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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 exists_using_casper(self, filename):
 """Check for the existence of a package file. Unlike other DistributionPoint types, JDS and CDP types have no documented interface for checking whether the server and its children have a complete copy of a file. The best we can do is check for an object using the API /packages URL--JSS.Package() or /scripts and look for matches on the filename. If this is not enough, this method uses the results of the casper.jxml page to determine if a package exists. This is an undocumented feature and as such should probably not be relied upon. Please note, scripts are not listed per-distributionserver like packages. For scripts, the best you can do is use the regular exists method. It will test for whether the file exists on ALL configured distribution servers. This may register False if the JDS is busy syncing them. """

        casper_results = casper.Casper(self.connection["jss"])
        distribution_servers = casper_results.find("distributionservers")

        # Step one: Build a list of sets of all package names.
        all_packages = []
        for distribution_server in distribution_servers:
            packages = set()
            for package in distribution_server.findall("packages/package"):
                packages.add(os.path.basename(package.find("fileURL").text))

            all_packages.append(packages)

        # Step two: Intersect the sets.
        base_set = all_packages.pop()
        for packages in all_packages:
            base_set = base_set.intersection(packages)

        # Step three: Check for membership.
        return filename in base_set