Just noting that, in principle, the wheel zoom tool might be in some other location in the .tools list besides index 1. A generic way of querying for all the wheel zoom tools on a plot is:
In [6]: p.select(WheelZoomTool)
Out[6]: [WheelZoomTool(id='1019', ...)]
Or if you are sure there is only one of them:
In [7]: p.select_one(WheelZoomTool)
Out[7]: WheelZoomTool(id='1019', ...)