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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 findunique(lst, key):
 """ Find all unique key values for items in lst. Parameters lst: list A list of composite dictionaries e.g. ``layers``, ``classes`` key: string The key name to search each dictionary in the list Returns ------- list A sorted Python list of unique keys in the list Example ------- To find all ``GROUP`` values for ``CLASS`` in a ``LAYER``:: s = ''' LAYER CLASS GROUP "group1" NAME "Class1" COLOR 0 0 0 END CLASS GROUP "group2" NAME "Class2" COLOR 0 0 0 END CLASS GROUP "group1" NAME "Class3" COLOR 0 0 0 END END ''' d = mappyfile.loads(s) groups = mappyfile.findunique(d["classes"], "group") assert groups == ["group1", "group2"] """

    return sorted(set([item[key.lower()] for item in lst]))