pifetcher 0.0.3.4

A scalable headless data fetching library written with python and message queue service to enable quickly and easily prasing web data in a distributive way.

pifetcher

A scalable headless data fetching library written with python and message queue service to enable quickly and easily parsing web data in a distributive way.

To install

pip install pifetcher

PYPI Link https://pypi.org/project/pifetcher/

dependencies:

• selenium
• BeautifulSoup4
• boto3 (optional but by default)
• ChromeDriver for chrome 76(by default)
• Chrome executable v 76(by default)

features:

• event-callback-based interaction between user defined logic and the pre-disigned fetch worker
• process works in batches, library user will be able to capture the event of a batch of works have been finished
• easy to use, only needs to inherit the FetchWorker class and implement the basic call back functions
• it's design to use message queue, enbles more than just one worker to perform data fetching in order to scale the application

how to use:

1. set up work queue component on the host computer(aws simple queue service by default), such as credentials, regions AWS BOTO3 initial set up docs

2. configure a fetcher by creating a field mapping config file, for example: create a mapping config file for fetching amazon.com item pricing data

{
    "price": {
        "type": "text",
        "selector": "#priceblock_ourprice",
        "attribute":".text"
    },
    "id": {
        "type": "text",
        "selector": "#ASIN",
        "attribute": "value"
    },
    "title": {
        "type": "text",
        "selector": "#productTitle",
        "attribute":".text"
    }
}

3. create a pifetcherConfig.json file, and add the fetcher mapping file that previously created to fetcher -> mappingConfigs with its name and file path

numWorksPerTime : defines the number of messages it try to fetch from the queue per work cycle pollingIntervalOnActive : time interval before fetching the next message when the worker status is active(meaning it fetched at least on message in the last worker cycle) pollingIntervalOnIdle : time interval before fetching the next message when the worker status is active(meaning it fetched no message in the last worker cycle)

{
    "browser":{
        "browser_options":["--window-size=1920,1080", "--disable-extensions", "--proxy-server='direct://'", "--proxy-bypass-list=*", "--start-maximized","--ignore-certificate-errors", "--headless"],
        "win-driver_path":"chromedriver-win-76.exe",
        "win-binary_location": "",
        "mac-driver_path":"chromedriver-mac-76",
        "mac-binary_location": ""

    },
    "queue":
    {
        "numWorksPerTime": 1,
        "queueType":"AWSSimpleQueueService",
        "queueName":"datafetch.fifo",
        "pollingIntervalOnActive": 0.2,
        "pollingIntervalOnIdle": 60
    },
    "logger":
    {
        "output":"console"
    },
    "fetcher":
    {
        "mappingConfigs":{
            "amazon":"amazon.json"
        }

    }
}

4. to use the fetcher worker

• import the fetcher worker class and config class

from pifetcher.core import Config
from pifetcher.core import FetchWorker

• load the pifetherConfig.json to the Config class

Config.use('pifetcherConfig.json')

• implement event function with your own logic on_save_result : this will be called when a data object has been successfully parsed on_empty_result_error: this will be called after parsing an empty object, you may want to stop/ pause the process to investigate the problem before continuing parsing on_batch_start: this will be called when the worker received a batch start signal , you may implement your logic of adding fetching tasks to the queue here on_batch_finish: this will be called when the worker received a batch finish signal example:

    def on_save_result(self, result, batch_id, work):
        print(result, batch_id, work)
    def on_empty_result_error(self):
        self.stop()
    def on_batch_start(self, batch_id):
        work = {}
        work['url'] = 'a amazon url'
        work['fetcherName'] = 'amazon'
        self.add_works([work])
    def on_batch_finish(self, batch_id):
        print(f"all works with the batchId {batch_id} have been processed")

5. Run the worker and, send a StartProcess Signal to the queue to start the process

• start the worker to receive and process works

tw = TestWorker()
tw.do_works()

• to send a start signal to the queue If you want to send out the start signal from one of the worker, you can call this function

tw.send_start_signal()

But if you want to start the batch process from another system, you can use the code below

    sqs = boto3.resource('sqs')
    queue = sqs.get_queue_by_name(QueueName='datafetch.fifo')
    content = {"type":"BatchStart","batchId": str(uuid.uuid4()),"content":{}}
    queue.send_message(MessageBody=json.dumps(content), MessageGroupId = "FetchWork", MessageDeduplicationId = str(time.time()).replace(".",""))

Command to exit all chromedriver in windows

taskkill /f /im chromedriver-win-76.exe

How to optimized the number of polls the worker has to send to the queue

When no message was fetched in a worker cycle, it would enter the idle state. Under the idle state, it's supposed to wait a longer time interval before trying to fetch the next message. This sleep interval is defined in the config file at the location:

        "pollingIntervalOnIdle": 60

After the worker received at least one mssage in a worker cycle, the worker status will be set as ACTIVE. Under this state, it's supposed to wait a shorter time interval before trying to fetch the next message. This sleep interval is defined in the config file at the location:

        "pollingIntervalOnActive": 0.2,

To do list items:

• fix browser driver issues
• simplify initial setup process

Completed items:

• use better strategy to reduce number of requests a worker has to send
• put all constants in config the config file (checked)
• complete the type conversions for different data types (checked)
• add message type (work initiation message type) (checked)
• logging (checked)
• data fetching with use of aws sqs