如何用Python解析欧洲央行的XML文件

Question

我正在尝试解析来自欧洲中央银行的带有欧元汇率的XML文件。不幸的是，我不得不解析XML文件。当我删除困难的部分(所有与"gesmes“相关的部分)时，我可以毫无问题地遍历"Cube”元素，但我无法处理xml文件的“gesmes”部分。为此，我使用了ElementTree应用编程接口。

示例XML文件：http://www.ecb.int/stats/eurofxref/eurofxref-daily.xml

<?xml version="1.0" encoding="UTF-8"?>
<gesmes:Envelope xmlns:gesmes="http://www.gesmes.org/xml/2002-08-01" xmlns="http://www.ecb.int/vocabulary/2002-08-01/eurofxref">
    <gesmes:subject>Reference rates</gesmes:subject>
    <gesmes:Sender>
        <gesmes:name>European Central Bank</gesmes:name>
    </gesmes:Sender>
    <Cube>
        <Cube time='2013-06-21'>
            <Cube currency='USD' rate='1.3180'/>
            <Cube currency='JPY' rate='128.66'/>
            <Cube currency='BGN' rate='1.9558'/>
            <Cube currency='CZK' rate='25.825'/>
            <Cube currency='DKK' rate='7.4582'/>
            <Cube currency='GBP' rate='0.85330'/>
            <Cube currency='HUF' rate='298.87'/>
            <Cube currency='LTL' rate='3.4528'/>
            <Cube currency='LVL' rate='0.7016'/>
            <Cube currency='PLN' rate='4.3289'/>
            <Cube currency='RON' rate='4.5350'/>
            <Cube currency='SEK' rate='8.6927'/>
            <Cube currency='CHF' rate='1.2257'/>
            <Cube currency='NOK' rate='7.9090'/>
            <Cube currency='HRK' rate='7.4905'/>
            <Cube currency='RUB' rate='43.2260'/>
            <Cube currency='TRY' rate='2.5515'/>
            <Cube currency='AUD' rate='1.4296'/>
            <Cube currency='BRL' rate='2.9737'/>
            <Cube currency='CAD' rate='1.3705'/>
            <Cube currency='CNY' rate='8.0832'/>
            <Cube currency='HKD' rate='10.2239'/>
            <Cube currency='IDR' rate='13088.24'/>
            <Cube currency='ILS' rate='4.7891'/>
            <Cube currency='INR' rate='78.1200'/>
            <Cube currency='KRW' rate='1521.52'/>
            <Cube currency='MXN' rate='17.5558'/>
            <Cube currency='MYR' rate='4.2222'/>
            <Cube currency='NZD' rate='1.7004'/>
            <Cube currency='PHP' rate='57.707'/>
            <Cube currency='SGD' rate='1.6790'/>
            <Cube currency='THB' rate='41.003'/>
            <Cube currency='ZAR' rate='13.4906'/>
        </Cube>
    </Cube>
</gesmes:Envelope>

我想要的是搜索特定的货币(从用户输入)，并获得汇率，以便我可以使用结果。

Answer 1

您有一个命名空间的XML文件。ElementTree在名称空间方面并不是很聪明。您需要为.find()、findall()和iterfind()方法提供一个明确的名称空间字典。这并没有很好地记录下来：

namespaces = {'ex': 'http://www.ecb.int/vocabulary/2002-08-01/eurofxref'} # add more as needed

for cube in root.findall('.//ex:Cube[@currency]', namespaces=namespaces):
    print(cube.attrib['currency'], cube.attrib['rate'])

这使用了一个简单的XPath查询；'.//‘表示查找任何子标记，ex:Cube将搜索限制为使用ex前缀标记的名称空间中的<Cube>标记(来自namespaces映射)，而[@currency]将搜索限制为具有currency属性的元素。

演示：

>>> import requests
>>> r = requests.get('http://www.ecb.int/stats/eurofxref/eurofxref-daily.xml', stream=True)
>>> from xml.etree import ElementTree as ET
>>> tree = ET.parse(r.raw)
>>> root = tree.getroot()
>>> namespaces = {'ex': 'http://www.ecb.int/vocabulary/2002-08-01/eurofxref'}
>>> for cube in root.findall('.//ex:Cube[@currency]', namespaces=namespaces):
...     print(cube.attrib['currency'], cube.attrib['rate'])
... 
USD 1.3180
JPY 128.66
BGN 1.9558
CZK 25.825
DKK 7.4582
GBP 0.85330
HUF 298.87
LTL 3.4528
LVL 0.7016
PLN 4.3289
RON 4.5350
SEK 8.6927
CHF 1.2257
NOK 7.9090
HRK 7.4905
RUB 43.2260
TRY 2.5515
AUD 1.4296
BRL 2.9737
CAD 1.3705
CNY 8.0832
HKD 10.2239
IDR 13088.24
ILS 4.7891
INR 78.1200
KRW 1521.52
MXN 17.5558
MYR 4.2222
NZD 1.7004
PHP 57.707
SGD 1.6790
THB 41.003
ZAR 13.4906

您也可以使用此信息来搜索特定的汇率；或者构建一个字典，或者直接在XML文档中搜索匹配的货币：

currency = input('What currency are you looking for? ')
match = root.find('.//ex:Cube[@currency="{}"]'.format(currency.upper()), namespaces=namespaces)
if match is not None:
    print('The rate for {} is {}'.format(currency, match.attrib['rate']))

Answer 2

你也可以这样做：

from xml.etree import cElementTree as ET
full_file = 'eurofxref-daily.xml'    # has to be full path
tree = ET.ElementTree(file=full_file)
root = tree.getroot()

for child in root:
    for subchild in child:
        for subsubchild in subchild:
            print(subsubchild.attrib['currency'])
            print(subsubchild.attrib['rate'])