class_docstr: Represents an undefined symbol in Python.
  
  This is used to reify undefined symbols, which is required to use the
  functional form of loops.
  Example:
  
    while n > 0:
      n = n - 1
      s = n
    return s  # Runtime error if n == 0
  
  This is valid Python code and will not result in an error as long as n
  is positive. The use of this class is to stay as close to Python semantics
  as possible for staged code of this nature.
  
  Converted version of the above showing the possible usage of this class:
  
    s = Undefined('s')
    init_state = (s,)
    s = while_loop(cond, body, init_state)
    return s  # s is an instance of Undefined if the loop never runs
  
  Attributes:
    symbol_name: Text, identifier for the undefined symbol
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code: def __getitem__(self, i):
      return self
  
file_path: tensorflow/tensorflow/python/autograph/operators/variables.py
label_desc: Use image node_id 5 for calling the Undefined obj's underlying member method code with example usage: obj.__getitem__(i) and returns: self