python - 如何使用 Python 解析来自欧洲中央银行的 XML 文件

Question

我正在尝试用欧元汇率解析来自欧洲中央银行的 XML 文件。不幸的是，我在解析 XML 文件时遇到了困难。当我删除困难的部分(与“gesmes”相关的所有内容)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。我为此使用了 ElementTree API。

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货币(根据用户输入)并取回汇率，以便我可以使用结果。

Answer 1

您有一个带命名空间的 XML 文件。 ElementTree 在命名空间方面不太聪明。您需要提供 .find() , findall()和 iterfind()方法显式命名空间字典。这没有很好地记录:

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； './/' 表示查找任何子标签，ex:Cube将搜索限制为 <Cube>命名空间中标有 ex 的标签前缀(来自 namespaces 映射)和 [@currency]将搜索限制为具有 currency 的元素属性。

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费率；要么构建字典，要么直接在 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']))