Source Code for Module joy.safety

 1  """ 
 2  Python module joy.safety 
 3   
 4  Contains classes implementing the safety protocols enforced by JoyApp 
 5   
 6  Main classes: 
 7    SafetyError -- exception class for indicating safety violations 
 8    BatteryVoltage -- a safety check that uses get_voltage calls and 
 9      enforces a lower bound on voltage 
10  """ 
11  from loggit import progress 
12   
13 -class SafetyError( RuntimeError ): 
14    """ 
15    Error used to indicate termination because of an unsafe working 
16    condition being detected 
17    """ 
18    pass 
19   
20     
21 -class BatteryVoltage( object ): 
22    """ 
23    Concrete class managing battery safety via a collection of objects  
24    that support the get_voltage method. 
25    """ 
26 -  def __init__(self, vmin, sensors, pollRate = 1.0): 
27      self.sensors = sensors 
28      self.vmin = vmin 
29      self.last = 0,None 
30      self.rate = pollRate 
31      progress("BatteryVoltage will test V<%g every %g seconds" % (vmin,pollRate)) 
32     
33 -  def poll( self, now ): 
34      """Polls voltage sensors listed in self.sensors 
35      for voltage measurements at the rate specified by self.rate 
36       
37      If a measurement is ready, it is stored in self.last 
38      as a (time,voltage) pair, and this pair is returned. 
39       
40      Otherwise, returns (None,None) 
41       
42      If the voltage is below vmin -- raises a SafetyError 
43      """ 
44      if not self.sensors: 
45        return None,None 
46      t,v = self.last 
47      if now - t < self.rate: 
48        return None,None 
49      s = self.sensors.pop(0) 
50      v = s.get_voltage() 
51      self.sensors.append(s) 
52      self.last = now, v 
53      if v<self.vmin: 
54        msg = "DANGER: voltage %g is below %g -- shutting down" % (v,self.vmin) 
55        raise SafetyError(msg) 
56      ###progress("Voltage %g" % v ) 
57      return self.last 
58