"""A collection of modules for iterating through different kinds of

tree, generating tokens identical to those produced by the tokenizer

module.

To create a tree walker for a new type of tree, you need to do

implement a tree walker object (called TreeWalker by convention) that

implements a 'serialize' method taking a tree as sole argument and

returning an iterator generating tokens.

"""

treeWalkerCache = {}

def getTreeWalker(treeType, implementation=None, **kwargs):

"""Get a TreeWalker class for various types of tree with built-in support

treeType - the name of the tree type required (case-insensitive). Supported

values are "simpletree", "dom", "etree" and "beautifulsoup"

"simpletree" - a built-in DOM-ish tree type with support for some

more pythonic idioms.

"dom" - The xml.dom.minidom DOM implementation

"pulldom" - The xml.dom.pulldom event stream

"etree" - A generic walker for tree implementations exposing an

elementtree-like interface (known to work with

ElementTree, cElementTree and lxml.etree).

"lxml" - Optimized walker for lxml.etree

"beautifulsoup" - Beautiful soup (if installed)

"genshi" - a Genshi stream

implementation - (Currently applies to the "etree" tree type only). A module

implementing the tree type e.g. xml.etree.ElementTree or

cElementTree."""

treeType = treeType.lower()

if treeType not in treeWalkerCache:

if treeType in ("dom", "pulldom", "simpletree"):

mod = __import__(treeType, globals())

treeWalkerCache[treeType] = mod.TreeWalker

elif treeType == "genshi":

from . import genshistream

treeWalkerCache[treeType] = genshistream.TreeWalker

elif treeType == "beautifulsoup":

from . import soup

treeWalkerCache[treeType] = soup.TreeWalker

elif treeType == "lxml":

from . import lxmletree

treeWalkerCache[treeType] = lxmletree.TreeWalker

elif treeType == "etree":

from . import etree

if implementation is None:

try:

from xml.etree import cElementTree as etree

except:

from xml.etree import ElementTree as etree

implementation = etree

# XXX: NEVER cache here, caching is done in the etree submodule

return etree.getETreeModule(implementation, **kwargs).TreeWalker

return treeWalkerCache.get(treeType)