class_docstr: Galaxy simulation using the density wave theory 
docstr: x.__getitem__(y) <==> x[y] 
code: def __getitem__(self, key):
      """x.__getitem__(y) <==> x[y]"""
  
      if self._particles is not None:
          return self._particles[key]
      return None
  
file_path: vispy/examples/demo/gloo/galaxy/galaxy_simulation.py
imports: import math
  import numpy
label_desc: Use image node_id 3 for calling the Galaxy obj's underlying member method code with example usage: obj.__getitem__(key) and returns: None, self