Using regex in xml etree parsing

Question

I need to parse xml file and find a values only starts with "123". How i can do this using this code below? It is possible to use regex inside this syntax?

import xml.etree.ElementTree as ET
parse = ET.parse('xml.xml')
print([ events.text for record in parse.findall('.configuration/system/') for events in record.findall('events')])

xml.xml

<rpc-reply>
 <configuration>
        <system>
            <preference>
                <events>123</events>
                <events>124</events>
                <events>1235</events>                    
            </preference>
        </system>
 </configuration>
</rpc-reply>

For regex, it would be probably the best to operate on un-parsed (string) xml - just get re.findall(r'>(123[^<]*)<', xml_string) - gets this: ['123', '1235']. Will get anything between > and < that starts with 123 and consists of any characters that are not < (because it should end the search, obviously). — h4z3
– h4z3, Commented Nov 7, 2019 at 8:06
@h4z3 yeah but, what if i only find those values inside <preference> tag or another? — Goroshek
– Goroshek, Commented Nov 7, 2019 at 8:17
Read about XPath use in ET.findall. XPath can do such filtering but you need to test what exactly you want. (Just play with it in the interactive console. I do that when I need something specific.) — h4z3
– h4z3, Commented Nov 7, 2019 at 8:24

har07 · Accepted Answer · 2019-11-07 09:51:55Z

XPath predicate can do that much using built-in function starts-with(). But you need to use library that fully support XPath 1.0 such as lxml:

from lxml import etree as ET
raw = '''<rpc-reply>
 <configuration>
        <system>
            <preference>
                <events>123</events>
                <events>124</events>
                <events>1235</events>                    
            </preference>
        </system>
 </configuration>
</rpc-reply>'''
root = ET.fromstring(raw)
query = 'configuration/system/preference/events[starts-with(.,"123")]'
print([events.text for events in root.xpath(query)])

If you still want to use regex, lxml supports regex despite XPath 1.0 specification does not include regex (see: Regex in lxml for python).

xml.etree only supports limited subset of XPath 1.0 expression, which does not include starts-with function (and definitely does not support regex). So you need to rely on python string function to check that:

....
query = 'configuration/system/preference/events'
print([events.text for events in root.findall(query) if events.text.startswith('123')])

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