The following example shows how to create a binding from an XBEL file (a popular XML format for bookmarks that was developed by Python's very own XML-SIG). There is a sample XBEL file you can use in the demo directory.

        doc = amara.parse('xbel.xml')
      

The following sample code prints the first and second bookmark titles:

        print doc.xbel.folder.bookmark.title
print doc.xbel.folder.bookmark[1].title
      

Note that Bindery tries to make things as natural as possible. You can access child elements by just using their name, usually. If there is more than one with the same name it grabs the first one. You can use list indices to specify one of multiple child elements with the same name. Naturally, a more explicit way of getting the first bookmark's title is:

        print doc.xbel.folder.bookmark[0].title
      

title is an element containing only text. the expression doc.xbel.folder.bookmark[0].title returns the binding object representing the element. Such objects have unicode conversion methods so that you can get their descendant text (all text nodes in the element's subtree), which is printed in the above line. The following four lines are all equivalent:

print doc.xbel.folder.bookmark.title
print doc.xbel.folder.bookmark[0].title
print unicode(doc.xbel.folder.bookmark.title)
print unicode(doc.xbel.folder.bookmark[0].title)
      

Calling the unicode conversion on an element node in Amara is very similar to calling the string conversion on an element node in XPath.

The following snippet is a recursive function that prints out all bookmark URLs in the file:

def all_titles_in_folder(folder):
    #Warning: folder.bookmark will raise an AttributeError if there are no bookmarks
    for bookmark in folder.bookmark:
        print bookmark.href
    if hasattr(folder, "folder"):
        #There are sub-folders
        for folder in folder.folder:
            all_titles_in_folder(folder)
    return

for folder in doc.xbel.folder:
    all_titles_in_folder(folder)
      

You would probably not do this in actual usage, though. You can perform this task with much less code, without recursion, and with a speed boost using XPath, which is covered in a later section.

If you want to count the number of elements of the same name, use len.

        len(doc.xbel.folder)
      

This gives the number of top-level folders.

In the default binding XML elements turn into specialized objects. For each generic identifier (element name) a class is generated that is derived from bindery.element_base. Attributes become simple data members whose value is a Unicode object containing the attribute value.

Element objects are specially constructed so they can be treated as single objects (in which case the first child element of the corresponding name is selected, or one can use list item access notation or even iterate.

Going back to the example, binding.xbel.folder.bookmark is the same as binding.xbel.folder.bookmark[0]. Both return the first bookmark in the first folder. To get the second bookmark in the first folder, use binding.xbel.folder.bookmark[1].

Bindery by default preserves ordering information from the source XML. You can access this through the children list of element and document objects:

        folder.xml_children
      

Within the children list, child elements are represented using the corresponding binding objects, child text becomes simple Unicode objects. Notice that in the default binding text children are normalized, meaning that the binding will never place two text nodes next to each other in xml_children.

If an element node contains text as well as child elements, be aware of the how descendant text nodes are accessed. You can get the accumulated text children of an element using the xml_child_text property. Given the document <a>1<b>2</b>3<c/></a>, a.xml_child_text would return u'13'. On the other hand, converting to Unicode (unicode(a)) would return u'123'.

You can get some information about the structure of most bindery objects by calling the xml_doc method.

>>> import amara
>>> doc = amara.parse('monty.xml')
>>> print doc.xml_doc()
Object references based on XML child elements:
monty (1 element) based on 'monty' in XML
>>> print doc.monty.xml_doc()
Object references based on XML child elements:
python (2 elements) based on 'python' in XML
>>> print doc.monty.python.xml_doc()
Object references based on XML attributes:
spam based on 'spam' in XML
Object references based on XML child elements:
>>> print doc.monty.python.spam
eggs
      

This is human-readable material, for convenience, but you can also get node structure information in machine-readable form. xml_properties returns a dictionary whose keys represent the object reference names from the XML attributes and elements.

>>> import amara
>>> doc = amara.parse("<a x='1'>hello<b/>lovely<c/>world</a>")
>>> doc.a.xml_properties
{u'x': u'1', u'c': &lt;amara.bindery.c object at 0xb7bbcdcc>, u'b': &lt;amara.bindery.b object at 0xb7bbcb8c>}
      

xml_child_elements returns similar dictionary, but reduced to only the child element.

>>> #Continuing from the above snippet
>>> doc.a.xml_child_elements
      

{u'c': <amara.bindery.c object at 0xb7bbcdcc>, u'b': <amara.bindery.b object at 0xb7bbcb8c>}

The preservation of ordering information means that Bindery does a pretty good job of allowing you to render binding objects back to XML form. Use the xml method for this.

        print doc.xml()
      

The xml method returns encoded text, not Unicode. The default encoding is UTF-8. You can also serialize a portion of the document.

        print doc.xbel.folder.xml() #Just the first folder
      

You can pass in a stream for the output:

        doc.xml(sys.stdout)
      

You can control such matters as the output encoding, whether the output is pretty-printed, whether there is an output XML declaration, etc. by using parameters that control the output, based on the XSLT output control attributes. As an example, if you pas in omitXmlDeclaration=u"yes" the output of the XML declaration is suppressed. Here are the other parameters you can set.

• encoding - the character encoding to use (default UTF-8). The writer will automatically use character entities where necessary.

• omitXmlDeclaration - "yes" to suppress output of the XML declaration. Default "no".

• standalone - "yes" to set standalone in the XML declaration.

• mediaType - sets the media type of the output. You'll probably never need this.

• cdataSectionElements - a list of element names whose output will be wrapped in a CDATA section. This can provide for friendlier output in some cases.

Bindery supports an XPath subset that covers almost all of that standard. The XPath features that are not supported are very rare, and for pracctical purposes you can assume it's complete XPath support. The folowing example retrieves all top-level folders:

        tl_folders = doc.xbel.xml_xpath(u'folder')
for folder in tl_folders:
    print folder.title
      

You invoke the xml_xpath method on the object you wish to serve as the context for the XPath query. To get the first element child (regardless of node name) of the first bookmark of the first folder, use:

        doc.xbel.folder.bookmark.xml_xpath(u'*[1]')
      

or

        doc.xbel.xml_xpath(u'folder[1]/bookmark[1]/*[1]')
      

or

        doc.xbel.xml_xpath(u'/folder[1]/bookmark[1]/*[1]')
      

or

        doc.xml_xpath(u'xbel/folder[1]/bookmark[1]/*[1]')
      

etc.

Warning: in Python, lists indices start with 0 while they start with 1 in XPath.

Notice: this XPath returns a node set, rendered in Python as a list of nodes. It happens to be a list of one node, but you still have to extract it with [0].

The return value depends on the XPath expression (expr)

• If expr reults in an XPath string, the return value is a Python Unicode object

• If expr reults in an XPath number, the return value is a Python float

• If expr reults in an XPath boolean, the return value is a Python bool object

• If expr reults in an XPath node set, the return value is a Python list (always a list, even if it is empty or contains only one node)

The following example prints out all bookmark URLs in the file, but is much simpler and more compact than the equivalent code earlier in this document:

bookmarks = doc.xml_xpath(u'//bookmark')
for bookmark in bookmarks:
    print bookmark.href
      

The following just returns all hrefs wherever they appear in the document, using an attribute query:

hrefs = doc.xml_xpath(u'//@href')
for href in hrefs:
    print unicode(href)
      

The following prints the title of the bookmark for the 4Suite project:

url = u"http://4suite.org/"
title_elements = doc.xml_xpath('//bookmark[@url="%s"]/title'%url)
#XPath node set expression always returns a list
print unicode(title_elements[0])
      

Bindery supports documents with namespaces. The following example displays a summary of the contents of an RSS 1.0 feed:

import amara

#Set up customary namespace bindings for RSS
#These are used in XPath query and XPattern rules
RSS10_NSS = {
    u'rdf': u'http://www.w3.org/1999/02/22-rdf-syntax-ns#',
    u'dc': u'http://purl.org/dc/elements/1.1/',
    u'rss': u'http://purl.org/rss/1.0/',
    }

doc = amara.parse('rss10.rdf', prefixes=RSS10_NSS)

#Create a dictionary of RSS items
items = {}
item_list = doc.xml_xpath(u'//rss:item')
items = dict( [ ( item.about, item) for item in item_list ] )
print items

for channel in doc.RDF.channel:
    print "Channel:", channel.about
    print "Title:", channel.title
    print "Items:"
    for item_ref in channel.items.Seq.li:
        item = items[item_ref.resource]
        print "\t", item.link
        print "\t", item.title
      

The following illustrates how namespace details are maintained in bindery objects:

#Show the namespace particulars of the rdf:RDF element
print doc.RDF.namespaceURI
print doc.RDF.localName
print doc.RDF.prefix
      

For attributes, xml_attributes is a dictionary containing namespace information for all of an element's attributes. See the Attributes section below for more details.

Namespaces work naturally with XPath as well:

#Get the RSS item with a given URL
item_url = u'http://www.oreillynet.com/cs/weblog/view/wlg/532'
matching_items = doc.RDF.xml_xpath(u'//rss:item[@rdf:about="%s"]'%item_url)
print matching_items
assert matching_items[0].about == item_url
      

In the above example I manually set the mapping from namespace prefixes to namespace names, but if your use of XML namespaces is "sane", you might not need this step. Bindery document objects automatically remember the namespace declarations made on the top level element of any document you parse.

The Python object reference and class names used in Amara bindings are based on the corresponding XML IDs, but there are limits to such mappings. For one thing, XML allows characters that are not allowed in Python IDs, such as -. In such cases Amara mangles the name. In the case of a document such as &lt;a-1 b-1=""/> you would access the element using doc.a_1, and the attribute using doc.a_1.b_1.

This can be problematic when writing generic code to address XML, because any element's name might be mangled in a different way depending on document context. You always have the option of accessing objects using their proper XML names in XPath:

doc.xml_xpath(u"a-1/b-1)

You can get the original XML name information from any object using properties named after DOMs:

• element.nodeName

• element.localName

• element.namespaceURI

• element.prefix

And you can get similar information on attributes by reading the xml_attributes dictionary on the element node.

If you're dealing with a large XML file, you may not want the entire data binding in memory at the same time. You may want to instantiate it bit by bit. If you have a clear pattern for how you want to break up the document, you can use the function amara.pushbind. See the following example:

import amara

for folder in amara.pushbind('xbel.xml', u'/xbel/folder'):
    title = folder.title
    bm_count = len(list(folder.bookmark))
    print "Folder", title, "has", bm_count, "top level bookmarks"
      

The neat thing is that this program doesn't have the entire binding in memory at time. In each iteration it loads just enough XML to represent each top-level folder element. pushbind is a generator that yields each little subtree each time it's invoked.

In general pushbind subtrees are Amara bindery objects based on the XSLT pattern that is passed in as its first argument. You also pass in an XML source, either a string (use the string= keyword) or a URI or file-name (use the source= keyword).

An interactive session helps illustrate:

>>> XML="""\
... <doc>
...   <one><a>0</a><a>1</a></one>
...   <two><a>10</a><a>11</a></two>
... </doc>
... """
>>> import amara
>>> chunks = amara.pushbind(XML, u'a')
>>> a = chunks.next()
>>> print a
0
>>> print a.xml()
<a>0</a>
>>> a = chunks.next()
>>> print a.xml()
<a>1</a>
>>> a = chunks.next()
>>> print a.xml()
<a>10</a>
>>> a = chunks.next()
>>> print a.xml()
<a>11</a>
>>> a = chunks.next()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
StopIteration

      

In the above case the XSLT pattern "a" matched all the elements with this name in the file. All the XML outside the "a" elements is essentially discarded by this code, so you have to tailor the XSLT pattern to include all the material you're interested in. In the following example, only the first two "a" elements are included in the generator yield.

        >>> chunks = amara.pushbind(XML, u'one/a')
>>> a = chunks.next()
>>> print a.xml()
<a>0</a>
>>> a = chunks.next()
>>> print a.xml()
<a>1</a>
>>> a = chunks.next()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
StopIteration
      

The pattern /doc/one/a would result in similar behavior for the sample document.

You can use namespaces in these patterns by using prefixes defined in a dictionary passed to pushbind.

import amara
#Set up customary namespace bindings for RSS
#These are used in XPath query and XPattern rules
RSS10_NSS = {
u'rdf': u'http://www.w3.org/1999/02/22-rdf-syntax-ns#',
u'dc': u'http://purl.org/dc/elements/1.1/',
u'rss': u'http://purl.org/rss/1.0/',
}

#Print out all titles in the RSS feed
items = amara.pushbind('demo/rss10.rdf', u'rss:item',
                               prefixes=RSS10_NSS)
for item in items:
    print item.title
#Print out all titles in the RSS feed, slightly different approach
chunks = amara.pushbind('demo/rss10.rdf', u'rss:item/rss:title',
                               prefixes=RSS10_NSS)
for title in chunks:
    print title

      

Modifying a binding is pretty straightforward. You can create or modify an attribute by simple assignment:

import amara
doc = amara.parse('monty.xml')
doc.monty.foo = u'bar'
doc.monty.spam = u'[attr modified]'
      

You can also replace an element's contents with a single text node, using similar notation:

        doc.monty.python = u'[elem 1 modified]\n'
doc.monty.python[1] = u'[elem 2 modified]\n'
      

The resut of the above code is:

<monty>
  <python spam="[attr modified]" foo="bar">[elem 1 modified]
</python>
  <python ministry="abuse">[elem 2 modified]
</python>
</monty>
      

You can empty out all children of an element:

doc.monty.python.xml_clear()
      

And add new elements and text. Create a new, empty element named new and append it as the last childof the first python element.

doc.monty.python.xml_append(doc.xml_create_element(u'new'))
      

Append a text node.

doc.monty.python.new.append(u'New Content')
      

You can insert new elements or text into specific locations, either before or after an existing child.

#Create a new `python` element as the second element child of `monty`
doc.monty.xml_insert_after(doc.monty.python,
                           doc.xml_create_element(u'python'))
#Create a new `python` element as the first element child of `monty`
doc.monty.xml_insert_before(doc.monty.python,
                            doc.xml_create_element(u'python'))
      

You can also delete a specific element, attribute, or text child:

del doc.monty.python
      

which does the same thing as

del doc.monty.python[0]
    

You can also use the xml_remove_child method:

        child = doc.monty.python
doc.monty.xml_remove_child(child)

      

Just to exhaustively list the approaches to deletion, you can use the position of an object among its siblings to remove it from its parent. You can get this position using the xml_index_on_parent property.

        ix = doc.monty.python.xml_index_on_parent
      

This assigns ix the value 1 since the first python element is the second child of monty.

ix = doc.monty.python[1].xml_index_on_parent
      

This assigns ix the value 3 since the second python element is the fourth child of monty. Once you have an index, you can use that index in order to delete a specific child by passing it to the xml_remove_child_at method:

doc.monty.xml_remove_child_at(3)
      

This removes the second python element, using the index determined above. This works for text as well:

doc.monty.xml_remove_child_at(0)
      

Removes the first text node. You can omit the index in the call to this method. By default it removes the last child:

doc.monty.xml_remove_child_at()
      

You can create a new element with a namespace:

e = doc.xml_create_element(element_qname, element_ns)
      

which is equivalent to

e = doc.xml_create_element(element_qname, namespace=element_ns)
      

You can easily add attributes while you're creating elements.

import amara
doc = amara.parse('monty.xml')
#Create a third python element
e = doc.xml_create_element(u'python', attributes={u'life': u'brian'})
doc.monty.xml_append(e)
print doc.xml()
      

This gives the following output:

<?xml version="1.0" encoding="UTF-8"?>
<monty>
  <python spam="eggs">
    What do you mean "bleh"
  </python>
  <python ministry="abuse">
    But I was looking for argument
  </python>
<python life="brian"/></monty>
      

You can see how the attribute is manifested on the new element.

The dictionary attributes={u'life': u'brian'} is actually a short-hand. The full form is:

{
  (<attr1_qname>, <attr1_namespace>): attr1_value},
  (<attr2_qname>, <attr2_namespace>): attr2_value},
  ...
  (<attrN_qname>, <attrN_namespace>): attrN_value},
}
      

But you can abbreviate (<attrN_qname>, <attrN_namespace>) to just <attrN_qname> if the namespace is None (i.e. the attribute is not in a namespace).

So you could add a namespace qualified attribute as follows:

import amara
NS = u'urn:bogus'
doc = amara.parse('monty.xml')
#Create a third python element
e = doc.xml_create_element(
     u'python',
     attributes={(u'ns:life', NS): u'brian'},
     content=u'unfortunate'
     )
doc.monty.xml_append(e)
print doc.xml()
     

Notice that this time I threw in some content as well. The result:

<?xml version="1.0" encoding="UTF-8"?>
<monty>
  <python spam="eggs">
    What do you mean "bleh"
  </python>
  <python ministry="abuse">
    But I was looking for argument
  </python>
<python xmlns:ns="urn:bogus" ns:life="brian">unfortunate</python></monty>
      

To create an attribute after the element is created, use the xml_set_attribute method. To add the namespace qualified attribute from the example above, use the following:

import amara
NS = u'urn:bogus'
doc = amara.parse('monty.xml')
#Create a third python element
e = doc.xml_create_element(
          u'python',
          content=u'unfortunate'
          )
doc.monty.xml_append(e)
doc.monty.python[2].xml_set_attribute((u'ns:life', NS), u'brian')
print doc.xml()
      

This produces the same XML as above. If no namespace is required, the first argument to xml_set_attribute is just the attribute name.

The xml_set_attribute method returns the name of the resulting attribute.

You can set an attribute's value using Python idiom as well:

doc.monty.python[2].life = u'Pi'
      

Information about an element's attributes, including namespace information, is kept in xml_attributes. This is a dictionary keyed by the local name of each attribute, with the value being a tuple of the namespace qualified attribute name and the namespace URL. For example, given the following code:

import amara
NS = u'urn:bogus'
doc = amara.parse('monty.xml')
#Create a third python element
e = doc.xml_create_element(
  u'python',
  content=u'unfortunate'
)
doc.monty.xml_append(e)
#Add a namespace qualified attribute
doc.monty.python[2].xml_set_attribute((u'ns:life', NS), u'brian')
#Add an attribute with no namespace
doc.monty.python[2].xml_set_attribute(u'foo', u'bar')
      

doc.monty.python[2].xml_attributes gives the value:

{u'life': (u'ns:life', u'urn:bogus'), u'foo': (u'foo', None)}
      

Just for fun, here's an interesting variation that illustrates the special status of the XML namespace.

import amara
from xml.dom import XML_NAMESPACE as XML_NS
doc = amara.parse('monty.xml')
#Create a third python element
e = doc.xml_create_element(
          u'python',
          attributes={(u'xml:lang', XML_NS): u'en'},
          content=u'Ni!'
          )
doc.monty.xml_append(e)
print doc.xml()
     

This gives the following output:

<?xml version="1.0" encoding="UTF-8"?>
<monty>
  <python spam="eggs">
    What do you mean "bleh"
  </python>
  <python ministry="abuse">
    But I was looking for argument
  </python>
<python xml:lang="en">Ni!</python></monty>

      

Notice that there's no declaration for the XML namespace, as allowed by the standard.

Amara offers a powerful facility for adding to XML documents through the xml_append_fragment method on elements. You pass this method a string (not Unicode, since this is a parse operation) with a fragment of literal XML which is parsed and added to the element. The XML fragment must be a well formed external parsed entity. Basically multiple root elements are allowed, but they must be properly balanced, special characters escaped, and so on. Doctype declaration is prohibited. According to XML rules, the encoded string is assumed to be UTF-8 or UTF-16, but you can override this with an XML text declaration (<?xml version="1.0" encoding="ENC"?>) or by passing in an encoding parameter to this function.

import amara
doc = amara.parse('monty.xml')
doc.monty.xml_append_fragment('<py3 x="1">p</py3><py4 y="2">q</py4>')
print doc.monty.xml_child_elements.keys()
      

The output is [u'python', u'py3', u'py4'], as two elements are added in the xml_append_fragment call.

The optional encoding is a string with the encoding to be used in parsing the XML fragment. If this parameter is specified, it overrrides any text declaration in the XML fragment.

#Latin-1 ordinal 230 is the a-e ligature
doc.monty.xml_append_fragment('<q>P%an</q>'%chr(230), 'latin-1')
      

You can create entire documents from scratch

doc = amara.create_document()
doc.xml_append(doc.xml_create_element(u"hello"))
doc.xml()
      

Yields

<?xml version="1.0" encoding="UTF-8"?>
<hello/>
      

You can specify a root element to be created in the empty document. The following code:

doc = amara.create_document(u"hello")
doc.hello.xml_append(doc.xml_create_element(u"world"))
doc.xml()

      

Yields

<?xml version="1.0" encoding="UTF-8"?>
<hello><world/></hello>
      

This is equivalent to:

doc = amara.create_document()
doc.xml_append(doc.xml_create_element(u"hello"))
doc.hello.xml_append(doc.xml_create_element(u"world"))
doc.xml()

      

You can set a namespace on the root element using the ns parameter. There are many other useful parameters. Try import amara; help(amara.create_document) at a Python prompt for more details.

If you're familiar with XSLT, you might wonder how to do the equivalent of xsl:copy-of in Amara. You can create such a deep copy using the copy module in the Python standard library.

import copy
import amara
doc = amara.parse('monty.xml')
#Clone the document
doc2 = copy.deepcopy(doc)
#This modification only affects the clone
doc2.monty.python.spam = u"abcd"

#This output will just like what was read in
print doc.xml()
#This output will show the change from "eggs" to "abcd"
print doc2.xml()
      

Bindery supports these XML constructs in a fairly natural way. If you have PIs or comments in a source document parsed into a binding, it will have objects representing the PIs and comments:

import amara
DOC = """\
<?xml-stylesheet url="xxx.css" type="text/css"?>
<!--A greeting for all-->
<hello-world/>
"""
doc = amara.parse(DOC)
print doc.xml_children
      

shows the following list:

[
<amara.bindery.pi_base instance at 0x433f6c>,
<amara.bindery.comment_base instance at 0x433fac>,
<amara.bindery.hello_world object at 0x433fec>
]
      

The first item is a bound PI object and the second a bound comment. You can dig deeper if you like:

pi = doc.xml_children[0]
comment = doc.xml_children[1]
print repr(pi.target) #shows u'xml-stylesheet'
print repr(pi.data) #shows u'url="xxx.css" type="text/css"'
print repr(comment.body) #shows u'A greeting for all'
      

You can also create or mutate these objects.

doc = amara.create_document()
pi = bindery.pi_base(u"xml-stylesheet", u'url="xxx.css" type="text/css"')
doc.xml_append(pi)
doc.xml_append(doc.xml_create_element(u"A"))
      

There is also an API for document type declarations (DTDecls).

To create a document with a DTDecl, do something like the following:

doc = amara.create_document(
    u"xsa",
    pubid=u"-//LM Garshol//DTD XML Software Autoupdate 1.0//EN//XML",
    sysid=u"http://www.garshol.priv.no/download/xsa/xsa.dtd"
    )
      

Which results in a tree equivalent to:

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE xsa PUBLIC "-//LM Garshol//DTD XML Software Autoupdate 1.0//EN//XML"
                     "http://www.garshol.priv.no/download/xsa/xsa.dtd">
<xsa/>
      

Notice how this automatically creates the document element for you (no need for a separate xml_append). You can expand on this to create attributes and content for the document element:

from xml.dom import XML_NAMESPACE as XML_NS

doc = amara.create_document(
    u"xsa",
    attributes={(u'xml:lang', XML_NS): u'en'},
    content=u' ',
    pubid=u"-//LM Garshol//DTD XML Software Autoupdate 1.0//EN//XML",
    sysid=u"http://www.garshol.priv.no/download/xsa/xsa.dtd"
    )

      

Which results in:

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE xsa PUBLIC "-//LM Garshol//DTD XML Software Autoupdate 1.0//EN//XML"                     "http://www.garshol.priv.no/download/xsa/xsa.dtd">
<xsa xml:lang="en"> </xsa>
      

You can then access the DTDecl details:

assert doc.xml_pubid == u"-//LM Garshol//DTD XML Software Autoupdate 1.0//EN//XML" 
assert doc.xml_sysid == u"http://www.garshol.priv.no/download/xsa/xsa.dtd"
assert doc.xml_doctype_name == u"xsa"
      

#DOES NOT YET WORK

XSA = """\
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE xsa PUBLIC "-//LM Garshol//DTD XML Software Autoupdate 1.0//EN//XML"                     "http://www.garshol.priv.no/download/xsa/xsa.dtd">
<xsa>
  <vendor>
    <name>Fourthought, Inc.</name>
    <email>info@fourthought.com</email>
    <url>http://fourthought.com</url>
  </vendor>
  <product id="FourSuite">
    <name>4Suite</name>
    <version>1.0a1</version>
    <last-release>20030327</last-release>
    <info-url>http://4suite.org</info-url>
    <changes>
 - Begin the 1.0 release cycle
    </changes>
  </product>
</xsa>
"""
doc = amara.parse(XSA)
assert doc.xml_pubid == u"-//LM Garshol//DTD XML Software Autoupdate 1.0//EN//XML"
assert doc.xml_sysid == u"http://www.garshol.priv.no/download/xsa/xsa.dtd"
assert doc.xml_doctype_name == u"xsa"
        

Bindery works by iterating over XML nodes and firing off a set of rules triggered by the node type and other details. The default binding is the result of the default rules that are registered for each node type, but Bindery makes this easy to tweak by letting you register your own rules.

Bindery comes bundled with 3 easy rule frameworks to handle some common binding needs.

import amara
from amara import binderytools
#Specify (using XSLT patterns) elements to be treated similarly to attributes
rules = [
    binderytools.simple_string_element_rule(u'title')
    ]
#Execute the binding
doc = amara.parse('xbel.xml', rules=rules)

#title is now simple unicode
print doc.xbel.folder.bookmark.title.__class__
	

import amara
from amara import binderytools
#Specify (using XSLT patterns) elements to be ignored
rules = [
    binderytools.omit_element_rule(u'folder/title')
    ]
#Execute the binding
doc = amara.parse('xbel.xml', rules=rules)

#Following would now raise an exception:
#print doc.xbel.folder.title
        

import amara
from amara import binderytools
#Specify (using XSLT patterns) elements to be stripped
#In this case select all top-level elements for stripping
rules = [
    binderytools.ws_strip_element_rule(u'/*')
    ]
#Execute the binding
doc = amara.parse('xbel.xml', rules=rules)
        

import amara
from amara import binderytools
#Specify (using XSLT patterns) elements to be bound as skeletons
#In this case select all elements
rules = [
    binderytools.element_skeleton_rule(u'*')
    ]
#Execute the binding
doc = amara.parse('xbel.xml', rules=rules)
        

TYPE_MIX = """\
<?xml version="1.0" encoding="utf-8"?>
<a a1="1">
  <b b1="2.1"/>
  <c c1="2005-01-31">
    <d>5</d>
  <e>2003-01-30T17:48:07.848769Z</e>
  </c>
  <g>good</g>
</a>"""

import amara
from amara import binderytools
rules=[binderytools.type_inference()]
doc = amara.parse(TYPE_MIX, rules=rules)
doc.a.a1 == 1     #type int
doc.a.b.b1 == 2.1 #type float
doc.a.c.c1 == datetime.datetime(2005, 1, 31) #type datetime.
        

import amara
from amara import binderytools
#Set up customary namespace bindings for RSS
#These are used in XPath query and XPattern rules
RSS10_NSS = {
    'rdf': 'http://www.w3.org/1999/02/22-rdf-syntax-ns#',
    'dc': 'http://purl.org/dc/elements/1.1/',
    'rss': 'http://purl.org/rss/1.0/',
    }

rules = [
    binderytools.simple_string_element_rule(u'title')
    ]
#Execute the binding
doc = amara.parse('rss10.rdf', prefixes=RSS10_NSS, rules=rules)
        

You can also use rules with pushbind. If all you ever want from "a" elements is to extract the text content, you could do something like the following. Look carefully: the sample document is slightly different this time.

>>> XML="""\
... <doc>
...   <one><a>0</a><b>1</b></one>
...   <two><a>10</a><b>11</b></two>
... </doc>
... """
>>> import amara
>>> from amara import binderytools
>>> #This rule says "treat all elements at the third level of depth as simple strings"
>>> rule = binderytools.simple_string_element_rule(u'/*/*/*')
>>> #Push back bindings of all second level elements ('one' and 'two')
>>> chunks = amara.pushbind(XML, u'/*/*', rules=[rule])
>>> elem = chunks.next()
>>> print elem.a.__class__
<type 'unicode'>
>>> print elem.a
u'0'
>>> print elem.b.__class__
<type 'unicode'>
>>> print elem.b
u'1'
      

If you need more sophisticated tweaking, you proably want to register your own customized binding class. The following example gives bookmark elements a method, retrieve, which retrieves the body of the Web page:

import urllib
from xml.dom import Node
import amara
from amara import bindery
from Ft.Xml import InputSource
from Ft.Lib import Uri

#Subclass from the default binding class
#We're adding a specialized method for accessing a bookmark on the net
class specialized_bookmark(bindery.element_base):
    def retrieve(self):
        try:
            stream = urllib.urlopen(self.href)
            content = stream.read()
            stream.close()
            return content
        except IOError:
            import sys; sys.stderr.write("Unable to access %s\n"%self.href)

#Explicitly create a binder instance, in order to customize rules
binder = bindery.binder()

#associate specialized_bookmark class with elements not in an XML
#namespace and having a GI of "bookmark"
binder.set_binding_class(None, "bookmark", specialized_bookmark)

#Execute the binding
doc = amara.parse('xbel.xml', binderobj=binder)

#Show specialized instance
print doc.xbel.folder.bookmark.__class__

#Exercise the custom method
print "Content of first bookmark:"
print doc.xbel.folder.bookmark.retrieve()
      

Focus on the line:

binder.set_binding_class(None, "bookmark", specialized_bookmark)
      

When you register classes to use in binding a given elements type you do so by specifying namespace URI and local name of the element. If you know that the element is not in a namespace, as in the XBEL example, you use None. None is the Right Way to signal "not in a namespace" in most Python/XML tools, and not the empty string "".

Bindery is designed to be extensible, but this is not a simple proposition given the huge flexibility of XML expression, and the many different ways developpers might want to generate resulting Python objects (and vice versa). You can pretty much do whatever you need to by writing Bindery extensions, but in order to keep things basically manageable, there are some ground rules.

You're probably familiar with xml.dom.pulldom, which offers a nice hybrid between SAX and DOM, allowing you to efficiently isolate important parts of a document in a SAX-like manner, and then using DOM for finer-grained manipulation. Amara's pushdom makes this process even more convenient You give it a set of XPatterns, and it provides a generator yielding a series of DOM chunks according to the patterns.

In this way you can process huge files with very little memory usage, but most of the convenience of DOM.

for docfrag in domtools.pushdom('demo/labels.xml', u'/labels/label'):
    label = docfrag.firstChild
    name = label.xpath('string(name)')
    city = label.xpath('string(address/city)')
    if name.lower().find('eliot') != -1:
        print city.encode('utf-8')
      

Prints "Stamford".

See also this XML-DEV message.

For more on the generator tools see the article "Generating DOM Magic".

domtools.abs_path allows you to get the absolute path for a node. The following code:

from amara import domtools
from Ft.Xml.Domlette import NonvalidatingReader
from Ft.Lib import Uri
file_uri = Uri.OsPathToUri('labels.xml', attemptAbsolute=1)
doc = NonvalidatingReader.parseUri(file_uri)

print domtools.abs_path(doc)
print domtools.abs_path(doc.documentElement)
for node in doc.documentElement.childNodes:
    print domtools.abs_path(node)
      

Displays:

/
/labels[1]
/labels[1]/text()[1]
/labels[1]/label[1]
/labels[1]/text()[2]
/labels[1]/label[2]
/labels[1]/text()[3]
/labels[1]/label[3]
/labels[1]/text()[4]
/labels[1]/label[4]
/labels[1]/text()[5]
      

For more on abs_path tools see the article "Location, Location, Location".