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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 get_cachedir_csig(self):
 """ Fetch a Node's content signature for purposes of computing another Node's cachesig. This is a wrapper around the normal get_csig() method that handles the somewhat obscure case of using CacheDir with the -n option. Any files that don't exist would normally be "built" by fetching them from the cache, but the normal get_csig() method will try to open up the local file, which doesn't exist because the -n option meant we didn't actually pull the file from cachedir. But since the file *does* actually exist in the cachedir, we can use its contents for the csig. """

        try:
            return self.cachedir_csig
        except AttributeError:
            pass

        cachedir, cachefile = self.get_build_env().get_CacheDir().cachepath(self)
        if not self.exists() and cachefile and os.path.exists(cachefile):
            self.cachedir_csig = SCons.Util.MD5filesignature(cachefile, \
                SCons.Node.FS.File.md5_chunksize * 1024)
        else:
            self.cachedir_csig = self.get_csig()
        return self.cachedir_csig