Python API

Main API

Using xmldiff from Python is very easy, you just import and call one of the three main API methods.

>>> from xmldiff import main
>>> main.diff_files("../tests/test_data/insert-node.left.html",
...                 "../tests/test_data/insert-node.right.html",
...                 diff_options={'F': 0.5, 'ratio_mode': 'fast'})
[UpdateTextIn(node='/body/div[1]', text=None),
 InsertNode(target='/body/div[1]', tag='p', position=0),
 UpdateTextIn(node='/body/div/p[1]', text='Simple text')]

Which one you choose depends on if the XML is contained in files, text strings or lxml trees.

• xmldiff.main.diff_files() takes as input paths to files, or file streams.
• xmldiff.main.diff_texts() takes as input Unicode strings.
• xmldiff.main.diff_trees() takes as input lxml trees.

The arguments to these functions are the same:

Parameters

left:

The “left”, “old” or “from” XML. The diff will show the changes to transform this XML to the “right” XML.

right:

The “right”, “new” or “target” XML.

diff_options:

A dictionary containing options that will be passed into the Differ():

F: A value between 0 and 1 that determines how similar two XML nodes must be to match as the same in both trees. Defaults to 0.5.

A higher value requires a smaller difference between two nodes for them to match. Set the value high, and you will see more nodes inserted and deleted instead of being updated. Set the value low, and you will get more updates insted of inserts and deletes.

uniqueattrs: A list of XML node attributes that will uniquely identify a node. See Unique Attributes for more info.

Defaults to ['{http://www.w3.org/XML/1998/namespace}id'].

ratio_mode:

The ratio_mode determines how accurately the similarity between two nodes is calculated. The choices are 'accurate', 'fast' and 'faster'. Defaults to 'fast'.

Using 'faster' often results in less optimal edits scripts, in other words, you will have more actions to achieve the same result. Using 'accurate' will be significantly slower, especially if your nodes have long texts or many attributes.

fast_match:

By default xmldiff will compare each node from one tree with all nodes from the other tree. It will then pick the one node that matches best as the match, if that match passes the match treshold F (see above).

If fast_match is true xmldiff will first make a faster run, trying to find chains of matching nodes, during which any match better than F will count. This significantly cuts down on the time to match nodes, but means that the matches are no longer the best match, only “good enough” matches.

formatter:

The formatter to use, see Using Formatters. If no formatter is specified the function will return a list of edit actions, see The Edit Script.

Result

If no formatter is specified the diff functions will return a list of actions. Such a list is called an Edit Script and contains all changes needed to transform the “left” XML into the “right” XML.

If a formatter is specified that formatter determines the result. The included formatters, diff, xml, and old all return a Unicode string.

xmldiff is still under rapid development, and no guarantees are done that the output of one version will be the same as the output of any previous version. The actions of the edit script can be in a different order or replaced by equivalent actions dependingon the version of xmldiff, but if the Edit Script does not correctly transform one XML tree into another, thas is regarded as a bug. This means that the output of the xml format also may change from version to version. There is no “correct” solution to how that output should look, as the same change can be represented in several different ways.

Unique Attributes

The uniqueattrs argument is a list of strings specifying attributes that uniquely identify a node in the document. This is used by the differ when trying to match nodes. If one node in the left tree has a this attribute, the node in the right three with the same value for that attribute will match, regardless of other attributes, child nodes or text content.

The default is ['{http://www.w3.org/XML/1998/namespace}id'], which is the xml:id attribute. But if your document have other unique identifiers, you can pass them in instead. If you for some reason do not want the differ to look at the xml:id attribute, pass in an empty list.

Using Formatters

By default the diff functions will return an edit script, but if you pass in a formatter the result will be whatever that formatter returns.

The three included formatters, diff, xml and old, all return Unicode strings. The diff formatter will return a string with the edit script printed out, one action per line. Each line is enclosed in brackets and consists of a string describing the action, and the actions arguments. This is the output format of xmldiff 0.6/1.x, however, the actions and arguments are not the same, so the output is not compatible.

>>> from xmldiff import formatting
>>> formatter = formatting.DiffFormatter()
>>> print(main.diff_files("../tests/test_data/insert-node.left.html",
...                       "../tests/test_data/insert-node.right.html",
...                       formatter=formatter))
[update-text, /body/div[1], null]
[insert, /body/div[1], p, 0]
[update-text, /body/div/p[1], "Simple text"]

The other two differs return XML with tags describing the changes. These formats are designed so they easily can be changed into something that will render nicely, for example with XSLT replacing the tags with the format you need.

>>> from xmldiff import formatting
>>> formatter = formatting.XMLFormatter(normalize=formatting.WS_BOTH)
>>> print(main.diff_files("../tests/test_data/insert-node.left.html",
...                       "../tests/test_data/insert-node.right.html",
...                       formatter=formatter))
<body xmlns:diff="http://namespaces.shoobx.com/diff">
  <div id="id">
    <p diff:insert="">Simple text</p>
  </div>
</body>

The Edit Script

The default result of the diffing methods is to return an edit script, which is a list of Python objects called edit actions. Those actions tell you how to turn the “left” tree into the “right” tree.

xmldiff has nine different actions. These specify one or two nodes in the XML tree, called node or target. They are specified with an XPATH expression that will uniquely identify the node.

The other arguments vary depending on the action.

InsertNode(target, tag, position)

The InsertNode action means that the node specified in target needs a new subnode. tag specifies which tag that node should have. The position argument specifies which position the new node should have, 0 means that the new node will be inserted as the first child of the target. Note that this is different from XPATH, where the first node is 1. This is for ease of use, since Python is zero-indexed.

Example:

>>> left = '<document><node>Content</node></document>'
>>> right = '<document><node>Content</node><newnode/></document>'
>>> main.diff_texts(left, right)
[InsertNode(target='/document[1]', tag='newnode', position=1)]

DeleteNode(node)

The DeleteNode action means that the node specified in node should be deleted.

Example:

>>> left = '<document><node>Content</node></document>'
>>> right = '<document/>'
>>> main.diff_texts(left, right)
[DeleteNode(node='/document/node[1]')]

MoveNode(node, target, position)

The MoveNode action means that the node specified in node should be moved to be a child under the target node. The position argument specifies which position it should have, 0 means that the new node will be inserted as the first child of the target. Note that this is different from XPATH, where the first node is 1. This is for ease of use, since Python is zero-indexed.

If the move is within the same parent, the position can be ambiguous. If you have a child that is in position 1, but should be moved to position 3, that position does not include the node being moved, but signifies the position the node should end up at after the move. When implementing a MoveNode() it is therefore easiest to remove the node from the parent first, and then insert it at the given position.

Example:

>>> left = '<document><node>Content</node><movenode/></document>'
>>> right = '<document><movenode/><node>Content</node></document>'
>>> main.diff_texts(left, right)
[MoveNode(node='/document/node[1]', target='/document[1]',
          position=1)]

InsertAttrib(node, name, value)

The InsertAttrib action means that the node specified in node should get a new attribute. The name `` and ``value arguments specify the name and value of that attribute.

Example:

>>> left = '<document><node/></document>'
>>> right = '<document newattr="newvalue"><node/></document>'
>>> main.diff_texts(left, right)
[InsertAttrib(node='/document[1]', name='newattr',
              value='newvalue')]

DeleteAttrib(node, name)

The DeleteAttrib action means that an attribute of the node specified in target should be deleted. The name argument specify which attribute.

Example:

>>> left = '<document newattr="newvalue"><node/></document>'
>>> right = '<document><node/></document>'
>>> main.diff_texts(left, right)
[DeleteAttrib(node='/document[1]', name='newattr')]

RenameAttrib(node, name)

The RenameAttrib action means that an attribute of the node specified in node should be renamed. The oldname and newname arguments specify which attribute and it’s new name.

Example:

>>> left = '<document attrib="value"><node/></document>'
>>> right = '<document newattrib="value"><node/></document>'
>>> main.diff_texts(left, right)
[RenameAttrib(node='/document[1]', oldname='attrib',
              newname='newattrib')]

UpdateAttrib(node, name)

The UpdateAttrib action means that an attribute of the node specified in node should get a new value. The name and value arguments specify which attribute and it’s new value.

Example:

>>> left = '<document attrib="value"><node/></document>'
>>> right = '<document attrib="newvalue"><node/></document>'
>>> main.diff_texts(left, right)
[UpdateAttrib(node='/document[1]', name='attrib', value='newvalue')]

UpdateTextIn(node, name)

The UpdateTextIn action means that an text content of the node specified in node should get a new value. The text argument specify the new value of that text.

Example:

>>> left = '<document><node>Content</node></document>'
>>> right = '<document><node>New Content</node></document>'
>>> main.diff_texts(left, right)
[UpdateTextIn(node='/document/node[1]', text='New Content')]

UpdateTextAfter(node, name)

The UpdateTextAfter action means that an text that trails the node specified in node should get a new value. The text argument specify the new value of that text.

Example:

>>> left = '<document><node>Content</node></document>'
>>> right = '<document><node>Content</node>Trailing text</document>'
>>> main.diff_texts(left, right)
[UpdateTextAfter(node='/document/node[1]', text='Trailing text')]

InsertComment(target, position, text)

Since comments doesn’t have a tag, the normal InsertNode() action doesn’t work nicely with a comment. Therefore comments get their own insert action. Just like InsertNode() it takes a target node and a position. It naturally has no tag but instead has a text argument, as all comments have text and nothing else.

UpdateTextIn() and DeleteNode() works as normal for comments.

Example:

>>> left = '<document><node>Content</node></document>'
>>> right = '<document><!-- A comment --><node>Content</node></document>'
>>> main.diff_texts(left, right)
[InsertComment(target='/document[1]', position=0, text=' A comment ')]