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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 to_source(node, indentation=' ' * 4):
 """Return source code of a given AST."""

  if isinstance(node, gast.AST):
    node = gast.gast_to_ast(node)
  generator = SourceWithCommentGenerator(indentation, False,
                                         astor.string_repr.pretty_string)
  generator.visit(node)
  generator.result.append('\n')
  return astor.source_repr.pretty_source(generator.result).lstrip()