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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 group_by(resources, key):
 """Return a mapping of key value to resources with the corresponding value. Key may be specified as dotted form for nested dictionary lookup """

    resource_map = {}
    parts = key.split('.')
    for r in resources:
        v = r
        for k in parts:
            v = v.get(k)
            if not isinstance(v, dict):
                break
        resource_map.setdefault(v, []).append(r)
    return resource_map