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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def getTreeWalker(treeType, implementation=None, **kwargs):
 """Get a TreeWalker class for various types of tree with built-in support :arg str treeType: the name of the tree type required (case-insensitive). Supported values are: * "dom": The xml.dom.minidom DOM implementation * "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 * "genshi": a Genshi stream :arg implementation: A module implementing the tree type e.g. xml.etree.ElementTree or cElementTree (Currently applies to the "etree" tree type only). :arg kwargs: keyword arguments passed to the etree walker--for other walkers, this has no effect :returns: a TreeWalker class """


    treeType = treeType.lower()
    if treeType not in treeWalkerCache:
        if treeType == "dom":
            from . import dom
            treeWalkerCache[treeType] = dom.TreeWalker
        elif treeType == "genshi":
            from . import genshi
            treeWalkerCache[treeType] = genshi.TreeWalker
        elif treeType == "lxml":
            from . import etree_lxml
            treeWalkerCache[treeType] = etree_lxml.TreeWalker
        elif treeType == "etree":
            from . import etree
            if implementation is None:
                implementation = default_etree
            # XXX: NEVER cache here, caching is done in the etree submodule
            return etree.getETreeModule(implementation, **kwargs).TreeWalker
    return treeWalkerCache.get(treeType)