Gate valve class

Gate valves are children of the parent Valve class, as shown in the following code example:

# valve.py (part 8)
1  class Gate(Valve): 
2      """Open/closed valve.""" 
3      def read_position(self): 
4          """Identify the position of the valve.""" 
5          if self.position == 0: 
6              return "{name} is closed.".format(name=self.name) 
7          elif self.position == 100: 
8              return "{name} is open.".format(name=self.name) 
9          else:  # bad condition 
10              return "Warning! {name} is partially open.".format(name=self.name) 
11 
12      def turn_handle(self, new_position): 
13          """Change the status of the valve.""" 
14          if new_position == 0: 
15              self.close() 
16          elif new_position == 100: 
17              self.open() 
18          else:  # Shouldn't get here 
19              return "Warning: Invalid valve position." 

The Gate subclass inherits everything from the Valve parent class. The only new methods it provides are read_position() and turn_handle(). As a gate valve is either open or closed (it doesn't affect fluid flow until more than 70% closed), we only need to know whether the valve is fully open or closed. In addition, when operating the valve, we only need to open or close it, so turn_handle() only accepts those two values; all others result in an error.