parameters: (ops, cur_op, var_name)
return_statement: return None
docstring: Find the true prev op that outputs var_name variable.
  
      Args:
          ops (list): A list of ops.
          cur_op (Operator): Current operator which has var_name variable.
          var_name (string): Variable name.
docstring_summary: Find the true prev op that outputs var_name variable.
docstring_tokens: Find the true prev op that outputs var_name variable .
function: def find_true_prev_op(ops, cur_op, var_name):
      """
      Find the true prev op that outputs var_name variable.
  
      Args:
          ops (list): A list of ops.
          cur_op (Operator): Current operator which has var_name variable.
          var_name (string): Variable name.
      """
      prev_op = []
      for op in ops:
          if op == cur_op:
              break
          for out_name in op.output_names:
              for out_var_name in op.output(out_name):
                  if out_var_name == var_name:
                      prev_op.append(op)
      if prev_op:
          if not len(prev_op) == 1:
              raise ValueError("There must be only one previous op "
                               "that outputs {0} variable".format(var_name))
          else:
              return prev_op[0]
      return None
function_tokens: def find_true_prev_op ( ops , cur_op , var_name ) : prev_op = [ ] for op in ops : if op == cur_op : break for out_name in op . output_names : for out_var_name in op . output ( out_name ) : if out_var_name == var_name : prev_op . append ( op ) if prev_op : if not len ( prev_op ) == 1 : raise ValueError ( "There must be only one previous op " "that outputs {0} variable" . format ( var_name ) ) else : return prev_op [ 0 ] return None