非贪婪 XML 中的多个匹配项（Python 正则表达式）

Question

I know this topic is asked a lot but I couldn't find an answer to my question:

In the attached image there are many different buffers, and I wish to match only the buffers that have "Lut" in their names (notice there are 2 matches in the string in the image). The problem I have is that the matches contain also the buffers that come before the one I want.

I'm pretty new to regex and still trying to learn as much so any explanation will be appreciated.

Thank you! :)

The string is attached for you comfort (if needed):

<?xml version="1.0" encoding="utf-8"?>
<pimp xmlns:dt="urn:schemas-microsoft-com:datatypes">
    <dllPath>C:\ReplayCode\Apps\Pimp</dllPath>
    <buffers>   
    <buffer name="InputMask">
            <width>5120</width>
            <height>3072</height>
            <data>UCHAR</data>
            <channels>1</channels>
            <type>IMG</type>
    </buffer>
    <buffer name="MaskErode">
            <width>5120</width>
            <height>3072</height>
            <data>UCHAR</data>
            <channels>1</channels>
            <type>IMG</type>
    </buffer>
    <buffer name="BlablaLutBla">
            <width>256</width>
            <height>256</height>
            <data>UCHAR</data>
            <channels>1</channels>
            <type>IMG</type>
    </buffer>
    <buffer name="MaskClose">
            <width>5120</width>
            <height>3072</height>
            <data>UCHAR</data>
            <channels>1</channels>
            <type>IMG</type>
    </buffer>
    <buffer name="InputVis">
            <width>5120</width>
            <height>3072</height>
            <data>UCHAR</data>
            <channels>3</channels>
            <type>IMG</type>
    </buffer>   
        <buffer name="AddMaskEdge">
            <width>5120</width>
            <height>3072</height>
            <data>UCHAR</data>
            <channels>1</channels>
            <type>IMG</type>
    </buffer>
    <buffer name="EdgeVis">
            <width>5120</width>
            <height>3072</height>
            <data>UCHAR</data>
            <channels>3</channels>
            <type>IMG</type>
    </buffer>       
        <buffer name="GrayEdge">
            <width>5120</width>
            <height>3072</height>
            <data>UCHAR</data>
            <channels>1</channels>
            <type>IMG</type>
    </buffer>
    <buffer name="EdgeMaskMulThreshold">
            <width>5120</width>
            <height>3072</height>
            <data>UCHAR</data>
            <channels>1</channels>
            <type>IMG</type>
    </buffer>
    <buffer name="MaskMulEdge">
            <width>5120</width>
            <height>3072</height>
            <data>UCHAR</data>
            <channels>1</channels>
            <type>IMG</type>
    </buffer>   
    </buffers>  

The regex I tried is this:

<buffer name=".*?Lut.*?">.*?<\/buffer>

And I expected 2 matches:

<buffer name="BlablaLutBla">
            <width>256</width>
            <height>256</height>
            <data>UCHAR</data>
            <channels>1</channels>
            <type>IMG</type>
    </buffer>

and

<buffer name="2ndLutBlabla">
            <width>256</width>
            <height>256</height>
            <data>UCHAR</data>
            <channels>1</channels>
            <type>IMG</type>
    </buffer>

Answer 1

You can use BeautifulSoup to parse your tag.

import re
from bs4 import BeautifulSoup

input_xml = ''' some xml '''
soup = BeautifulSoup(input_xml, "lxml-xml")
print soup.find_all('buffer', attrs={"name": re.compile('Lut')})

If you do not have this installed already:

pip install beautifulsoup4
pip install lxml

Answer 2

Since you need to manipulate the data inside an XML document, use an XML parser. An answer above already shows how to instantiate the XML tree, but does not dwell upon the structure modification.

BTW, if you instantiate the XML from a string, use ET.fromstring

import xml.etree.ElementTree as ET
...
xml = "<<YOUR XML STRING>>" 
root = ET.fromstring(xml)

Else, when reading from a file:

tree = ET.parse('file.xml')
root = tree.getroot()

Then, you can use the following replacements (where you can actually use a regex if necessary, because here you will already have to deal with plain, unmarked up text data):

for buffer in root.findall("buffers/buffer"): 
    if "Lut" in buffer.get("name"):
        buffer.find('width').text = "100"    # Set inner text of buffer child named 'width'
        buffer[1].text = "125"               # Set the 2nd child inner text
        buffer.set('type', 'MY_TYPE');       # Add an attribute to buffer

You can print the updated XML using .dump() :

print ET.dump(root)                          # Print updated XML

Or write an updated DOM to the file (if you are working with a file):

tree.write('output.xml')

See IDEONE demo showing modifications on an XML string.

Answer 3

You might want to use xml parsing in python instead, it is quite easy:

import xml.etree.ElementTree as ET
tree = ET.parse(xml)
for buffer in tree.findall("buffers/buffer"): 
    if "Lut" in buffer.get("name"):
        # do your stuff
        pass

Answer 4

<buffer name="[^"]*Lut[^"]*">.*?<\/buffer>

See Demo

In your regex's <buffer name=".*?Lut , it will match from the first <buffer to the first Lut .( non-greedy worked.If greedy,it will match the last Lut )