Extensions

Extensions are components that allow inserting your own custom functionality into Scrapy.

Unlike other components, extensions do not have a specific role in Scrapy. They are “wildcard” components that can be used for anything that does not fit the role of any other type of component.

Loading and activating extensions

Extensions are loaded at startup by creating a single instance of the extension class per spider being run.

To enable an extension, add it to the EXTENSIONS setting. For example:

EXTENSIONS = {
    "scrapy.extensions.corestats.CoreStats": 500,
    "scrapy.extensions.telnet.TelnetConsole": 500,
}

EXTENSIONS is merged with EXTENSIONS_BASE (not meant to be overridden), and the priorities in the resulting value determine the loading order.

As extensions typically do not depend on each other, their loading order is irrelevant in most cases. This is why the EXTENSIONS_BASE setting defines all extensions with the same order (0). However, you may need to carefully use priorities if you add an extension that depends on other extensions being already loaded.

Writing your own extension

Each extension is a component.

Typically, extensions connect to signals and perform tasks triggered by them.

Sample extension

Here we will implement a simple extension to illustrate the concepts described in the previous section. This extension will log a message every time:

a spider is opened
a spider is closed
a specific number of items are scraped

The extension will be enabled through the MYEXT_ENABLED setting and the number of items will be specified through the MYEXT_ITEMCOUNT setting.

Here is the code of such extension:

import logging
from scrapy import signals
from scrapy.exceptions import NotConfigured

logger = logging.getLogger(__name__)


class SpiderOpenCloseLogging:
    def __init__(self, item_count):
        self.item_count = item_count
        self.items_scraped = 0

    @classmethod
    def from_crawler(cls, crawler):
        # first check if the extension should be enabled and raise
        # NotConfigured otherwise
        if not crawler.settings.getbool("MYEXT_ENABLED"):
            raise NotConfigured

        # get the number of items from settings
        item_count = crawler.settings.getint("MYEXT_ITEMCOUNT", 1000)

        # instantiate the extension object
        ext = cls(item_count)

        # connect the extension object to signals
        crawler.signals.connect(ext.spider_opened, signal=signals.spider_opened)
        crawler.signals.connect(ext.spider_closed, signal=signals.spider_closed)
        crawler.signals.connect(ext.item_scraped, signal=signals.item_scraped)

        # return the extension object
        return ext

    def spider_opened(self, spider):
        logger.info("opened spider %s", spider.name)

    def spider_closed(self, spider):
        logger.info("closed spider %s", spider.name)

    def item_scraped(self, item, spider):
        self.items_scraped += 1
        if self.items_scraped % self.item_count == 0:
            logger.info("scraped %d items", self.items_scraped)

Built-in extensions reference

General purpose extensions

Log Stats extension

class scrapy.extensions.logstats.LogStats[source]

Log basic stats like crawled pages and scraped items.

Core Stats extension

class scrapy.extensions.corestats.CoreStats[source]

Enable the collection of core statistics, provided the stats collection is enabled (see Stats Collection).

Telnet console extension

class scrapy.extensions.telnet.TelnetConsole[source]

Provides a telnet console for getting into a Python interpreter inside the currently running Scrapy process, which can be very useful for debugging.

The telnet console must be enabled by the TELNETCONSOLE_ENABLED setting, and the server will listen in the port specified in TELNETCONSOLE_PORT.

Memory usage extension

class scrapy.extensions.memusage.MemoryUsage[source]

Note

This extension does not work in Windows.

Monitors the memory used by the Scrapy process that runs the spider and:

sends a notification e-mail when it exceeds a certain value
closes the spider when it exceeds a certain value

The notification e-mails can be triggered when a certain warning value is reached (MEMUSAGE_WARNING_MB) and when the maximum value is reached (MEMUSAGE_LIMIT_MB) which will also cause the spider to be closed and the Scrapy process to be terminated.

This extension is enabled by the MEMUSAGE_ENABLED setting and can be configured with the following settings:

Memory debugger extension

class scrapy.extensions.memdebug.MemoryDebugger[source]

An extension for debugging memory usage. It collects information about:

objects uncollected by the Python garbage collector
objects left alive that shouldn’t. For more info, see Debugging memory leaks with trackref

To enable this extension, turn on the MEMDEBUG_ENABLED setting. The info will be stored in the stats.

Spider state extension

class scrapy.extensions.spiderstate.SpiderState[source]

Manages spider state data by loading it before a crawl and saving it after.

Give a value to the JOBDIR setting to enable this extension. When enabled, this extension manages the state attribute of your Spider instance:

When your spider closes (spider_closed), the contents of its state attribute are serialized into a file named spider.state in the JOBDIR folder.
When your spider opens (spider_opened), if a previously-generated spider.state file exists in the JOBDIR folder, it is loaded into the state attribute.

For an example, see Keeping persistent state between batches.

Close spider extension

class scrapy.extensions.closespider.CloseSpider[source]

Closes a spider automatically when some conditions are met, using a specific closing reason for each condition.

The conditions for closing a spider can be configured through the following settings:

CLOSESPIDER_TIMEOUT
CLOSESPIDER_TIMEOUT_NO_ITEM
CLOSESPIDER_ITEMCOUNT
CLOSESPIDER_PAGECOUNT
CLOSESPIDER_ERRORCOUNT

Note

When a certain closing condition is met, requests which are currently in the downloader queue (up to CONCURRENT_REQUESTS requests) are still processed.

CLOSESPIDER_TIMEOUT

Default: 0

An integer which specifies a number of seconds. If the spider remains open for more than that number of second, it will be automatically closed with the reason closespider_timeout. If zero (or non set), spiders won’t be closed by timeout.

CLOSESPIDER_TIMEOUT_NO_ITEM

Default: 0

An integer which specifies a number of seconds. If the spider has not produced any items in the last number of seconds, it will be closed with the reason closespider_timeout_no_item. If zero (or non set), spiders won’t be closed regardless if it hasn’t produced any items.

CLOSESPIDER_ITEMCOUNT

Default: 0

An integer which specifies a number of items. If the spider scrapes more than that amount and those items are passed by the item pipeline, the spider will be closed with the reason closespider_itemcount. If zero (or non set), spiders won’t be closed by number of passed items.

CLOSESPIDER_PAGECOUNT

Default: 0

An integer which specifies the maximum number of responses to crawl. If the spider crawls more than that, the spider will be closed with the reason closespider_pagecount. If zero (or non set), spiders won’t be closed by number of crawled responses.

CLOSESPIDER_PAGECOUNT_NO_ITEM

Default: 0

An integer which specifies the maximum number of consecutive responses to crawl without items scraped. If the spider crawls more consecutive responses than that and no items are scraped in the meantime, the spider will be closed with the reason closespider_pagecount_no_item. If zero (or not set), spiders won’t be closed by number of crawled responses with no items.

CLOSESPIDER_ERRORCOUNT

Default: 0

An integer which specifies the maximum number of errors to receive before closing the spider. If the spider generates more than that number of errors, it will be closed with the reason closespider_errorcount. If zero (or non set), spiders won’t be closed by number of errors.

StatsMailer extension

class scrapy.extensions.statsmailer.StatsMailer[source]

This simple extension can be used to send a notification e-mail every time a domain has finished scraping, including the Scrapy stats collected. The email will be sent to all recipients specified in the STATSMAILER_RCPTS setting.

Emails can be sent using the MailSender class. To see a full list of parameters, including examples on how to instantiate MailSender and use mail settings, see Sending e-mail.

Periodic log extension

class scrapy.extensions.periodic_log.PeriodicLog[source]

This extension periodically logs rich stat data as a JSON object:

2023-08-04 02:30:57 [scrapy.extensions.logstats] INFO: Crawled 976 pages (at 162 pages/min), scraped 925 items (at 161 items/min)
2023-08-04 02:30:57 [scrapy.extensions.periodic_log] INFO: {
    "delta": {
        "downloader/request_bytes": 55582,
        "downloader/request_count": 162,
        "downloader/request_method_count/GET": 162,
        "downloader/response_bytes": 618133,
        "downloader/response_count": 162,
        "downloader/response_status_count/200": 162,
        "item_scraped_count": 161
    },
    "stats": {
        "downloader/request_bytes": 338243,
        "downloader/request_count": 992,
        "downloader/request_method_count/GET": 992,
        "downloader/response_bytes": 3836736,
        "downloader/response_count": 976,
        "downloader/response_status_count/200": 976,
        "item_scraped_count": 925,
        "log_count/INFO": 21,
        "log_count/WARNING": 1,
        "scheduler/dequeued": 992,
        "scheduler/dequeued/memory": 992,
        "scheduler/enqueued": 1050,
        "scheduler/enqueued/memory": 1050
    },
    "time": {
        "elapsed": 360.008903,
        "log_interval": 60.0,
        "log_interval_real": 60.006694,
        "start_time": "2023-08-03 23:24:57",
        "utcnow": "2023-08-03 23:30:57"
    }
}

This extension logs the following configurable sections:

"delta" shows how some numeric stats have changed since the last stats log message.

The PERIODIC_LOG_DELTA setting determines the target stats. They must have int or float values.
"stats" shows the current value of some stats.

The PERIODIC_LOG_STATS setting determines the target stats.
"time" shows detailed timing data.

The PERIODIC_LOG_TIMING_ENABLED setting determines whether or not to show this section.

This extension logs data at the start, then on a fixed time interval configurable through the LOGSTATS_INTERVAL setting, and finally right before the crawl ends.

Example extension configuration:

custom_settings = {
    "LOG_LEVEL": "INFO",
    "PERIODIC_LOG_STATS": {
        "include": ["downloader/", "scheduler/", "log_count/", "item_scraped_count/"],
    },
    "PERIODIC_LOG_DELTA": {"include": ["downloader/"]},
    "PERIODIC_LOG_TIMING_ENABLED": True,
    "EXTENSIONS": {
        "scrapy.extensions.periodic_log.PeriodicLog": 0,
    },
}

PERIODIC_LOG_DELTA

Default: None

"PERIODIC_LOG_DELTA": True - show deltas for all int and float stat values.
"PERIODIC_LOG_DELTA": {"include": ["downloader/", "scheduler/"]} - show deltas for stats with names containing any configured substring.
"PERIODIC_LOG_DELTA": {"exclude": ["downloader/"]} - show deltas for all stats with names not containing any configured substring.

PERIODIC_LOG_STATS

Default: None

"PERIODIC_LOG_STATS": True - show the current value of all stats.
"PERIODIC_LOG_STATS": {"include": ["downloader/", "scheduler/"]} - show current values for stats with names containing any configured substring.
"PERIODIC_LOG_STATS": {"exclude": ["downloader/"]} - show current values for all stats with names not containing any configured substring.

PERIODIC_LOG_TIMING_ENABLED

Default: False

True enables logging of timing data (i.e. the "time" section).

Debugging extensions

Stack trace dump extension

class scrapy.extensions.periodic_log.StackTraceDump

Dumps information about the running process when a SIGQUIT or SIGUSR2 signal is received. The information dumped is the following:

engine status (using scrapy.utils.engine.get_engine_status())
live references (see Debugging memory leaks with trackref)
stack trace of all threads

After the stack trace and engine status is dumped, the Scrapy process continues running normally.

This extension only works on POSIX-compliant platforms (i.e. not Windows), because the SIGQUIT and SIGUSR2 signals are not available on Windows.

There are at least two ways to send Scrapy the SIGQUIT signal:

By pressing Ctrl-while a Scrapy process is running (Linux only?)
By running this command (assuming <pid> is the process id of the Scrapy process):
```
kill -QUIT <pid>
```

Debugger extension

class scrapy.extensions.periodic_log.Debugger

Invokes a Python debugger inside a running Scrapy process when a SIGUSR2 signal is received. After the debugger is exited, the Scrapy process continues running normally.

This extension only works on POSIX-compliant platforms (i.e. not Windows).