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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 _compute_unnecessary_deps(self, target, actual_deps):
 """Computes unused deps for the given Target. :returns: A dict of directly declared but unused targets, to sets of suggested replacements. """

    # Flatten the product deps of this target.
    product_deps = set()
    for dep_entries in actual_deps.values():
      product_deps.update(dep_entries)

    # Determine which of the DEFAULT deps in the declared set of this target were used.
    used = set()
    unused = set()
    for dep, _ in self._analyzer.resolve_aliases(target, scope=Scopes.DEFAULT):
      if dep in used or dep in unused:
        continue
      # TODO: What's a better way to accomplish this check? Filtering by `has_sources` would
      # incorrectly skip "empty" `*_library` targets, which could then be used as a loophole.
      if isinstance(dep, (Resources, UnpackedJars)):
        continue
      # If any of the target's jars or classfiles were used, consider it used.
      if product_deps.isdisjoint(self._analyzer.files_for_target(dep)):
        unused.add(dep)
      else:
        used.add(dep)

    # If there were no unused deps, break.
    if not unused:
      return {}

    # For any deps that were used, count their derived-from targets used as well.
    # TODO: Refactor to do some of this above once tests are in place.
    for dep in list(used):
      for derived_from in dep.derived_from_chain:
        if derived_from in unused:
          unused.remove(derived_from)
          used.add(derived_from)

    # Prune derived targets that would be in the set twice.
    for dep in list(unused):
      if set(dep.derived_from_chain) & unused:
        unused.remove(dep)

    if not unused:
      return {}

    # For any deps that were not used, determine whether their transitive deps were used, and
    # recommend those as replacements.
    replacements = {}
    for dep in unused:
      replacements[dep] = set()
      for t in dep.closure():
        if t in used or t in unused:
          continue
        if not product_deps.isdisjoint(self._analyzer.files_for_target(t)):
          replacements[dep].add(t.concrete_derived_from)

    return replacements