code: def get_default_version(env):
      
      if 'MSVS' not in env or not SCons.Util.is_Dict(env['MSVS']):
          # get all versions, and remember them for speed later
          versions = [vs.version for vs in get_installed_visual_studios()]
          env['MSVS'] = {'VERSIONS' : versions}
      else:
          versions = env['MSVS'].get('VERSIONS', [])
  
      if 'MSVS_VERSION' not in env:
          if versions:
              env['MSVS_VERSION'] = versions[0] #use highest version by default
          else:
              debug('get_default_version: WARNING: no installed versions found, '
                    'using first in SupportedVSList (%s)'%SupportedVSList[0].version)
              env['MSVS_VERSION'] = SupportedVSList[0].version
  
      env['MSVS']['VERSION'] = env['MSVS_VERSION']
  
      return env['MSVS_VERSION']
docs: Returns the default version string to use for MSVS.
  
      If no version was requested by the user through the MSVS environment
      variable, query all the available visual studios through
      get_installed_visual_studios, and take the highest one.
  
      Return
      ------
      version: str
          the default version.