Python poll api example

Some of the features described here may not be available in earlier versions of Python.

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Now available for Python 3! Buy the book! The module also includes polla Unix-only API, and several options that only work with specific variants of Unix. It monitors sockets, open files, and pipes anything with a fileno method that returns a valid file descriptor until they become readable or writable, or a communication error occurs. The echo server example from the socket section can be extended to watch for more than one connection at a time by using select. The arguments to select are three lists containing communication channels to monitor.

The first is a list of the objects to be checked for incoming data to be read, the second contains objects that will receive outgoing data when there is room in their buffer, and the third those that may have an error usually a combination of the input and output channel objects.

The next step in the server is to set up the lists containing input sources and output destinations to be passed to select. Connections are added to and removed from these lists by the server main loop.

Since this version of the server is going to wait for a socket to become writable before sending any data instead of immediately sending the replyeach output connection needs a queue to act as a buffer for the data to be sent through it. The main portion of the server program loops, calling select to block and wait for network activity. All of the sockets in the readable list have incoming data buffered and available to be read.

All of the sockets in the writable list have free space in their buffer and can be written to. In addition to adding the new connection to the list of inputs to monitor, this section sets the client socket to not block. The next case is an established connection with a client that has sent data. The data is read with recvthen placed on the queue so it can be sent through the socket and back to the client. A readable socket without data available is from a client that has disconnected, and the stream is ready to be closed.

There are fewer cases for the writable connections. If there is data in the queue for a connection, the next message is sent. Otherwise, the connection is removed from the list of output connections so that the next time through the loop select does not indicate that the socket is ready to send data.

The example client program uses two sockets to demonstrate how the server with select manages multiple connections at the same time. Then it sends one pieces of the message at a time via each socket, and reads all responses available after writing new data. Run the server in one window and the client in another. The output will look like this, with different port numbers.

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Using a timeout value lets a main program call select as part of a larger processing loop, taking other actions in between checking for network input.We use cookies to provide our services and for analytics and marketing. To find out more about our use of cookies, please see our Privacy Policy. By continuing to browse our website, you agree to our use of cookies.

With long-polling, the server delays the response to the client if there is no new data yet. This enables the server to respond instantly whenever the data does change.

Long-polling is a great way to dip your feet in the realtime waters without having to dramatically change your API contract and client code. Alright, so what kind of destruction do we need to do to your API contract?

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Hopefully not much at all. Fundamentally, you need a way for the client to make a conditional request for data. Queries against a timestamp are usually not good enough, as data could change twice with the same timestamp. Assuming your API has a good way to handle conditional requests, now you need to decide how the client should ask the server to delay a response.

It might be tempting to make the server automatically delay all requests that have failed conditionals.

python poll api example

However, this may break clients that depend on conditional checks responding quickly. We recommend making the long-polling behavior opt-in to be safe. For example:. This is saying the client wants a response from the server within 2 minutes.

On the client side, simply update any polling requests to ask for long-polling. The client code otherwise stays the same. Hopefully modifying your actual client code projects is just as easy. The real work is on the server side. You must be logged in to post a comment. You have clients repeatedly polling this API. Implementation, client side On the client side, simply update any polling requests to ask for long-polling. Implementation, server side The real work is on the server side.

First, install Pushpin and configure it to forward traffic to your backend. Comments There are no comments yet. Leave a comment Cancel reply You must be logged in to post a comment. As high as the polling interval e.The multiprocessing package offers both local and remote concurrency, effectively side-stepping the Global Interpreter Lock by using subprocesses instead of threads.

Due to this, the multiprocessing module allows the programmer to fully leverage multiple processors on a given machine. It runs on both Unix and Windows. The multiprocessing module also introduces APIs which do not have analogs in the threading module. A prime example of this is the Pool object which offers a convenient means of parallelizing the execution of a function across multiple input values, distributing the input data across processes data parallelism.

The following example demonstrates the common practice of defining such functions in a module so that child processes can successfully import that module. This basic example of data parallelism using Pool.

In multiprocessingprocesses are spawned by creating a Process object and then calling its start method. Process follows the API of threading. A trivial example of a multiprocess program is.

The Queue class is a near clone of Queue.

python poll api example

For example:. The Pipe function returns a pair of connection objects connected by a pipe which by default is duplex two-way. The two connection objects returned by Pipe represent the two ends of the pipe. Each connection object has send and recv methods among others.

Note that data in a pipe may become corrupted if two processes or threads try to read from or write to the same end of the pipe at the same time. Of course there is no risk of corruption from processes using different ends of the pipe at the same time. For instance one can use a lock to ensure that only one process prints to standard output at a time:.

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As mentioned above, when doing concurrent programming it is usually best to avoid using shared state as far as possible. This is particularly true when using multiple processes. However, if you really do need to use some shared data then multiprocessing provides a couple of ways of doing so.

Data can be stored in a shared memory map using Value or Array. For example, the following code. The 'd' and 'i' arguments used when creating num and arr are typecodes of the kind used by the array module: 'd' indicates a double precision float and 'i' indicates a signed integer.

These shared objects will be process and thread-safe. For more flexibility in using shared memory one can use the multiprocessing. A manager object returned by Manager controls a server process which holds Python objects and allows other processes to manipulate them using proxies. For example. Server process managers are more flexible than using shared memory objects because they can be made to support arbitrary object types.

Also, a single manager can be shared by processes on different computers over a network. They are, however, slower than using shared memory. The Pool class represents a pool of worker processes.

It has methods which allows tasks to be offloaded to the worker processes in a few different ways. This is covered in Programming guidelines however it is worth pointing out here. This means that some examples, such as the Pool examples will not work in the interactive interpreter.

If you try this it will actually output three full tracebacks interleaved in a semi-random fashion, and then you may have to stop the master process somehow.

The multiprocessing package mostly replicates the API of the threading module. Process objects represent activity that is run in a separate process. The Process class has equivalents of all the methods of threading.Indexing delay There is a delay from when an event is received by our servers until they are indexed and available via this endpoint. This is typically seconds, but can be up to 10 seconds.

For full documentation, see the Events API documentation. Create a new folder for this example open a command line console in this folder, run the following 3 lines:. Using your favorite editor, create a new file called poll-event-api. There might be cases where polling the API periodically might be preferred instead, such as: Integrating with legacy batch based APIs, where calling the API with one event at a time is too costly.

Integrating with an application behind a strict firewall, where opening the port needed for a Data Connector might not be possible. This article will cover some best practices when polling our events API and a code example. This is the span from which to fetch events. If these parameters are not set, it will default to fetching the last 24h. Also, from the API documentation: Indexing delay There is a delay from when an event is received by our servers until they are indexed and available via this endpoint.

Poll the Events API of all sensors at a fixed interval and print a summary to the console. Supports pagination of both devices, for large projects, and for events, for long intervals. Prerequisites To try out this code example you need to have Python 3 installed. Keep this console window open as we will use it to run the example in a moment. The source Using your favorite editor, create a new file called poll-event-api.

Run the code on the command line as follows: python.In this article, we will build a voting poll application that keeps track of each vote in a poll and broadcasts recent updates to all subscribed clients. We will be broadcasting the updates in realtime using Pusher and this will ensure that every connected user knows when a new vote has been made. There will also be an admin section that displays a chart.

This chart will update in realtime and show voting statistics. The top-left screen shows a browser window that loads the voting application and sends realtime updates. To show that these updates are propagated across every other connected client, we can see that the bottom-left screen also updates as a vote is cast on the former screen.

Finally, the admin screen by the right displays the chart and delivers realtime voting statistics. There is also a database that stores the status of votes of each poll member.

We will build the backend server for this application using a Python framework called Flask. We will use this framework to develop a simple backend API that can respond to the requests we will be sending from our JavaScript frontend. The source code for this tutorial is available here on GitHub. You will also need the following installed:.

Virtualenv is great for creating isolated Python environments, so we can install dependencies in an isolated environment, and not pollute our global packages directory.

Run the commands below:. Now that we have the virtual environment setup, we can install Flask within it with this command:. Before we do anything else, we need to install the Pusher library as we will need that for realtime updates. The first step will be to get a Pusher Channels application.

Polling the Events API

We will need the application credentials for our realtime features to work. Go to the Pusher website and create an account. After creating an account, you should create a new application. Follow the application creation wizard and then you should be given your application credentials, we will use this later in the article. We also need to install the Pusher Python Library to send events to Pusher. Install this using the command below:.By using our site, you acknowledge that you have read and understand our Cookie PolicyPrivacy Policyand our Terms of Service.

The dark mode beta is finally here. Change your preferences any time. Stack Overflow for Teams is a private, secure spot for you and your coworkers to find and share information. I am running a long process actually another python script in the background.

I need to know when it has finished. I have found that Popen. Is there another way to do this? Just run the command normally, then wait until Popen.

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I think you want either the popen. Communicate will grab the stdout and stderr data which you've put into PIPE. Of course these hold the main thread and wait for the other process to complete, which might be bad. If you want to busy wait then you could simply wrap your original code in a loop. Your original code did print "None" for me, btw. You shouldn't run your script with ampersand at the end. Because shell forks your process and returns 0 exit code.

Learn more. Python: Using popen poll on background process Ask Question. Asked 7 years, 7 months ago. Active 7 years, 7 months ago. Viewed 48k times. Rostyslav Dzinko Code Slinger Code Slinger 1 1 gold badge 1 1 silver badge 3 3 bronze badges. Active Oldest Votes. Popen ["sleep", "30"] Wait until process terminates while p. Popen [python. PIPE while p. Fedor Gogolev Fedor Gogolev 9, 2 2 gold badges 26 26 silver badges 34 34 bronze badges.

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It only takes a minute to sign up. I don't understand the issue of the context in the API, how do I know which is the correct context? See bpy. See Operator. Also see the Gotchas section of the API docs about that. By the way: You can pass an empty dict like bpy. You need to pass these members and repeat until it doesn't complain anymore.

But beware of certain operators, which require scene bases - if you don't provide a reference to them, Blender will crash to desktop before you even find out they are needed. Similar to the override, you need a 3D View instance, in this case its space data because this is the place where backgrounds reside.

Build a live polling web app with Python

The following code takes the first 3D View of the current screen layout if there's oneadds a new background and sets the image to an image datablock:. Sign up to join this community. The best answers are voted up and rise to the top. Home Questions Tags Users Unanswered. Asked 6 years, 3 months ago.

Active 1 year, 1 month ago. Viewed 22k times. CodeManX Jonathan Jonathan 1 1 gold badge 5 5 silver badges 3 3 bronze badges.

Active Oldest Votes. You can either: Run an operator via spacebar menu see bottom of the section in Blender 2. Change Area. Would you mind providing an example? Sign up or log in Sign up using Google.

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python poll api example

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