Python – How to parse XML file from European Central Bank with Python

elementtreepythonpython-3.xxml

I am trying to parse an XML file from the European Central Bank with the Euro rates.
Unfortunatly I get stuck with parsing the XML file. When I remove the difficult part (everything related with "gesmes") I have no problem iterating through the "Cube" elements but I am not able to deal with the "gesmes" part of the xml file.
I used the ElementTree API for this.

Sample XML file: 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>

What I want is to search for a specific currency (from users input) and get the rate back so I can use the result.

Best Answer

You have a namespaced XML file. ElementTree is not too smart about namespaces. You need to give the .find(), findall() and iterfind() methods an explicit namespace dictionary. This is not documented very well:

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'])

This uses a simple XPath query; './/' means find any child tag, ex:Cube limits the search to the <Cube> tags in the namespace labeled with the ex prefix (from the namespaces mapping) and [@currency] limits the search to elements that have a currency attribute.

Demo:

>>> 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

You can use this information to search for the specific rate too; either build a dictionary, or search the XML document directly for matching currencies:

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']))

Related Solutions

Python – How to execute a program or call a system command

Use the subprocess module in the standard library:

import subprocess
subprocess.run(["ls", "-l"])

The advantage of subprocess.run over os.system is that it is more flexible (you can get the stdout, stderr, the "real" status code, better error handling, etc...).

Even the documentation for os.system recommends using subprocess instead:

The subprocess module provides more powerful facilities for spawning new processes and retrieving their results; using that module is preferable to using this function. See the Replacing Older Functions with the subprocess Module section in the subprocess documentation for some helpful recipes.

On Python 3.4 and earlier, use subprocess.call instead of .run:

subprocess.call(["ls", "-l"])

Python – How to parse XML and count instances of a particular node attribute

I suggest ElementTree. There are other compatible implementations of the same API, such as lxml, and cElementTree in the Python standard library itself; but, in this context, what they chiefly add is even more speed -- the ease of programming part depends on the API, which ElementTree defines.

First build an Element instance root from the XML, e.g. with the XML function, or by parsing a file with something like:

import xml.etree.ElementTree as ET
root = ET.parse('thefile.xml').getroot()

Or any of the many other ways shown at ElementTree. Then do something like:

for type_tag in root.findall('bar/type'):
    value = type_tag.get('foobar')
    print(value)

And similar, usually pretty simple, code patterns.

Best Answer

Related Solutions

Python – How to execute a program or call a system command

Python – How to parse XML and count instances of a particular node attribute

Related Topic