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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 relation_types():
 """Get a list of relation types supported by this charm"""

    rel_types = []
    md = metadata()
    for key in ('provides', 'requires', 'peers'):
        section = md.get(key)
        if section:
            rel_types.extend(section.keys())
    return rel_types