Python’s xml.dom.minidom.toprettyxml has a feature\/flaw that renders it useless for many common applications.
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Someone was kind enough to post a hack which works around the problem. That hack had a small bug, which I’ve fixed; you’ll find the revised code below.<\/span><\/p>\n UPDATED<\/span> Forget the hack; I’ve found another, better solution. See below<\/a>. And please leave a comment<\/a> if you find these workarounds helpful, or if you come across a better solution.<\/p>\n METAUPDATE<\/span> Since writing this post, I’ve started using lxml<\/a> for all my xml processing Python. Incidentally, it fixes the pretty printing problem with toprettyxml, but the actual reason I switched was for performance: lxml parses xml significantly faster (an order of magnitude faster) than minidom. So my new recommendation is: consider using lxml instead of minidom.<\/p>\n First, a short summary of the problem. (Other descriptions can be found here<\/a> and here<\/a>.) Feel free to jump ahead to all the workarounds<\/a>, or straight to my solution of choice<\/a>.<\/p>\n toprettyxml adds extra white space<\/strong> when printing the contents of text nodes. This may not sound like a serious drawback, but it is. Consider a simple xml snippet:<\/p>\n This Python script:<\/p>\n generates this output:<\/p>\n Note the extra line breaks: the text “Ron Rothman” is printed on its own line, and indented. That may not matter much to a human reading the output, but it sure as hell matters to an XML parser. (Recall: whitespace is significant<\/em> <\/a> in XML)<\/p>\n To put it another way: the DOM object that represents the output (with line breaks) is NOT identical to the DOM object that represented the input.<\/p>\n Semantically, the author in the original XML is This is devastating news to anyone who hopes to re-parse the “pretty” XML in some other context. It means that you can’t use minidom.toprettyxml() to produce XML that will be parsed downstream<\/strong>.<\/p>\n <\/a><\/p>\n UPDATED<\/span> If you’re in a rush, skip ahead to the best solution<\/a>, #4.<\/p>\n There are plenty of other XML packages to choose from. Use minidom.toxml(), which doesn’t suffer from the same problem (because it doesn’t insert any whitespace). Replace toprettyxml by using the code below. I just copied the original toprettyxml code from [Credit to Oluseyi at gamedev.net<\/a> for the original hack; I just fixed it so that it worked with character entities.]<\/p>\n <\/a><\/p>\nThe Problem<\/h3>\n
<Author>Ron Rothman<\/Author>\n<\/pre>\n
# python 2.4<\/span>\nimport xml.dom.minidom as dom\nmyText = '''<Author>Ron Rothman<\/Author>'''\nprint xml.dom.minidom.parseString(myText).toprettyxml()\n<\/pre>\n<?xml version=\"1.0\" ?><\/span>\n<Author>\n Ron Rothman\n<\/Author>\n<\/pre>\n\"Ron Rothman\"<\/code>, but the author in the “pretty” XML is [approximately] \" Ron Rothman \"<\/code>.<\/p>\nWorkarounds<\/h3>\n
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1. Don’t use minidom<\/h4>\n
\nBut<\/strong>: minidom is appealing because it’s lightweight, and is included with the Python distribution. Seems a shame to toss it for just one flaw.
\nUPDATE<\/span>I’ve started using lxml<\/a> and I highly recommend it as a replacement for minidom or PyXML.<\/p>\n2. Use minidom, but don’t use toprettyxml()<\/h4>\n
\nBut<\/strong>: Your machine-readable XML will make heads spin, should someone be foolish enough to try to read it.<\/p>\n3. Hack toprettyxml to do The Right Thing<\/h4>\n
\nBut<\/strong>: It smells. Like a hack. Fragile; likely to break with future releases of minidom.
\nOn the other hand: It’s not that<\/em> bad. And hey, it does the trick. (But YMMV.)<\/p>\ndef fixed_writexml(self, writer, indent=\"\", addindent=\"\", newl=\"\"):\n # indent = current indentation\n # addindent = indentation to add to higher levels\n # newl = newline string\n writer.write(indent+\"<\" + self.tagName)\n\n attrs = self._get_attributes()\n a_names = attrs.keys()\n a_names.sort()\n\n for a_name in a_names:\n writer.write(\" %s=\\\"\" % a_name)\n xml.dom.minidom.<\/span>_write_data(writer, attrs[a_name].value)\n writer.write(\"\\\"\")\n if self.childNodes:\n if len(self.childNodes) == 1 \\\n and self.childNodes[0].nodeType == xml.dom.minidom.Node.TEXT_NODE:\n writer.write(\">\")\n self.childNodes[0].writexml(writer, \"\", \"\", \"\")\n writer.write(\"<\/%s>%s\" % (self.tagName, newl))\n return<\/span>\n writer.write(\">%s\"%(newl))\n for node in self.childNodes:\n node.writexml(writer,indent+addindent,addindent,newl)\n writer.write(\"%s<\/%s>%s\" % (indent,self.tagName,newl))\n else:\n writer.write(\"\/>%s\"%(newl))\n# replace minidom's function with ours\nxml.dom.minidom.Element.writexml = fixed_writexml<\/span>\n<\/pre>\n\/usr\/lib\/python2.4\/xml\/dom\/minidom.py<\/code> and made the modifications that are highlighted in yellow<\/span>. It ain’t pretty, but it seems to work. (Suggestions for improvements (I’m a Python n00b) are welcome.)<\/p>\nUPDATE!<\/span> 4. Use xml.dom.ext.PrettyPrint<\/h4>\n