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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 variable_names(self):
 """ Returns the names of all environment variables. :return: the names of the variables :rtype: list """

        result = []
        names = javabridge.call(self.jobject, "getVariableNames", "()Ljava/util/Set;")
        for name in javabridge.iterate_collection(names):
            result.append(javabridge.to_string(name))
        return result