Welcome, guest | Sign In | My Account | Store | Cart
NOTE: Recipes have moved! Please visit GitHub.com/activestate/code for the current versions.

I really like the Python 2.5 generator extensions. I have cases where I want a generator to pass a reference to itself to another generator, or to store it in a queue etc. Here's how a generator can get its own handle.

Python, 41 lines
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
# sample generator coroutine getting access to its own handle

import functools

def coroutine(function):
    """
    decorator to create a generator coroutine 
    Note that except for the calll to 'send()', this comes from PEP 342
    """
    @functools.wraps(function)
    def wrapper(*args, **kw):
        generator = function(*args, **kw) 
        result = generator.next() # one to get ready
        result = generator.send(generator) # two to store our own handle   
        return generator        
    return wrapper

process_queue = list() # queue for some imaginary process

def factory():
    @coroutine
    def test_function():
        """a simple function to test the coroutine decorator"""
        this_generator = (yield "foop")
        process_queue.append(this_generator)
    
        # now pretend to do some real work
        while True:
            result = (yield 42)
    return test_function()

print "creating generator instance"    
factory()

print "obtaining instance from queue"
generator = process_queue.pop()

print "executing one step"
x = generator.send(None)

print "result =", x         

The real case is asynchronous socket (and file) I/O.

A 'pollster' coroutine maintains a dictionary of filenos and generator references. After calling poll(), for each fileno that is ready for I/O, the pollster retrieves the generator instance and calls send() with the event flags from poll().

Each I/O coroutine places its socket fileno and a reference to itself in the pollster dictionary when itinitiates an asynchronous I/O request. It then yields, waiting for the pollster to signal I/O ready.

1 comment

da.martian Kervin 9 years, 1 month ago  # | flag

I would be interested to see how you could use this to do Async I/O. Has anyone implemented this and have sample code?

Created by Doug Fort on Wed, 27 Sep 2006 (PSF)
Python recipes (4591)
Doug Fort's recipes (5)

Required Modules

Other Information and Tasks