Add backoff.py.

voussoirkit/backoff.py

@@ -0,0 +1,88 @@
+'''
+The Backoff classes are intended to be used to control `time.sleep` with
+varying backoff strategies.
+
+Example:
+
+bo = backoff.Linear(m=1, b=1, max=30)
+while True:
+    try:
+        something()
+    except Exception:
+        time.sleep(bo.next())
+    else:
+        bo.reset()
+
+If you want to add random fuzziness to your sleeps, that should be done on the
+calling end. For example, `bo.next() + (random.random() - 0.5)`.
+'''
+class Backoff:
+    def __init__(self, max):
+        if max is None:
+            pass
+        elif max <= 0:
+            raise ValueError(f'max must be positive, not {max}.')
+        self.max = max
+
+    def next(self):
+        y = self._calc()
+        if self.max is not None:
+            y = min(y, self.max)
+        self.x += 1
+        return y
+
+    def rewind(self, steps):
+        self.x = max(0, self.x - steps)
+
+    def reset(self):
+        self.x = 0
+
+####################################################################################################
+
+class Exponential(Backoff):
+    '''
+    Exponential backoff produces next = (a**x) + b.
+    '''
+    def __init__(self, a, b, *, max):
+        super().__init__(max)
+        self.x = 0
+        self.a = a
+        self.b = b
+        self.max = max
+
+    def _calc(self):
+        return (self.a ** self.x) + self.b
+
+class Linear(Backoff):
+    '''
+    Linear backoff produces next = (m * x) + b.
+    '''
+    def __init__(self, m, b, *, max):
+        super().__init__(max)
+        self.x = 0
+        self.m = m
+        self.b = b
+        self.max = max
+
+    def _calc(self):
+        return (self.m * self.x) + self.b
+
+class Quadratic(Backoff):
+    '''
+    Quadratic backoff produces next = (a * x**2) + (b * x) + c.
+    '''
+    def __init__(self, a, b, c, *, max):
+        super().__init__(max)
+        self.x = 0
+        self.a = a
+        self.b = b
+        self.c = c
+        self.max = max
+
+    def _calc(self):
+        return (self.a * self.x**2) + (self.b * self.x) + self.c
+
+'''
+people are backing off
+you'll get used to it
+'''