Whatever your XML string is, you can write it to the file of your choice by opening a file for writing and writing the string to the file.

from xml.dom import minidom

xmlstr = minidom.parseString(ET.tostring(root)).toprettyxml(indent="   ")
with open("New_Database.xml", "w") as f:
    f.write(xmlstr)

There is one possible complication, especially in Python 2, which is both less strict and less sophisticated about Unicode characters in strings. If your toprettyxml method hands back a Unicode string (u"something"), then you may want to cast it to a suitable file encoding, such as UTF-8. E.g. replace the one write line with:

f.write(xmlstr.encode('utf-8'))

You could use the library lxml (Note top level link is now spam) , which is a superset of ElementTree. Its tostring() method includes a parameter pretty_print - for example:

>>> print(etree.tostring(root, pretty_print=True))
<root>
  <child1/>
  <child2/>
  <child3/>
</root>

As the docs say, in the write method:

file is a file name, or a file object opened for writing.

This includes a StringIO object. So:

outfile = cStringIO.StringIO()
tree.write(of)

Then you can just pretty-print outfile using your favorite method—just outfile.seek(0) then pass outfile itself to a function that takes a file, or pass outfile.getvalue() to a function that takes a string.

However, notice that many of the ways to pretty-print XML in the question you linked don't even need this. For example:

• lxml.etree.tostring (answer #2): lxml.etree is a near-perfect superset of the stdlib etree, so if you're going to use it for pretty-printing, just use it to build the XML in the first place.
• Effbot indent/prettyprint (answer #3): This expects an ElementTree tree, which is exactly what you already have, not a string or file.

lxml is recent, updated, and includes a pretty print function

import lxml.etree as etree

x = etree.parse("filename")
print etree.tostring(x, pretty_print=True)

Check out the lxml tutorial: https://lxml.de/tutorial.html

Have you looked at this post within StackOverflow? I think it covers what you want:

in-place prettyprint formatter

def indent(elem, level=0):
    i = "\n" + level*"  "
    if len(elem):
        if not elem.text or not elem.text.strip():
            elem.text = i + "  "
        if not elem.tail or not elem.tail.strip():
            elem.tail = i
        for elem in elem:
            indent(elem, level+1)
        if not elem.tail or not elem.tail.strip():
            elem.tail = i
    else:
        if level and (not elem.tail or not elem.tail.strip()):
            elem.tail = i

That sample code was from the post and from effbot.org

Also, for additional information, you're not calling the tostring() method properly. Have a look at Python's website for more information.