class_docstr: Transforms list comprehension into genexp
  >>> import gast as ast
  >>> from pythran import passmanager, backend
  >>> node = ast.parse("""                   \ndef foo(l):                                    \n    return builtins.sum(l)                     \ndef bar(n):                                    \n    return foo([x for x in builtins.range(n)]) """)
  >>> pm = passmanager.PassManager("test")
  >>> _, node = pm.apply(ListCompToGenexp, node)
  >>> print(pm.dump(backend.Python, node))
  def foo(l):
      return builtins.sum(l)
  def bar(n):
      return foo((x for x in builtins.range(n)))
code: def visit_ListComp(self, node):
      self.generic_visit(node)
      if node in self.potential_iterator:
          self.update = True
          return ast.GeneratorExp(node.elt, node.generators)
      else:
          return node
  
imports: from pythran.analyses import PotentialIterator
  from pythran.passmanager import Transformation
  import gast
label_desc: Use image node_id 2 for calling the ListCompToGenexp obj's underlying member method code with example usage: obj.visit_ListComp(node) and returns: ast, node