Rate limiting function calls with Python Decorators

rateLimitDecorator.py

import time

def RateLimited(maxPerSecond):
    minInterval = 1.0 / float(maxPerSecond)
    def decorate(func):
        lastTimeCalled = [0.0]
        def rateLimitedFunction(*args,**kargs):
            elapsed = time.clock() - lastTimeCalled[0]
            leftToWait = minInterval - elapsed
            if leftToWait>0:
                time.sleep(leftToWait)
            ret = func(*args,**kargs)
            lastTimeCalled[0] = time.clock()
            return ret
        return rateLimitedFunction
    return decorate

@RateLimited(2)  # 2 per second at most
def PrintNumber(num):
    print num

if __name__ == "__main__":
    print "This should print 1,2,3... at about 2 per second."
    for i in range(1,100):
        PrintNumber(i)

Thanks team for sharing this. I've built a class for use in multiprocessing mode. Hope it helps others.

• I'm using time.time()
• Using multiprocessing instead of threading
• it's compatible with python 2.7 and 3.6

"""
    by oPromessa, 2017
    Published on https://github.com/oPromessa/flickr-uploader/

    Inspired by: https://gist.github.com/gregburek/1441055

    Helper class and functions to rate limiting function calls with Python Decorators

MIT License

Copyright (c) 2017 oPromessa

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all
copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
SOFTWARE.

"""

# ----------------------------------------------------------------------------
# Import section for Python 2 and 3 compatible code
# from __future__ import absolute_import, division, print_function, unicode_literals
from __future__ import division    # This way: 3 / 2 == 1.5; 3 // 2 == 1

# ----------------------------------------------------------------------------
# Import section
#
import sys
import logging
import multiprocessing
import time
from functools import wraps


# -----------------------------------------------------------------------------
# class LastTime to be used with rate_limited
#
class LastTime:
    """
        >>> import rate_limited as rt
        >>> a = rt.LastTime()
        >>> a.add_cnt()
        >>> a.get_cnt()
        1
        >>> a.add_cnt()
        >>> a.get_cnt()
        2
    """

    def __init__(self, name='LT'):
        # Init variables to None
        self.name = name
        self.ratelock = None
        self.cnt = None
        self.last_time_called = None

        # Instantiate control variables
        self.ratelock = multiprocessing.Lock()
        self.cnt = multiprocessing.Value('i', 0)
        self.last_time_called = multiprocessing.Value('d', 0.0)

        logging.debug('\t__init__: name=[{!s}]'.format(self.name))

    def acquire(self):
        self.ratelock.acquire()

    def release(self):
        self.ratelock.release()

    def set_last_time_called(self):
        self.last_time_called.value = time.time()
        # self.debug('set_last_time_called')

    def get_last_time_called(self):
        return self.last_time_called.value

    def add_cnt(self):
        self.cnt.value += 1

    def get_cnt(self):
        return self.cnt.value

    def debug(self, debugname='LT'):
        now=time.time()
        logging.debug('___Rate name:[{!s}] '
                      'debug=[{!s}] '
                      '\n\t        cnt:[{!s}] '
                      '\n\tlast_called:{!s} '
                      '\n\t  timenow():{!s} '
                      .format(self.name,
                              debugname,
                              self.cnt.value,
                              time.strftime(
                                '%T.{}'
                                .format(str(self.last_time_called.value -
                                            int(self.last_time_called.value))
                                            .split('.')[1][:3]),
                                time.localtime(self.last_time_called.value)),
                              time.strftime(
                                '%T.{}'
                                .format(str(now -
                                            int(now))
                                            .split('.')[1][:3]),
                                time.localtime(now))))


# -----------------------------------------------------------------------------
# rate_limited
#
# retries execution of a function
def rate_limited(max_per_second):

    min_interval = 1.0 / max_per_second
    LT = LastTime('rate_limited')

    def decorate(func):
        LT.acquire()
        if LT.get_last_time_called() == 0:
            LT.set_last_time_called()
        LT.debug('DECORATE')
        LT.release()

        @wraps(func)
        def rate_limited_function(*args, **kwargs):

            logging.warning('___Rate_limited f():[{!s}]: '
                            'Max_per_Second:[{!s}]'
                            .format(func.__name__, max_per_second))

            try:
                LT.acquire()
                LT.add_cnt()
                xfrom = time.time()

                elapsed = xfrom - LT.get_last_time_called()
                left_to_wait = min_interval - elapsed
                logging.debug('___Rate f():[{!s}] '
                              'cnt:[{!s}] '
                              '\n\tlast_called:{!s} '
                              '\n\t time now():{!s} '
                              'elapsed:{:6.2f} '
                              'min:{!s} '
                              'to_wait:{:6.2f}'
                              .format(func.__name__,
                                      LT.get_cnt(),
                                      time.strftime(
                                            '%T',
                                            time.localtime(
                                                LT.get_last_time_called())),
                                      time.strftime('%T',
                                                    time.localtime(xfrom)),
                                      elapsed,
                                      min_interval,
                                      left_to_wait))
                if left_to_wait > 0:
                    time.sleep(left_to_wait)

                ret = func(*args, **kwargs)

                LT.debug('OVER')
                LT.set_last_time_called()
                LT.debug('NEXT')

            except Exception as ex:
                # CODING: To be changed once reportError is on a module
                sys.stderr.write('+++000 '
                                 'Exception on rate_limited_function: [{!s}]\n'
                                 .format(ex))
                sys.stderr.flush()
                # reportError(Caught=True,
                #              CaughtPrefix='+++',
                #              CaughtCode='000',
                #              CaughtMsg='Exception on rate_limited_function',
                #              exceptUse=True,
                #              # exceptCode=ex.code,
                #              exceptMsg=ex,
                #              NicePrint=False,
                #              exceptSysInfo=True)
                raise
            finally:
                LT.release()
            return ret

        return rate_limited_function

    return decorate
# -----------------------------------------------------------------------------
# Samples
#@rate_limited(5) # 5 calls per second
# def print_num(num):
#     print (num )


# -----------------------------------------------------------------------------
# If called directly run doctests
#
if __name__ == "__main__":

    logging.basicConfig(level=logging.DEBUG,
                        format='[%(asctime)s]:[%(processName)-11s]' +
                               '[%(levelname)-8s]:[%(name)s] %(message)s')

    import doctest
    doctest.testmod()

    # Comment following line to allow further debugging/testing
    # sys.exit(0)

    # n for n calls per second  (ex. 3 means 3 calls per second)
    # 1/n for n seconds per call (ex. 0.5 meand 4 seconds in between calls)
    @rate_limited(1)
    def print_num(prc, num):
        """
        """
        print('\t\t***prc:[{!s}] num:[{!s}] '
              'rate_limit timestamp:[{!s}]'
              .format(prc, num, time.strftime('%T')))

    print('-------------------------------------------------Single Processing')
    for process in range(1, 3):
        for j in range(1, 2):
            print_num(process, j)

    print('-------------------------------------------------Multi Processing')
    def fmulti(x, prc):
        import random

        for i in range(1,x):
            r = random.randrange(6)
            print('\t\t[prc:{!s}] [{!s}]'
                  '->- WORKing {!s}s----[{!s}]'
                  .format(prc, i, r, time.strftime('%T')))
            time.sleep(r)
            print('\t\t[prc:{!s}] [{!s}]--> Before:---[{!s}]'
                  .format(prc, i, time.strftime('%T')))
            print_num(prc, i)
            print('\t\t[prc:{!s}] [{!s}]<-- After----[{!s}]'
                  .format(prc, i, time.strftime('%T')))

    TaskPool = []

    for j in range(1,4):
        Task = multiprocessing.Process(target=fmulti, args=(5,j))
        TaskPool.append(Task)
        Task.start()

    for j in TaskPool:
        print('{!s}.is_alive = {!s}'.format(j.name, j.is_alive()))

    while (True):
        if not (any(multiprocessing.active_children())):
            print('===No active children Processes.')
            break
        for p in multiprocessing.active_children():
            print('==={!s}.is_alive = {!s}'.format(p.name, p.is_alive()))
            uploadTaskActive = p
        print('===Will wait for 60 on {!s}.is_alive = {!s}'
              .format(uploadTaskActive.name,
                      uploadTaskActive.is_alive()))
        uploadTaskActive.join(timeout=60)
        print('===Waited for 60s on {!s}.is_alive = {!s}'
              .format(uploadTaskActive.name,
                      uploadTaskActive.is_alive()))

    # Wait for join all jobs/tasks in the Process Pool
    # All should be done by now!
    for j in TaskPool:
        j.join()
        print('==={!s} (is alive: {!s}).exitcode = {!s}'
              .format(j.name, j.is_alive(), j.exitcode))

@oPromessa thanks for sharing and nice job on the logging and example.

Why dont you use a counter instead of a list. Each time the function is called, increment the counter by 1 and reset the counter to 0 when the second or minute has changed

Any updates regarding licensing of these pieces of code?

Note, there are other libraries on PyPI that do this, such as ratelimit

A more simple version but with async compatibility https://gist.github.com/hugokernel/c478d639849e1e772b1395a546100031

I created a similar asyncio version but using the token bucket algorithm for
max number of calls during/time interval which results in a maximum burst rate. it can be combined with the above rate limiter without burst rate..

https://gist.github.com/yeus/dff02dce88c6da9073425b5309f524dd

An extended version of @oPromessa 's utility. Thank you for sharing @oPromessa !

I added Python 3.12 generic type-hinting and support for recursive calls using an RLock:

from typing import Callable, cast
from functools import wraps
import threading
import time


def rate_limited[T, **P](max_per_second: int) -> Callable[[Callable[P, T]], Callable[P, T]]:

    def decorator(fn: Callable[P, T]) -> Callable[P, T]:

        lock = threading.RLock()
        min_interval = 1.0 / max_per_second
        last_time_called = 0.0

        @wraps(fn)
        def wrapper(*args: P.args, **kwargs: P.kwargs) -> T:
            with lock:
                nonlocal last_time_called
                elapsed = time.perf_counter() - last_time_called
                left_to_wait = min_interval - elapsed
                if left_to_wait > 0:
                    time.sleep(left_to_wait)

                last_time_called = time.perf_counter()
                return fn(*args, **kwargs)

        return cast(Callable[P, T], wrapper)

    return decorator