packtpublishing / learning-concurrency-in-python

Learning Concurrency in Python by Packt

Learning Concurrency in Python

This is the code repository for Learning Concurrency in Python, published by Packt. It contains all the supporting project files necessary to work through the book from start to finish.

About the Book

Python is a very high level, general purpose language that is utilized heavily in fields such as data science and research, as well as being one of the top choices for general purpose programming for programmers around the world. It features a wide number of powerful, high and low-level libraries and frameworks that complement its delightful syntax and enable Python programmers to create.

Instructions and Navigation

All of the code is organized into folders. Each folder starts with a number followed by the application name. For example, Chapter02.

The code will look like the following:

import urllib.request
import time
t0 = time.time()
req = urllib.request.urlopen('http://www.example.com')
pageHtml = req.read()
t1 = time.time()
print("Total Time To Fetch Page: {} Seconds".format(t1-t0))

For this book, you will need the following software installed on your systems:

Beautiful Soup RxPy Anaconda Theano PyOpenCL

Related Products

• Learn Python in 7 Days

• Learning Concurrent Programming in Scala - Second Edition

• Learning Concurrent Programming in Scala

Download a free PDF

If you have already purchased a print or Kindle version of this book, you can get a DRM-free PDF version at no cost.
Simply click on the link to claim your free PDF.

https://packt.link/free-ebook/9781787285378

learning-concurrency-in-python's Issues

decoratorSet.py - NameError: name 'elem' is not defined

elem is used but not defined (in add and remove method).

Learning-Concurrency-in-Python/Chapter 05/decoratorSet.py

Line 15 in cd3f31b

return super(DecoratorLockedSet, self).add(elem)

Chapter 5 - webCrawler.py not working properly

I think this code is not working properly.
The result is very dependent on the number of threads you start.
The more threads you start, the more pages will be crawled.
I guess the problem is that the crawler threads finish due to empty queue and don't get back to work when there is new work in the queue.

Some results shown by the crawler when crawling https://tutorialedge.net

1 Thread: Total Number of Pages Visited 35
5 Threads: Total Number of Pages Visited 35
10 Threads: Total Number of Pages Visited 36
50 Threads: Total Number of Pages Visited 67
100 Threads: Total Number of Pages Visited 78

fullQueue.py - NameError: name 'mySubscriber' is not defined

Wrong name used.
Should be myPublisher.

Learning-Concurrency-in-Python/Chapter 05/fullQueue.py

Line 17 in cd3f31b

thread = threading.Thread(target=mySubscriber, args=(myQueue,))

LockedSet.__contains__ returns wrong value

The code in Chapter 5 - lockedSet.py doesn't work propperly.

If you create a LockedSet object i.e.

z = LockedSet({1, 2, 3, 4})

and check if 2 is in z it will fail.
2 in z
returns
False
z.__contains__(2)
returns
None

The solution is to return the result of super(LockedSet, self).__contains__(elem)

def __contains__(self, elem):
     with self._lock:`
          return super(LockedSet, self).__contains__(elem)

Learning-Concurrency-in-Python/Chapter 05/lockSet.py

Line 16 in cd3f31b

def __contains__(self, elem):

pubSub.py in Chapter 04 variable issue

In main() function there are no consumer1 and consumer2 declared but used.

def main():
  integers = []
  condition = threading.Condition()

  # Our Publisher
  pub1 = Publisher(integers, condition)
  pub1.start()

  # Our Subscribers
  sub1 = Subscriber(integers, condition)
  sub2 = Subscriber(integers, condition)
  sub1.start()
  sub2.start()

  ## Joining our Threads
  pub1.join()
  consumer1.join()
  consumer2.join()

Will send PR for this.

Chapter 1. rxPySample.py doesnt work - i fixed it

As rx library has updated the code should be:
import rx

class temperatureObserver():

def on_next(self, x):
print("Temperature is: %s degrees centigrade" % x)
if (x > 6):
print("Warning: Temperate Is Exceeding Recommended Limit")
if (x == 9):
print("DataCenter is shutting down. Temperature is too high")
def on_error(self, e):
print("Error: %s" % e)

def on_completed(self):
print("All Temps Read")

xs = rx.from_iterable(range(10))
d = xs.subscribe(temperatureObserver())

Chapter 2. ioBottleneck2.py doesnt work - i fixed it.

for python3 use:
import urllib.request
import time
from bs4 import BeautifulSoup

linkArray = []
def getLinks():
req = urllib.request.urlopen('http://www.example.com')
soup = BeautifulSoup(req.read(),features="lxml")
for link in soup.findAll('a'):
linkArray.append(link.get('href'))
print(len(linkArray))

getLinks()

Chapter 5. Problems with queue implementations

Details here: https://stackoverflow.com/questions/70468810/problems-with-multithreading-queues-implementations