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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 get_plaintext_document_body(fpath, keep_layout=False):
 """Given a file-path to a full-text, return a list of unicode strings whereby each string is a line of the fulltext. In the case of a plain-text document, this simply means reading the contents in from the file. In the case of a PDF however, this means converting the document to plaintext. It raises UnknownDocumentTypeError if the document is not a PDF or plain text. @param fpath: (string) - the path to the fulltext file @return: (list) of strings - each string being a line in the document. """

    textbody = []
    mime_type = magic.from_file(fpath, mime=True)

    if mime_type == "text/plain":
        with open(fpath, "r") as f:
            textbody = [line.decode("utf-8") for line in f.readlines()]

    elif mime_type == "application/pdf":
        textbody = convert_PDF_to_plaintext(fpath, keep_layout)

    else:
        raise UnknownDocumentTypeError(mime_type)

    return textbody