class_docstr: Galaxy simulation using the density wave theory 
docstr: Number of particles 
code: def __len__(self):
      """Number of particles"""
  
      if self._particles is not None:
          return len(self._particles)
      return 0
  
file_path: vispy/examples/demo/gloo/galaxy/galaxy_simulation.py
imports: import math
  import numpy
label_desc: Use image node_id 2 for calling the Galaxy obj's underlying member method code with example usage: obj.__len__() and returns: int, len