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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 escape(string, quote=False):
 """Standard HTML text escaping, but protecting against the agressive behavior of Jinja 2 `Markup` and the like. """

    if string is None:
        return ''
    elif hasattr(string, '__html__'):
        return unicode(string)
    string = string.replace('&', '&amp;').replace('<', '&lt;').replace('>', '&gt;')
    if quote:
        string = string.replace('"', "&quot;")
    return string