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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 _font_of_mention(m):
 """ Returns the font type and size of the first alphanumeric char in the text or None if there isn't any. """

    for ch in m:
        if isinstance(ch, LTChar) and ch.get_text().isalnum():
            return (ch.fontname, _font_size_of(ch))
    return (None, 0)