Rate limiting a web crawler

[Terry Reedy]

On 12/26/2018 10:35 AM, Simon Connah wrote:
> Hi,
> 
> I want to build a simple web crawler. I know how I am going to do it but 
> I have one problem.
> 
> Obviously I don't want to negatively impact any of the websites that I 
> am crawling so I want to implement some form of rate limiting of HTTP 
> requests to specific domain names.
> 
> What I'd like is some form of timer which calls a piece of code say 
> every 5 seconds or something and that code is what goes off and crawls 
> the website.
> 
> I'm just not sure on the best way to call code based on a timer.
> 
> Could anyone offer some advice on the best way to do this? It will be 
> running on Linux and using the python-daemon library to run it as a 
> service and will be using at least Python 3.6.

You can use asyncio to make repeated non-blocking requests to a web site 
at timed intervals and to work with multiple websites at once.  You can 
do the same with tkinter except that requests would block until a 
response unless you implemented your own polling.

-- 
Terry Jan Reedy