Allow fps() to dynamically get FPS value without having to call stop()

imutils/video/fps.py

@@ -2,32 +2,71 @@
 import datetime
 
 class FPS:
-	def __init__(self):
-		# store the start time, end time, and total number of frames
-		# that were examined between the start and end intervals
-		self._start = None
-		self._end = None
-		self._numFrames = 0
-
-	def start(self):
-		# start the timer
-		self._start = datetime.datetime.now()
-		return self
-
-	def stop(self):
-		# stop the timer
-		self._end = datetime.datetime.now()
-
-	def update(self):
-		# increment the total number of frames examined during the
-		# start and end intervals
-		self._numFrames += 1
-
-	def elapsed(self):
-		# return the total number of seconds between the start and
-		# end interval
-		return (self._end - self._start).total_seconds()
-
-	def fps(self):
-		# compute the (approximate) frames per second
-		return self._numFrames / self.elapsed()
+    def __init__(self):
+        """
+        store the start time, end time, and total number of frames
+        that were examined between the start and end intervals
+        """
+        self._start = None
+        self._end = None
+        self._numFrames = 0
+        self._pause = False
+
+    def start(self):
+        """start the timer"""
+        self._start = datetime.datetime.now()
+        return self
+
+    def stop(self):
+        """stop the timer"""
+        self._end = datetime.datetime.now()
+        self._pause = True
+
+    def unpause(self, if_not_paused:str = None):
+        """
+        Unpause the stopped timer.
+
+        Parameters
+        ----------
+        if_not_paused : str, {None, 'restart', 'raise'} default = None
+            This parameter controls behaviour when the timer has not been
+            paused:
+            ``None``:
+                Do nothing.
+            ``'restart'``:
+                Restart both the timer and the frame counter from zero.
+            ``'raise'``:
+                Raise an error.
+        """
+        if self._pause:
+            self._start = datetime.datetime.now() - (self._end - self._start)
+            self._end = None
+            self._pause = False
+        elif if_not_paused == 'restart':
+            self._end = None
+            self._numFrames = 0
+            return self.start()
+        elif if_not_paused == 'raise':
+            raise ValueError('Timer has not been paused.')
+
+    def update(self):
+        """
+        increment the total number of frames examined during the
+        start and end intervals
+        """
+        if not self._pause:
+            self._numFrames += 1
+
+    def elapsed(self):
+        """
+        return the total number of seconds between the start and
+        end interval
+        """
+        if self._end is None:
+            return (datetime.datetime.now() - self._start).total_seconds()
+        else:
+            return (self._end - self._start).total_seconds()
+
+    def fps(self):
+        """compute the (approximate) frames per second"""
+        return self._numFrames / self.elapsed()