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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 find_notebook(fullname, path=None):
 """find a notebook, given its fully qualified name and an optional path This turns "foo.bar" into "foo/bar.ipynb" and tries turning "Foo_Bar" into "Foo Bar" if Foo_Bar does not exist. """

    name = fullname.rsplit('.', 1)[-1]
    if not path:
        path = ['']
    for d in path:
        nb_path = os.path.join(d, name + ".ipynb")
        if os.path.isfile(nb_path):
            return nb_path
        # let import Notebook_Name find "Notebook Name.ipynb"
        nb_path = nb_path.replace("_", " ")
        if os.path.isfile(nb_path):
            return nb_path