old_contents: from setuptools import Extension
  from setuptools import setup
  
  
  setup(
      name='dockerfile',
      description=(
          'Parse a dockerfile into a high-level representation using the '
          'official go parser.'
      ),
      url='https://github.com/asottile/dockerfile',
      version='0.0.0',
      author='Anthony Sottile',
      author_email='asottile@umich.edu',
      classifiers=[
          'License :: OSI Approved :: MIT License',
          'Programming Language :: Python :: 2',
          'Programming Language :: Python :: 2.7',
          'Programming Language :: Python :: 3',
          'Programming Language :: Python :: 3.5',
          'Programming Language :: Python :: 3.6',
          'Programming Language :: Python :: Implementation :: CPython',
          'Programming Language :: Python :: Implementation :: PyPy',
      ],
      ext_modules=[
          Extension('dockerfile', ['pylib/main.go']),
      ],
      build_golang={'root': 'github.com/asottile/dockerfile'},
      setup_requires=['setuptools-golang>=0.2.0'],
  )
  
new_contents: import os
  
  from setuptools import Extension
  from setuptools import setup
  
  
  if not os.path.exists('vendor/github.com/docker/docker/builder'):
      print('docker checkout is missing!')
      print('Run `git submodule update --init`')
      exit(1)
  
  
  setup(
      name='dockerfile',
      description=(
          'Parse a dockerfile into a high-level representation using the '
          'official go parser.'
      ),
      url='https://github.com/asottile/dockerfile',
      version='0.0.0',
      author='Anthony Sottile',
      author_email='asottile@umich.edu',
      classifiers=[
          'License :: OSI Approved :: MIT License',
          'Programming Language :: Python :: 2',
          'Programming Language :: Python :: 2.7',
          'Programming Language :: Python :: 3',
          'Programming Language :: Python :: 3.5',
          'Programming Language :: Python :: 3.6',
          'Programming Language :: Python :: Implementation :: CPython',
          'Programming Language :: Python :: Implementation :: PyPy',
      ],
      ext_modules=[
          Extension('dockerfile', ['pylib/main.go']),
      ],
      build_golang={'root': 'github.com/asottile/dockerfile'},
      setup_requires=['setuptools-golang>=0.2.0'],
  )
  
subject: Add guard against submodule