Function decorator to limit calls to the function to a given rate.

ratelimit.py

"""Limit calls to a function to a given rate.

Intended for use with functions that interact with systems not under the
programmers control (for example, downloading html content from servers
for parsing).

usage:
    
    # Two rate limited functions
    # One limited to the default 3 second delay.
    @ratelimit()
    def limited_3s():
        pass
    
    # The second limited to a 1 second delay.
    @ratelimit(1.0)
    def limited_1s():
        pass
    
    # Tie two functions to the same limiter.
    # Calling these functions sequentially will result in a 3 second
    # delay between them.
    limiter = ratelimit()
    
    @limiter
    def tiedlimit1(): pass
    
    @limiter
    def tiedlimit2(): pass

Copyright (c) 2011 Erik Youngren

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 time

class ratelimit:
    """Limits the decorated functions to a given call rate.
    
    By default, this limit is once every 3 seconds (first call is
    unhindered), and checks the time every 0.5 seconds.
    
    Execution is blocked during this delay. Patches to support
    asynchronous are welcome.
    
    """
    def __init__(self, delay=3.0, interval=0.5):
        self.delay = delay
        self.interval = interval
        self.last_call = 0.0
    
    def __call__(self, func):
        def wrapper(*args, **kwargs):
            while time.time() - self.last_call < self.delay:
                time.sleep(self.interval)
            
            self.last_call = time.time()
            
            func(*args, **kwargs)
        
        return wrapper


def main():
    limiter = ratelimit(1.0)
    
    @limiter
    def x(): print('x')
    
    @limiter
    def y(): print('y')
    
    for i in range(2):
        x()
        y()

if __name__ == "__main__":
    main()