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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 make_cache_key(custom_kbs_files=None):
 """Create cache key for kbs caches instances This function generates a unique key for a given set of arguments. The files dictionary is transformed like this: {'journal': '/var/journal.kb', 'books': '/var/books.kb'} to "journal=/var/journal.kb;books=/var/books.kb" Then _inspire is appended if we are an INSPIRE site. """

    if custom_kbs_files:
        serialized_args = ('%s=%s' % v for v in iteritems(custom_kbs_files))
        serialized_args = ';'.join(serialized_args)
    else:
        serialized_args = "default"
    cache_key = md5(serialized_args).digest()
    return cache_key