Remove redundant testing option

The `dt` option was added when `time_fn` was not available to
initialize PID instances.

Now that `time_fn` allows the time function to be injected as a
dependency, the `dt` option is redundant. It could be kept around
for backward compatibility, but I'd personally remove it because
IMHO the simpler the code the better.

Author: gonzalo-bulnes

simple_pid/pid.py

@@ -100,25 +100,19 @@ def __init__(
         # Set initial state of the controller
         self._integral = _clamp(starting_output, output_limits)
 
-    def __call__(self, input_, dt=None):
+    def __call__(self, input_):
         """
         Update the PID controller.
 
         Call the PID controller with *input_* and calculate and return a control output if
         sample_time seconds has passed since the last update. If no new output is calculated,
         return the previous output instead (or None if no value has been calculated yet).
-
-        :param dt: If set, uses this value for timestep instead of real time. This can be used in
-            simulations when simulation time is different from real time.
         """
         if not self.auto_mode:
             return self._last_output
 
         now = self.time_fn()
-        if dt is None:
-            dt = now - self._last_time if (now - self._last_time) else PID.MIN_DT
-        elif dt <= 0:
-            raise ValueError('dt has negative value {}, must be positive'.format(dt))
+        dt = now - self._last_time if (now - self._last_time) else PID.MIN_DT
 
         if (
             self.sample_time is not None

simple_pid/pid.pyi

@@ -31,7 +31,7 @@ class PID(object):
         time_fn: Optional[Callable[[], float]] = ...,
         starting_output: float = ...,
     ) -> None: ...
-    def __call__(self, input_: float, dt: Optional[float] = ...) -> Optional[float]: ...
+    def __call__(self, input_: float) -> Optional[float]: ...
     def __repr__(self) -> str: ...
     @property
     def components(self) -> _Components: ...