adityaarakeri · September 19, 2019 17:14 · Sep 19, 2019
diff --git a/retry_decorator.py b/retry_decorator.py
@@ -0,0 +1,200 @@
+import time
+from functools import wraps
+
+
+def retry(ExceptionToCheck, tries=4, delay=3, backoff=2, logger=None):
+    """Retry calling the decorated function using an exponential backoff.
+
+    http://www.saltycrane.com/blog/2009/11/trying-out-retry-decorator-python/
+    original from: http://wiki.python.org/moin/PythonDecoratorLibrary#Retry
+
+    :param ExceptionToCheck: the exception to check. may be a tuple of
+        exceptions to check
+    :type ExceptionToCheck: Exception or tuple
+    :param tries: number of times to try (not retry) before giving up
+    :type tries: int
+    :param delay: initial delay between retries in seconds
+    :type delay: int
+    :param backoff: backoff multiplier e.g. value of 2 will double the delay
+        each retry
+    :type backoff: int
+    :param logger: logger to use. If None, print
+    :type logger: logging.Logger instance
+    """
+    def deco_retry(f):
+
+        @wraps(f)
+        def f_retry(*args, **kwargs):
+            mtries, mdelay = tries, delay
+            while mtries > 1:
+                try:
+                    return f(*args, **kwargs)
+                except ExceptionToCheck, e:
+                    msg = "%s, Retrying in %d seconds..." % (str(e), mdelay)
+                    if logger:
+                        logger.warning(msg)
+                    else:
+                        print msg
+                    time.sleep(mdelay)
+                    mtries -= 1
+                    mdelay *= backoff
+            return f(*args, **kwargs)
+
+        return f_retry  # true decorator
+
+    return deco_retry
+
+# USE CASES
+
+# 1 ALWAYS FAIL CASE
+@retry(Exception, tries=4)
+def test_fail(text):
+    raise Exception("Fail")
+
+test_fail("it works!")
+
+
+# 2 ALWAYS SUCCESS CASE
+@retry(Exception, tries=4)
+def test_success(text):
+    print "Success: ", text
+
+test_success("it works!")
+
+# 3 RANDOM FAIL CASE
+import random
+
+@retry(Exception, tries=4)
+def test_random(text):
+    x = random.random()
+    if x < 0.5:
+        raise Exception("Fail")
+    else:
+        print "Success: ", text
+
+test_random("it works!")
+
+# 4 MULTPIPLE EXCEPTIONS CASE
+import random
+
+@retry((NameError, IOError), tries=20, delay=1, backoff=1)
+def test_multiple_exceptions():
+    x = random.random()
+    if x < 0.40:
+        raise NameError("NameError")
+    elif x < 0.80:
+        raise IOError("IOError")
+    else:
+        raise KeyError("KeyError")
+
+test_multiple_exceptions()
+
+####################
+# UNIT TESTS
+
+import logging
+import unittest
+
+from decorators import retry
+
+
+class RetryableError(Exception):
+    pass
+
+
+class AnotherRetryableError(Exception):
+    pass
+
+
+class UnexpectedError(Exception):
+    pass
+
+
+class RetryTestCase(unittest.TestCase):
+
+    def test_no_retry_required(self):
+        self.counter = 0
+
+        @retry(RetryableError, tries=4, delay=0.1)
+        def succeeds():
+            self.counter += 1
+            return 'success'
+
+        r = succeeds()
+
+        self.assertEqual(r, 'success')
+        self.assertEqual(self.counter, 1)
+
+    def test_retries_once(self):
+        self.counter = 0
+
+        @retry(RetryableError, tries=4, delay=0.1)
+        def fails_once():
+            self.counter += 1
+            if self.counter < 2:
+                raise RetryableError('failed')
+            else:
+                return 'success'
+
+        r = fails_once()
+        self.assertEqual(r, 'success')
+        self.assertEqual(self.counter, 2)
+
+    def test_limit_is_reached(self):
+        self.counter = 0
+
+        @retry(RetryableError, tries=4, delay=0.1)
+        def always_fails():
+            self.counter += 1
+            raise RetryableError('failed')
+
+        with self.assertRaises(RetryableError):
+            always_fails()
+        self.assertEqual(self.counter, 4)
+
+    def test_multiple_exception_types(self):
+        self.counter = 0
+
+        @retry((RetryableError, AnotherRetryableError), tries=4, delay=0.1)
+        def raise_multiple_exceptions():
+            self.counter += 1
+            if self.counter == 1:
+                raise RetryableError('a retryable error')
+            elif self.counter == 2:
+                raise AnotherRetryableError('another retryable error')
+            else:
+                return 'success'
+
+        r = raise_multiple_exceptions()
+        self.assertEqual(r, 'success')
+        self.assertEqual(self.counter, 3)
+
+    def test_unexpected_exception_does_not_retry(self):
+
+        @retry(RetryableError, tries=4, delay=0.1)
+        def raise_unexpected_error():
+            raise UnexpectedError('unexpected error')
+
+        with self.assertRaises(UnexpectedError):
+            raise_unexpected_error()
+
+    def test_using_a_logger(self):
+        self.counter = 0
+
+        sh = logging.StreamHandler()
+        logger = logging.getLogger(__name__)
+        logger.addHandler(sh)
+
+        @retry(RetryableError, tries=4, delay=0.1, logger=logger)
+        def fails_once():
+            self.counter += 1
+            if self.counter < 2:
+                raise RetryableError('failed')
+            else:
+                return 'success'
+
+        fails_once()
+
+
+if __name__ == '__main__':
+    unittest.main()