docstr: Use + or - to zoom in and out.
  
  The mouse wheel can be used to zoom, but some people don't have mouse
  wheels :)
docstr_tok: ["Use","+","or","-","to","zoom","in","and","out",".","The","mouse","wheel","can","be","used","to","zoom",",","but","some","people","do","n't","have","mouse","wheels",":",")"]
code: def on_key_press(self, event):
      """Use + or - to zoom in and out.
  
      The mouse wheel can be used to zoom, but some people don't have mouse
      wheels :)
  
      """
      if event.text == "+" or event.text == "=":
          self.zoom(0.9)
      elif event.text == "-":
          self.zoom(1 / 0.9)
      self.update()
  
file_path: vispy/examples/demo/gloo/mandelbrot_double.py
imports: from __future__ import division
  import numpy
  from vispy import app, gloo
label_desc: Use image node_id 9 for calling the Canvas obj's underlying member method code with example usage: obj.on_key_press(event) without return types