tag2>pandas</tag2>
<tag3>numpy</tag3>
</topusers>
<topusers>
<user>Hans Passant</user>
<link>http://www.stackoverflow.com//users/17034/hans-passant</link>
<location>Madison, WI</location>
<year_rep>3,688</year_rep>
<total_rep>672,118</total_rep>
<tag1>c#</tag1>
<tag2>.net</tag2>
<tag3>winforms</tag3>
</topusers>
<topusers>
<user>Jonathan Leffler</user>
<link>http://www.stackoverflow.com//users/15168/jonathan-leffler</link>
<location>California, USA</location>
<year_rep>3,649</year_rep>
<total_rep>455,157</total_rep>
<tag1>c</tag1>
<tag2>bash</tag2>
<tag3>unix</tag3>
</topusers>
<topusers>
<user>paxdiablo</user>
<link>http://www.stackoverflow.com//users/14860/paxdiablo</link>
<location></location>
<year_rep>3,636</year_rep>
<total_rep>507,043</total_rep>
<tag1>c</tag1>
<tag2>c++</tag2>
<tag3>bash</tag3>
</topusers>
<topusers>
<user>Pranav C Balan</user>
<link>http://www.stackoverflow.com//users/3037257/pranav-c-balan</link>
<location>Ramanthali, Kannur, Kerala, India</location>
<year_rep>3,604</year_rep>
<total_rep>64,476</total_rep>
<tag1>javascript</tag1>
<tag2>jquery</tag2>
<tag3>html</tag3>
</topusers>
<topusers>
<user>Suragch</user>
<link>http://www.stackoverflow.com//users/3681880/suragch</link>
<location>Hohhot, China</location>
<year_rep>3,580</year_rep>
<total_rep>71,032</total_rep>
<tag1>swift</tag1>
<tag2>ios</tag2>
<tag3>android</tag3>
</topusers>
</stackoverflow>
Python方法
import xml.etree.ElementTree as et
import pandas as pd
from io import StringIO
from lxml import etree as lxet
def read_xml_iterfind():
tree = et.parse('Input.xml')
data = []
inner = {}
for el in tree.iterfind('./*'):
for i in el.iterfind('*'):
inner[i.tag] = i.text
data.append(inner)
inner = {}
df = pd.DataFrame(data)
def read_xml_iterparse():
data = []
inner = {}
i = 1
for (ev, el) in et.iterparse(path):
if i <= 2:
first_tag = el.tag
if el.tag == first_tag and len(inner) != 0:
data.append(inner)
inner = {}
if el.text is not None and len(el.text.strip()) > 0:
inner[el.tag] = el.text
i += 1
df = pd.DataFrame(data)
def read_xml_lxml_xpath():
tree = lxet.parse('Input.xml')
data = []
inner = {}
for el in tree.xpath('/*/*'):
for i in el:
inner[i.tag] = i.text
data.append(inner)
inner = {}
df = pd.DataFrame(data)
def read_xml_lxml_xsl():
xml = lxet.parse('Input.xml')
xslstr = '''
<xsl:transform xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0">
<xsl:output version="1.0" encoding="UTF-8" indent="yes" method="text"/>
<xsl:strip-space elements="*"/>
<!-- HEADERS -->
<xsl:template match = "/*">
<xsl:for-each select="*[1]/*">
<xsl:value-of select="local-name()" />
<xsl:choose>
<xsl:when test="position() != last()">
<xsl:text>,</xsl:text>
</xsl:when>
<xsl:otherwise>
<xsl:text>
</xsl:text>
</xsl:otherwise>
</xsl:choose>
</xsl:for-each>
<xsl:apply-templates/>
</xsl:template>
<!-- DATA ROWS (COMMA-SEPARATED) -->
<xsl:template match="/*/*" priority="2">
<xsl:for-each select="*">
<xsl:if test="position() = 1">
<xsl:text>"</xsl:text>
</xsl:if>
<xsl:value-of select="." />
<xsl:choose>
<xsl:when test="position() != last()">
<xsl:text>","</xsl:text>
</xsl:when>
<xsl:otherwise>
<xsl:text>"
</xsl:text>
</xsl:otherwise>
</xsl:choose>
</xsl:for-each>
</xsl:template>
</xsl:transform>
'''
xsl = lxet.fromstring(xslstr)
transform = lxet.XSLT(xsl)
newdom = transform(xml)
df = pd.read_csv(StringIO(str(newdom)))
时序 （当前的XML和XML的子级是25倍（即900条StackOverflow用户记录）
# SHORTER FILE
python -mtimeit -s'import readxml_test_runs as test' 'test.read_xml_iterfind()'
100 loops, best of 3: 3.87 msec per loop
python -mtimeit -s'import readxml_test_runs as test' 'test.read_xml_iterparse()'
100 loops, best of 3: 5.5 msec per loop
python -mtimeit -s'import readxml_test_runs as test' 'test.read_xml_lxml_xpath()'
100 loops, best of 3: 3.86 msec per loop
python -mtimeit -s'import readxml_test_runs as test' 'test.read_xml_lxml_xsl()'
100 loops, best of 3: 5.68 msec per loop
# LARGER FILE
python -mtimeit -n'100' -s'import readxml_test_runs as test' 'test.read_xml_iterfind()'
100 loops, best of 3: 36 msec per loop
python -mtimeit -n'100' -s'import readxml_test_runs as test' 'test.read_xml_iterparse()'
100 loops, best of 3: 78.9 msec per loop
python -mtimeit -n'100' -s'import readxml_test_runs as test' 'test.read_xml_lxml_xpath()'
100 loops, best of 3: 32.7 msec per loop
python -mtimeit -n'100' -s'import readxml_test_runs as test' 'test.read_xml_lxml_xsl()'
100 loops, best of 3: 51.4 msec per loop
回答 0
性能：如何解释由于迭代解析文件而通常建议对较大文件使用的较慢iterparse？部分原因是由于if逻辑检查？
我认为更多的python代码会使它变慢，因为每次都会评估python代码。您是否尝试过像pypy这样的JIT编译器？
如果仅删除i并使用first_tag，它似乎会快很多，所以是的，部分原因在于if逻辑检查：
def read_xml_iterparse2(path):
data = []
inner = {}
first_tag = None
for (ev, el) in et.iterparse(path):
if not first_tag:
first_tag = el.tag
if el.tag == first_tag and len(inner) != 0:
data.append(inner)
inner = {}
if el.text is not None and len(el.text.strip()) > 0:
inner[el.tag] = el.text
df = pd.DataFrame(data)
%timeit read_xml_iterparse(path)
# 10 loops, best of 5: 33 ms per loop
%timeit read_xml_iterparse2(path)
# 10 loops, best of 5: 23 ms per loop
我不确定我是否了解上次if检查的目的，但也不确定为什么您会丢失仅空白元素。持续删除最后一个可以if节省一点时间：
def read_xml_iterparse3(path):
data = []
inner = {}
first_tag = None
for (ev, el) in et.iterparse(path):
if not first_tag:
first_tag = el.tag
if el.tag == first_tag and len(inner) != 0:
data.append(inner)
inner = {}
inner[el.tag] = el.text
df = pd.DataFrame(data)
%timeit read_xml_iterparse(path)
# 10 loops, best of 5: 34.4 ms per loop
%timeit read_xml_iterparse2(path)
# 10 loops, best of 5: 24.5 ms per loop
%timeit read_xml_iterparse3(path)
# 10 loops, best of 5: 20.9 ms per loop
现在，无论是否进行了这些性能改进，您的iterparse版本似乎都会产生一个更大的数据框。这似乎是一个有效的快速版本：
def read_xml_iterparse5(path):
data = []
inner = {}
for (ev, el) in et.iterparse(path):
# /ending parents trigger a new row, and in our case .text is \n followed by spaces. it would be more reliable to pass 'topusers' to our read_xml_iterparse5 as the .tag to check
if el.text and el.text[0] == '\n':
# ignore /stackoverflow
if inner:
data.append(inner)
inner = {}
else:
inner[el.tag] = el.text
return pd.DataFrame(data)
print(read_xml_iterfind(path).shape)
# (900, 8)
print(read_xml_iterparse(path).shape)
# (7050, 8)
print(read_xml_lxml_xpath(path).shape)
# (900, 8)
print(read_xml_lxml_xsl(path).shape)
# (900, 8)
print(read_xml_iterparse5(path).shape)
# (900, 8)
%timeit read_xml_iterparse5(path)
# 10 loops, best of 5: 20.6 ms per loop
内存：CPU内存是否与I / O调用中的时间相关？XSLT和XPath 1.0在较大的XML文档中往往无法很好地扩展，因为必须在内存中读取整个文件才能进行解析。
我不能完全确定“ I / O调用”是什么意思，但是如果您的文档足够小以适合缓存，那么一切都会更快，因为它不会从缓存中逐出其他项目。
策略：词典列表是否是Dataframe（）调用的最佳策略？请参阅以下有趣的答案：生成器版本和iterwalk用户定义的版本。两个上载列表到数据帧。
列表使用的内存较少，因此根据您拥有的列数，它可能会产生明显的不同。当然，这然后要求您的XML标记具有一致的顺序，看起来确实如此。该DataFrame()调用也将需要做的工作更少，因为它不必在每一行的dict中查找键，以弄清楚哪一列是什么值。