code: def Session(access_token=None, env=None):
      
      if env is None:
          env = os.environ.copy()
      access_token = (
          access_token or
          env.get('MapboxAccessToken') or
          env.get('MAPBOX_ACCESS_TOKEN'))
      session = requests.Session()
      session.params.update(access_token=access_token)
      session.headers.update({
          'User-Agent': 'mapbox-sdk-py/{0} {1}'.format(
              __version__, requests.utils.default_user_agent())})
      return session
docs: Create an HTTP session.
  
      Parameters
      ----------
      access_token : str
          Mapbox access token string (optional).
      env : dict, optional
          A dict that subsitutes for os.environ.
  
      Returns
      -------
      requests.Session