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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 prettystr(subtree):
 """Print an element tree with nice indentation. Prettyprinting a whole VOEvent often doesn't seem to work, probably for issues relating to whitespace cf. http://lxml.de/FAQ.html#why-doesn-t-the-pretty-print-option-reformat-my-xml-output This function is a quick workaround for prettyprinting a subsection of a VOEvent, for easier desk-checking. Args: subtree(:class`lxml.etree.ElementTree`):
 A node in the VOEvent element tree. Returns: str: Prettyprinted string representation of the raw XML. """

    subtree = deepcopy(subtree)
    lxml.objectify.deannotate(subtree)
    lxml.etree.cleanup_namespaces(subtree)
    return lxml.etree.tostring(subtree, pretty_print=True).decode(
        encoding="utf-8")