def fa_attachment(extension):
    """
    Add fontawesome icon if found. Else return normal extension as string.

    :param extension: file extension
    :return: matching fontawesome icon as string
    """
    if extension == 'pdf':
        return "<i class='fa fa-file-pdf-o fa-lg'></i>"
    elif extension == 'jpg' or extension == 'png':
        return "<i class='fa fa-picture-o fa-lg'></i>"
    elif extension == 'doc' or extension == 'docx':
        return "<i class='fa fa-file-word-o fa-lg'></i>"
    elif extension == 'xls' or extension == 'xlsx':
        return "<i class='fa fa-file-excel-o fa-lg'></i>"
    elif extension == 'extern':
        return "<i class='fa fa-external-link'></i>"
    elif extension == 'zip':
        return "<i class='fa fa-file-archive-o fa-lg'></i>"
    else:
        return extension