Semalt Review – Running A Scraping Script

1. 23.05.2018 Semalt Review – Running A Scraping Script Air?ow is a scheduler libraries for Python used to con?gure multi-system work?ows executed in parallel across any number of users. A single Air?ow pipeline comprises of SQL, bash, and Python operations. The tool works by specifying on dependencies between tasks, a critical element that helps determine the tasks to be run in parallel and which ones to be executed after the other functions are complete. Why Air?ow? Air?ow tool is written in Python, giving you the advantage to add your operators to the already set custom functionality. This tool allows you to scrape data through transformations from a website to a well-structured datasheet. Air?ow uses Directed Acyclic Graphs (DAG) to represent a speci?c work?ow. In this case, a work?ow refers to a collection of tasks that comprises of directional dependencies. How Apache Air?ow works http://rankexperience.com/articles/article2437.html 1/3

2. 23.05.2018 Air?ow is a Warehouse Management System that works to de?ne tasks as their ultimate dependencies as the code executes the functions on a schedule and distributes the task execution across all the worker processes. This tool offers a user interface that displays the state of both running and past tasks. Air?ow displays diagnostic information to users regarding the task execution process and allows the end-user to manage execution of tasks manually. Note that a directed acyclic graph is only used to set the execution context and to organize tasks. In Air?ow, tasks are the crucial elements that run a scraping script. In scraping, tasks comprise of two ?avors that include: Operator In some cases, tasks work as operators where they execute operations as speci?ed by the end users. Operators are designed to run scraping script and other functions that can be performed in Python programming language. Sensor Tasks are also developed to work as sensors. In such a case, execution of tasks that depend on each other can be paused until a criterion where a work?ow runs smoothly has been met. Air?ow is used in different ?elds to run a scraping script. Below is a guide on how to use Air?ow. Open your browser and check your user interface Check the work?ow that failed and clicks on it to see the tasks that went wrong Click on "View log" to check the cause of failure. In many cases, password authentication failure causes the work?ow failure Go to the admin section and click on "Connections." Edit the Postgres connection to retrieve the new password and click "Save." Re-visit your browser and click on the task that had failed. Click on the task and tap "Clear" so that the task runs successfully next time. Other Python schedulers to consider Cron Cron Cron is a Unix-based OS used to run scraping scripts periodically at ?xed intervals, dates, and times. This library is mostly used to maintain and set up software environments. Luigi Luigi http://rankexperience.com/articles/article2437.html 2/3

3. 23.05.2018 Luigi is a Python module that will allow you to handle visualization and dependency resolution. Luigi is used for creating complex pipelines of jobs collection. Air?ow is a scheduler library for Python used to handle dependency management projects. In Air?ow, running tasks depends on each other. To obtain consistent results, you can set your Air?ow script to run automatically after every an hour or two. http://rankexperience.com/articles/article2437.html 3/3