old_contents: #!/usr/bin/env python
  # Copyright 2019 Google Inc.
  # Use of this source code is governed by a BSD-style license that can be
  # found in the LICENSE file.
  
  import os
  import sys
  import subprocess
  
  '''
  Look for the first match in the format
      C:\\Program Files (x86)\\Microsoft Visual Studio\\${RELEASE}\\${VERSION}\\VC
  '''
  def find_msvc():
    if sys.platform.startswith('win'):
      default_dir = r'C:\Program Files (x86)\Microsoft Visual Studio'
      for release in ['2019', '2017']:
        for version in ['Enterprise', 'Professional', 'Community', 'BuildTools']:
          path = os.path.join(default_dir, release, version, 'VC')
          if os.path.isdir(path):
            return path
  
      # Fall back to vswhere.exe to determine non-standard installation paths
      # Fixed location, https://github.com/Microsoft/vswhere/wiki/Installing
      vswhere = os.path.join(os.getenv('ProgramFiles(x86)'),
                'Microsoft Visual Studio', 'Installer', 'vswhere.exe')
      command = (vswhere + ' -prerelease -legacy -products * -sort -utf8 '
                '-property installationPath')
      paths = subprocess.check_output(command).decode('utf-8').splitlines()
      if paths:
        return paths[0] + '\\VC'
  
    return None
  
  if __name__ == '__main__':
    result = find_msvc()
    if result:
      sys.stdout.write(result + '\n')
  
new_contents: #!/usr/bin/env python
  # Copyright 2019 Google Inc.
  # Use of this source code is governed by a BSD-style license that can be
  # found in the LICENSE file.
  
  import os
  import sys
  import subprocess
  
  '''
  Look for the first match in the format
      C:\\Program Files (x86)\\Microsoft Visual Studio\\${RELEASE}\\${VERSION}\\VC
  '''
  def find_msvc():
    if sys.platform.startswith('win'):
      default_dir = r'C:\Program Files (x86)\Microsoft Visual Studio'
      for release in ['2019', '2017']:
        for version in ['Enterprise', 'Professional', 'Community', 'BuildTools', 'Preview']:
          path = os.path.join(default_dir, release, version, 'VC')
          if os.path.isdir(path):
            return path
  
      # Fall back to vswhere.exe to determine non-standard installation paths
      # Fixed location, https://github.com/Microsoft/vswhere/wiki/Installing
      vswhere = os.path.join(os.getenv('ProgramFiles(x86)'),
                'Microsoft Visual Studio', 'Installer', 'vswhere.exe')
      command = (vswhere + ' -prerelease -legacy -products * -sort -utf8 '
                '-property installationPath')
      paths = subprocess.check_output(command).decode('utf-8').splitlines()
      if paths:
        return paths[0] + '\\VC'
  
    return None
  
  if __name__ == '__main__':
    result = find_msvc()
    if result:
      sys.stdout.write(result + '\n')
  
subject: Add Preview to list of possible MSVC versions.