[arvados] created: 2.1.0-3066-gbb406742b
git repository hosting
git at public.arvados.org
Mon Nov 21 15:39:23 UTC 2022
at bb406742b50b90d3796ec86c4c7f806004cc3933 (commit)
commit bb406742b50b90d3796ec86c4c7f806004cc3933
Author: Brett Smith <brett.smith at curii.com>
Date: Thu Nov 10 16:58:21 2022 -0500
18797: Update style of arvados.retry docstrings.
I wrote these docstrings as a demonstration of new style rules for our
Python SDK. It is real, useful documentation, as well as a good
illustration of how to follow the new style guide, so we might as well
merge it.
This is primarily a style update to the existing docstrings. In places
where I've actually changed the meaning, I believe the new meaning is
more correct. In particular, RetryLoop's "attempts" count the number of
saved results, which may or may not be the same as the number of times
the loop has run depending on what the body does.
Arvados-DCO-1.1-Signed-off-by: Brett Smith <brett.smith at curii.com>
diff --git a/sdk/python/arvados/retry.py b/sdk/python/arvados/retry.py
index ea4095930..e93624a5d 100644
--- a/sdk/python/arvados/retry.py
+++ b/sdk/python/arvados/retry.py
@@ -1,3 +1,16 @@
+"""Utilities to retry operations.
+
+The core of this module is `RetryLoop`, a utility class to retry operations
+that might fail. It can distinguish between temporary and permanent failures;
+provide exponential backoff; and save a series of results.
+
+It also provides utility functions for common operations with `RetryLoop`:
+
+* `check_http_response_success` can be used as a `RetryLoop` `success_check`
+ for HTTP response codes from the Arvados API server.
+* `retry_method` can decorate methods to provide a default `num_retries`
+ keyword argument.
+"""
# Copyright (C) The Arvados Authors. All rights reserved.
#
# SPDX-License-Identifier: Apache-2.0
@@ -19,7 +32,7 @@ _HTTP_CAN_RETRY = set([408, 409, 422, 423, 500, 502, 503, 504])
class RetryLoop(object):
"""Coordinate limited retries of code.
- RetryLoop coordinates a loop that runs until it records a
+ `RetryLoop` coordinates a loop that runs until it records a
successful result or tries too many times, whichever comes first.
Typical use looks like:
@@ -33,30 +46,41 @@ class RetryLoop(object):
loop.save_result(result)
if loop.success():
return loop.last_result()
+
+ Arguments:
+
+ num_retries: int
+ : The maximum number of times to retry the loop if it
+ doesn't succeed. This means the loop body could run at most
+ `num_retries + 1` times.
+
+ success_check: Callable
+ : This is a function that will be called each
+ time the loop saves a result. The function should return
+ `True` if the result indicates the code succeeded, `False` if it
+ represents a permanent failure, and `None` if it represents a
+ temporary failure. If no function is provided, the loop will
+ end after any result is saved.
+
+ backoff_start: float
+ : The number of seconds that must pass before the loop's second
+ iteration. Default 0, which disables all waiting.
+
+ backoff_growth: float
+ : The wait time multiplier after each iteration.
+ Default 2 (i.e., double the wait time each time).
+
+ save_results: int
+ : Specify a number to store that many saved results from the loop.
+ These are available through the `results` attribute, oldest first.
+ Default 1.
+
+ max_wait: float
+ : Maximum number of seconds to wait between retries. Default 60.
"""
def __init__(self, num_retries, success_check=lambda r: True,
backoff_start=0, backoff_growth=2, save_results=1,
max_wait=60):
- """Construct a new RetryLoop.
-
- Arguments:
- * num_retries: The maximum number of times to retry the loop if it
- doesn't succeed. This means the loop could run at most 1+N times.
- * success_check: This is a function that will be called each
- time the loop saves a result. The function should return
- True if the result indicates loop success, False if it
- represents a permanent failure state, and None if the loop
- should continue. If no function is provided, the loop will
- end as soon as it records any result.
- * backoff_start: The number of seconds that must pass before the
- loop's second iteration. Default 0, which disables all waiting.
- * backoff_growth: The wait time multiplier after each iteration.
- Default 2 (i.e., double the wait time each time).
- * save_results: Specify a number to save the last N results
- that the loop recorded. These records are available through
- the results attribute, oldest first. Default 1.
- * max_wait: Maximum number of seconds to wait between retries.
- """
self.tries_left = num_retries + 1
self.check_result = success_check
self.backoff_wait = backoff_start
@@ -69,12 +93,24 @@ class RetryLoop(object):
self._success = None
def __iter__(self):
+ """Return an iterator of retries."""
return self
def running(self):
+ """Return whether this loop is running.
+
+ Returns `None` if the loop has never run, `True` if it is still running,
+ or `False` if it has stopped—whether that's because it has saved a
+ successful result, a permanent failure, or has run out of retries.
+ """
return self._running and (self._success is None)
def __next__(self):
+ """Record a loop attempt.
+
+ If the loop is still running, decrements the number of tries left and
+ returns it. Otherwise, raises `StopIteration`.
+ """
if self._running is None:
self._running = True
if (self.tries_left < 1) or not self.running():
@@ -94,8 +130,16 @@ class RetryLoop(object):
"""Record a loop result.
Save the given result, and end the loop if it indicates
- success or permanent failure. See __init__'s documentation
- about success_check to learn how to make that indication.
+ success or permanent failure. See documentation for the `__init__`
+ `success_check` argument to learn how that's indicated.
+
+ Raises `arvados.errors.AssertionError` if called after the loop has
+ already ended.
+
+ Arguments:
+
+ result: Any
+ : The result from this loop attempt to check and save.
"""
if not self.running():
raise arvados.errors.AssertionError(
@@ -107,13 +151,17 @@ class RetryLoop(object):
def success(self):
"""Return the loop's end state.
- Returns True if the loop obtained a successful result, False if it
- encountered permanent failure, or else None.
+ Returns `True` if the loop recorded a successful result, `False` if it
+ recorded permanent failure, or else `None`.
"""
return self._success
def last_result(self):
- """Return the most recent result the loop recorded."""
+ """Return the most recent result the loop saved.
+
+ Raises `arvados.errors.AssertionError` if called before any result has
+ been saved.
+ """
try:
return self.results[-1]
except IndexError:
@@ -121,13 +169,19 @@ class RetryLoop(object):
"queried loop results before any were recorded")
def attempts(self):
- """Return the number of attempts that have been made.
+ """Return the number of results that have been saved.
- Includes successes and failures."""
+ This count includes all kinds of results: success, permanent failure,
+ and temporary failure.
+ """
return self._attempts
def attempts_str(self):
- """Human-readable attempts(): 'N attempts' or '1 attempt'"""
+ """Return a human-friendly string counting saved results.
+
+ This method returns '1 attempt' or 'N attempts', where the number
+ in the string is the number of saved results.
+ """
if self._attempts == 1:
return '1 attempt'
else:
@@ -135,23 +189,30 @@ class RetryLoop(object):
def check_http_response_success(status_code):
- """Convert an HTTP status code to a loop control flag.
+ """Convert a numeric HTTP status code to a loop control flag.
- Pass this method a numeric HTTP status code. It returns True if
- the code indicates success, None if it indicates temporary
- failure, and False otherwise. You can use this as the
- success_check for a RetryLoop.
+ This method takes a numeric HTTP status code and returns `True` if
+ the code indicates success, `None` if it indicates temporary
+ failure, and `False` otherwise. You can use this as the
+ `success_check` for a `RetryLoop` that queries the Arvados API server.
+ Specifically:
- Implementation details:
- * Any 2xx result returns True.
- * A select few status codes, or any malformed responses, return None.
+ * Any 2xx result returns `True`.
+
+ * A select few status codes, or any malformed responses, return `None`.
422 Unprocessable Entity is in this category. This may not meet the
letter of the HTTP specification, but the Arvados API server will
use it for various server-side problems like database connection
errors.
- * Everything else returns False. Note that this includes 1xx and
+
+ * Everything else returns `False`. Note that this includes 1xx and
3xx status codes. They don't indicate success, and you can't
retry those requests verbatim.
+
+ Arguments:
+
+ status_code: int
+ : A numeric HTTP response code
"""
if status_code in _HTTP_SUCCESSES:
return True
@@ -166,9 +227,14 @@ def retry_method(orig_func):
"""Provide a default value for a method's num_retries argument.
This is a decorator for instance and class methods that accept a
- num_retries argument, with a None default. When the method is called
- without a value for num_retries, it will be set from the underlying
- instance or class' num_retries attribute.
+ `num_retries` keyword argument, with a `None` default. When the method
+ is called without a value for `num_retries`, this decorator will set it
+ from the `num_retries` attribute of the underlying instance or class.
+
+ Arguments:
+
+ orig_func: Callable
+ : A class or instance method that accepts a `num_retries` keyword argument
"""
@functools.wraps(orig_func)
def num_retries_setter(self, *args, **kwargs):
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