def execute(self):
    if self.goal not in PrepCommand.goals():
      raise  AssertionError('Got goal "{}". Expected goal to be one of {}'.format(
          self.goal, PrepCommand.goals()))

    targets = self.context.targets(postorder=True,  predicate=self.runnable_prep_cmd)
    Cmdline = namedtuple('Cmdline', ['cmdline', 'environ'])

    def make_cmdline(target):
      executable = target.payload.get_field_value('prep_command_executable')
      args = target.payload.get_field_value('prep_command_args', [])
      prep_environ = target.payload.get_field_value('prep_environ')
      cmdline = [executable]
      cmdline.extend(args)
      return Cmdline(cmdline=tuple(cmdline), environ=prep_environ)

    def has_prep(target):
      return target.payload.get_field_value('prep_command_executable')

    cmdlines = [make_cmdline(target) for target in targets if has_prep(target)]

    if not cmdlines:
      return

    with self.context.new_workunit(name='prep_command', labels=[WorkUnitLabel.PREP]) as workunit:
      completed_cmdlines = set()
      for item in cmdlines:
        cmdline = item.cmdline
        environ = item.environ
        if not cmdline in completed_cmdlines:
          completed_cmdlines.add(cmdline)
          stderr = workunit.output('stderr') if workunit else None
          try:
            process = subprocess.Popen(cmdline, stdout=subprocess.PIPE, stderr=stderr)
          except __HOLE__ as e:
            workunit.set_outcome(WorkUnit.FAILURE)
            raise TaskError('RunPrepCommand failed to execute {cmdline}: {error}'.format(
              cmdline=cmdline, error=e))
          stdout, _ = process.communicate()

          if environ:
            if not process.returncode:
              environment_vars = stdout.split('\0')
              for kvpair in environment_vars:
                var, value = kvpair.split('=', 1)
                os.environ[var] = value
          else:
            if workunit:
              workunit.output('stdout').write(stdout)

          workunit.set_outcome(WorkUnit.FAILURE if process.returncode else WorkUnit.SUCCESS)
          if process.returncode:
            raise TaskError('RunPrepCommand failed to run {cmdline}'.format(cmdline=cmdline))
dataset/ETHPy150Open pantsbuild/pants/src/python/pants/core_tasks/run_prep_command.py/RunPrepCommandBase.execute