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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 walk(self, func, arg):
 """ Walk this directory tree by calling the specified function for each directory in the tree. This behaves like the os.path.walk() function, but for in-memory Node.FS.Dir objects. The function takes the same arguments as the functions passed to os.path.walk():
 func(arg, dirname, fnames) Except that "dirname" will actually be the directory *Node*, not the string. The '.' and '..' entries are excluded from fnames. The fnames list may be modified in-place to filter the subdirectories visited or otherwise impose a specific order. The "arg" argument is always passed to func() and may be used in any way (or ignored, passing None is common). """

        entries = self.entries
        names = list(entries.keys())
        names.remove('.')
        names.remove('..')
        func(arg, self, names)
        for dirname in [n for n in names if isinstance(entries[n], Dir)]:
            entries[dirname].walk(func, arg)