How to update modify an XML file in python

Question

I have an XML document that I would like to update after it already contains data   I thought about opening the XML file in  a   append  mode  The problem is that the new data will be written after the root closing tag   How can I delete the last line of a file  then start writing data from that point  and then close the root tag   Of course I could read the whole file and do some string manipulations  but I don t think that s the best idea    Thanks for your time

User · Answer

Useful Python XML parsers    Minidom - functional but limited ElementTree - decent performance  more functionality lxml - high-performance in most cases  high functionality including real xpath support   Any of those is better than trying to update the XML file as strings of text   What that means to you   Open your file with an XML parser of your choice  find the node you re interested in  replace the value  serialize the file back out

User · Answer

As Edan Maor explained  the quick and dirty way to do it  for  utc-16  encoded  xml files   which you should not do for the resons Edam Maor explained  can done with the following python 2 7 code in case time constraints do not allow you to learn  propper  XML parses   Assuming you want to     Delete the last line in the original xml file   Add a line substitute a line Close the root tag    It worked in python 2 7 modifying an  xml file named  b xml  located in folder  a   where  a  was located in the  working folder  of python  It outputs the new modified file as  c xml  in folder  a   without yielding encoding errors  for me  in further use outside of python 2 7   pattern     lt Author gt   subst         lt Author gt     domain          user name     lt  Author gt   line index  0  set line count to 0 before starting file   io open  a b xml    r   encoding  utf-16   lines   file readlines   outFile   open  a c xml    w   for line in lines 0 len lines        line index  line index  1     if line index    len lines            1   amp  2  delete last line and adding another line in its place not writing it         outFile writelines  Write extra line here      n             4  Close root tag          outFile writelines   lt  phonebook gt      as in           http   tizag com xmlTutorial xmldocument php     else           3  Substitue a line if it finds the following substring in a line          pattern     lt Author gt           subst         lt Author gt     domain          user name     lt  Author gt           if pattern in line              line   subst             print line         outFile writelines line  just writing copying all the lines from the original xml except for the last

User · Answer

The quick and easy way  which you definitely should not do  see below   is to read the whole file into a list of strings using readlines    I write this in case the quick and easy solution is what you re looking for   Just open the file using open    then call the readlines   method  What you ll get is a list of all the strings in the file  Now  you can easily add strings before the last element  just add to the list one element before the last   Finally  you can write these back to the file using writelines     An example might help   my file   open filename   r   lines of file   my file readlines   lines of file insert -1   This line is added one before the last line   my file writelines lines of file    The reason you shouldn t be doing this is because  unless you are doing something very quick n  dirty  you should be using an XML parser  This is a library that allows you to work with XML intelligently  using concepts like DOM  trees  and nodes  This is not only the proper way to work with XML  it is also the standard way  making your code both more portable  and easier for other programmers to understand    Tim s answer mentioned checking out xml dom minidom for this purpose  which I think would be a great idea

User · Answer

While I agree with Tim and Oben Sonne that you should use an XML library  there are ways to still manipulate it as a simple string object     I likely would not try to use a single file pointer for what you are describing  and instead read the file into memory  edit it  then write it out    inFile   open  file xml    r   data   inFile readlines   inFile close     some manipulation on  data  outFile   open  file xml    w   outFile writelines data  outFile close

User · Answer

You should read the XML file using specific XML modules  That way you can edit the XML document in memory and rewrite your changed XML document into the file   Here is a quick start  http   docs python org library xml dom minidom html  There are a lot of other XML utilities  which one is best depends on the nature of your XML file and in which way you want to edit it

User · Answer

For the modification  you could use tag text from xml  Here is snippet  import xml etree ElementTree as ET  tree   ET parse  country data xml   root   tree getroot    for rank in root iter  rank        new rank   int rank text    1     rank text   str new rank       tree write  output xml    The rank in the code is example of tag  which depending on your XML file contents

User · Answer

What you really want to do is use an XML parser and append the new elements with the API provided   Then simply overwrite the file   The easiest to use would probably be a DOM parser like the one below   http   docs python org library xml dom minidom html

User · Answer

To make this process more robust  you could consider using the SAX parser  that way  you don t have to hold the whole file in memory   read  amp  write till the end of tree and then start appending

User · Answer

Using ElementTree   import xml etree ElementTree    Open original file et   xml etree ElementTree parse  file xml      Append new tag   lt a x  1  y  abc  gt body text lt  a gt  new tag   xml etree ElementTree SubElement et getroot     a   new tag text    body text  new tag attrib  x      1    must be str  cannot be an int new tag attrib  y      abc     Write back to file  et write  file xml   et write  file new xml     note  output written to file new xml for you to experiment  writing back to file xml will replace the old content   IMPORTANT  the ElementTree library stores attributes in a dict  as such  the order in which these attributes are listed in the xml text will NOT be preserved  Instead  they will be output in alphabetical order   also  comments are removed  I m finding this rather annoying   ie  the xml input text  lt b y  xxx  x  2  gt some body lt  b gt  will be output as  lt b x  2  y  xxx  gt some body lt  b gt  after alphabetising the order parameters are defined   This means when committing the original  and changed files to a revision control system  such as SVN  CSV  ClearCase  etc   a diff between the 2 files may not look pretty

[python] How to update/modify an XML file in python?

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