text: # Copyright 2018 Google Inc.
  #
  # Redistribution and use in source and binary forms, with or without
  # modification, are permitted provided that the following conditions
  # are met:
  #
  # 1. Redistributions of source code must retain the above copyright notice,
  #    this list of conditions and the following disclaimer.
  #
  # 2. Redistributions in binary form must reproduce the above copyright
  #    notice, this list of conditions and the following disclaimer in the
  #    documentation and/or other materials provided with the distribution.
  #
  # 3. Neither the name of the copyright holder nor the names of its
  #    contributors may be used to endorse or promote products derived from this
  #    software without specific prior written permission.
  #
  # THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
  # AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  # IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  # ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
  # LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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  # SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
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  # POSSIBILITY OF SUCH DAMAGE.
  """Helpers for running a command."""
  
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  import logging
  import subprocess
  import time
  
  
  def run_command(args, std_input=None, retry_delay_sec=1, retries=0):
    """Runs a command with optional retry behaviour.
  
    Args:
      args: (list) A list of arguments (type string) to pass to Popen.
      std_input: (str) will be passed as stdin to the command.
      retry_delay_sec: (int) delay in retries.
      retries: (int) number of retries.
  
    Returns:
      stdout.
  
    Raises:
      ValueError: if number of retries is less than zero.
      RuntimeError: if process returns a non-zero exit code in all retries.
    """
    if retries < 0:
      raise ValueError('Number of retries cannot be negative.')
  
    logging.debug('Calling command: %s', ' '.join(args))
    for i in range(retries + 1):
      if std_input:
        process = subprocess.Popen(
            args,
            stdin=subprocess.PIPE,
            stdout=subprocess.PIPE,
            stderr=subprocess.PIPE)
        stdout, stderr = process.communicate(input=std_input)
      else:
        process = subprocess.Popen(
            args, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        stdout, stderr = process.communicate()
      if process.returncode == 0:
        if stderr:
          logging.info('%s succeeded with stderr: %s', ' '.join(args), stderr)
        return stdout
      logging.warning('%s exited with code %d: %s', ' '.join(args),
                      process.returncode, (stdout + stderr).strip())
      if i < retries:
        logging.warning('Retrying command (attempt %d/%d): ', i + 1, retries)
        time.sleep(retry_delay_sec)
    raise RuntimeError(
        '%s failed after %d attempts.' % (' '.join(args), retries + 1))
  