Resource not releasing in Simpy - what am I doing wrong?

Question

I have simplified the code representing the problem as suggested and attempted to debug.

Here is the most simple version of the code which still contains the bug:

import simpy

SIM_TIME = 5

def source(env):    
    i = 0
    while True:
        i += 1
        env.process(train(env, 'Train %d' % i, 'a'))
        yield env.timeout(1)
        i += 1
        env.process(train(env, 'Train %d' % i, 'b'))
        yield env.timeout(1)

def train(env, name, route):
    resource_req = resource.request()
    p3_req = p3.request()

    if route == 'a':
        print 'Route a %s generated' % name
        yield resource_req
        print 'Route a %s seized resource at time %d' % (name, env.now)
        yield env.timeout(1)
        resource.release(resource_req) 
        print 'Route a %s released resource at time %d' % (name, env.now)

    elif route == 'b':
        print 'Route b %s generated' % name
        yield p3_req
        print 'Route b %s seized resource at time %d' % (name, env.now)
        yield env.timeout(1)
        p3.release(p3_req)
        print 'Route b %s released resource at time %d' % (name, env.now)

    else:
        print 'Could not find a route branch'

env = simpy.Environment()

resource = simpy.Resource(env, 1)
p3 = simpy.Resource(env, 1)

env.process(source(env))
env.run(until=SIM_TIME)

The output from running this:

Route a Train 1 generated
Route a Train 1 seized resource at time 0
Route b Train 2 generated
Route a Train 1 released resource at time 1
Route a Train 3 generated
Route b Train 4 generated
Route a Train 5 generated

As you can see the resource is apparently released on "route a" but then no other resources can be seized either on route a or route b.

I'm very confused by this. Any help would be much appreciated!

Answer 1

Solved - there was a typo in the resource.

Originally defined as:

resource = simpy.Resource(env, 1)

Correct definition:

resource = simpy.Resource(env, capacity = 1)