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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 _summarize_accessible_fields(field_descriptions, width=40, section_title='Accessible fields'):
 """ Create a summary string for the accessible fields in a model. Unlike `_toolkit_repr_print`, this function does not look up the values of the fields, it just formats the names and descriptions. Parameters field_descriptions : dict{str: str} Name of each field and its description, in a dictionary. Keys and values should be strings. width : int, optional Width of the names. This is usually determined and passed by the calling `__repr__` method. section_title : str, optional Name of the accessible fields section in the summary string. Returns ------- out : str """

    key_str = "{:<{}}: {}"

    items = []
    items.append(section_title)
    items.append("-" * len(section_title))

    for field_name, field_desc in field_descriptions.items():
        items.append(key_str.format(field_name, width, field_desc))

    return "\n".join(items)