watchme

The URL watcher will watch for changes in web content. To set up a task of this type, you need to minimally provide a url to watch for changes. Given that we have created a watcher called “watcher”:

$ watchme create watcher

Add a Task

You would then want to add a task to it. The general format to add a task looks like this:

$ watchme add-task <watcher> task-<name> key1@value1 key2@value2

The key and value pairs are going to vary based on the watcher, however since a URL task is going to watch for changes at a url (at a frequency determined by the watcher schedule), it follows that adding the task minimally requires a url parameter.

Task Parameters

A urls task has the following parameters shared across functions.

Name Required Default Example Notes
url Yes undefined url@https://www.reddit.com/r/hpc validated starts with http
func No get_task func@download_task must be defined in tasks.py
regex No undefined regex@[0-9]+ if text, filter to regular expression

Task Headers

For some tasks, you can add one or more headers to the request by specifying header_<name>. For example, to add the header “Token” I could do header_Token=123456. By default, each task has the User-Agent header added, as it typically helps. If you want to disable this, add the header_User-Agent to be empty, or change it to something else.

Lists of URL Parameters

For the “Get” and “Get with selection” tasks, you might want to include url parameters. For example, you might want to loop through a set of pages, meaning ending the url with ?page=1 through ?page=9. You can do that with the url_param_<name> prefix. As an example, here is how we would do that. The following task loops through 7 pages of Pusheen dolls, and collects the text value (get_text@true) from the result of selection page elements by the .money class.

$ watchme add-task pusheen task-pusheencom url@https://shop.pusheen.com/collections/pusheen func@get_url_selection get_text@true selection@.money url_param_page@1,2,3,4,5,6,7

Specifically, note how we specified the “page” parameter for the url, with commas separated each call separately.

url_param_page@1,2,3,4,5,6,7

If you wanted to add another parameter (for each page) you can think of the commas as indexing. So you might do this:

url_param_name@V,V,V,V,V,V,V

or to skip the third page call (page=3) for the name parameter, just leave it empty:

url_param_name@V,V,,V,V,V,V

Tasks Available

For all tasks above, the Watcher runs them using multiprocessing so you can assume efficiency.

1. Get a URL Task

This task will watch for changes at an entire URL, meaning tracking the entire page. For example, here is a page I wanted to watch for changes:

$ watchme add-task watcher task-get url@https://httpbin.org/get
[task-get]
url  = https://httpbin.org/get
active  = true
type  = urls

In the above, we added the task “task-get” to the watcher called “watcher” and we defined the parameter “url” to be https://httpbin.org/get. As a confirmation that the task was added, the configuration is printed to the screen. This task is appropriate for content that you want returned as a string, and then saved to a text file to the repository. By default, it will be saved as result.txt. If you want to customize the extension (e.g., get a json object and save as result.json) specify the save_as parameter:

$ watchme add-task watcher task-get url@https://httpbin.org/get save_as@json

If you anticipate a list of results and want to save to separate jsons (one per entry) then specify save_as@jsons

$ watchme add-task watcher task-get url@https://httpbin.org/get save_as@jsons

Thus, the following custom parameters can be added:

Name Required Default Example Notes
save_as No unset save_as@json default saves to text, or can be specified as json/jsons.
file_name No unset file_name@image.png the filename to save, only for download_task
url_param_ No unset url_param_name@V,V,V,V,V,V,V use commas to separate separate url calls
header_* No unset header_Accept@json Define 1 or headers

If you specify “save_as” to be json, you will get a results.json unless you specify another file name.

2. Post to a URL Task

This task will post to get changes from a URL, ideal for watching restful API endpoints. For example, here is a page I wanted to watch for changes:

$ watchme add-task watcher task-api-post url@https://httpbin.org/post file_name@post-latest.json func@post_task

[task-api-post]
url  = https://httpbin.org/post
file_name  = post-latest.json
func  = post_task
active  = true
type  = urls

Since we are using the task “post_task” it defaults to saving json, so I don’t need to set “save_as” (unless you want to save to a different type). Notice that I’ve specified a custom file_name too.

In the above, we added the task “task-api-post” to the watcher called “watcher” and we defined the parameter “url” to be the endpoint that we want to post to. The following custom parameters can be added:

Name Required Default Example Notes
save_as No unset save_as@json default saves to text, or can be specified as json.
file_name No unset file_name@image.png the filename to save, only for download_task
json_param_* No unset json_param_page@1 Define 1 or more parameters (json/data) for the post
header_* No unset header_Accept@json Define 1 or headers

You can define parameters for the POST with one or more definitions of json_param_<name>, where the name corresponds with the variable name you want (the json_param_ portion is removed). If you want to do multiple POSTS with different sets of parameters, you can separate them by commas. The same is True for headers, except you can only define one set shared across POSTS. Use header_<name> to define one or more.

3. Download Content

You might also want to download some content or object, and save it to file to track changes over time. You can do this by using the urls type watcher and specifying the variable func to be “download_task”:

$ watchme add-task watcher task-download url@https://httpbin.org/image/png func@download_task file_name@image.png
[task-download]
url  = https://httpbin.org/image/png
func  = download_task
file_name = image.png
active  = true
type  = urls
Name Required Default Example Notes
no_verify_ssl No unset no_verify_ssl@true  
write_format No unset write_format@wb only for download_task
file_name No unset file_name@image.png the filename to save, only for download_task
header_* No unset header_Accept@json Define 1 or headers

4. Select on a Page Task

You might be interested in scraping one div (or general selection, such as a section identified by a class or id) on a page. For this purpose, you can use the function get_url_selection. Note that you will need to install an extra set of dynamic packages to do this:

$ pip install watchme[watcher-urls-dynamic]

This task will watch for changes based on a selection from a page. For example, let’s say there is a text value on a page with an air quality value. We would want to define this as the selection:

$ watchme create air-quality
$ watchme add-task air-quality task-air-oakland url@http://aqicn.org/city/california/alameda/oakland-west func@get_url_selection selection@#aqiwgtvalue file_name@oakland.txt get_text@true
[task-air-oakland]
url  = http://aqicn.org/city/california/alameda/oakland-west
func  = get_url_selection
selection  = #aqiwgtvalue
file_name  = oakland.txt
get_text  = true
active  = true
type  = urls

We set “get_text” to true (or anything) so that we are sure to grab the text content of our selection. The following parameters apply for this function:

Name Required Default Example Notes  
selection Yes unset #idname    
get_text No unset get_text@true if found, return text from the selection  
attributes No unset style,id or id for some selection, return attributes  
file_name No unset file_name@image.png the filename to save, only for download_task  
url_param_ No unset url_param_name@V,V,V,V,V,V,V use commas to separate separate url calls  
header_* No unset header_Accept@json Define 1 or headers  

We can run the task:

$ watchme activate air-quality
$ watchme run air-quality

and then see the result!

$ tree $HOME/.watchme/air-quality
├── task-air-oakland
│   ├── oakland.txt
│   └── TIMESTAMP
└── watchme.cfg

The file itself has the value of 30, the air quality in Oakland today. I would next want to schedule this at some frequency to collect data consistently when my computer is on.

$ watchme schedule air-quality @hourly

Verify the Addition

We can also confirm this section has been written to file, either by looking at a watcher directly:

$ cat /home/vanessa/.watchme/watcher/watchme.cfg 
[watcher]
active = false

[task-get]
url  = https://httpbin.org/get
active  = true
type  = urls

or using inspect:

$ watchme inspect air-quality

You don’t actually need to use watchme to write these files - you can write the sections in a text editor if you are comfortable with the format. The sections are always validated when the watcher is run.

Force Addition

If for some reason you want to overwrite a task, you need to use force. Here is what it looks like when you don’t, and the task already exists:

$ watchme add watcher task-reddit-hpc url@https://www.reddit.com/r/hpc
ERROR task-reddit-hpc exists, use --force to overwrite.

Active Status

If you want to change the default active status, use --active false. By default, tasks added to watchers are active. Here is what the same command above would have looked like setting active to false:

$ watchme add watcher task-reddit-hpc url@https://www.reddit.com/r/hpc --active false
[task-reddit-hpc]
url  = https://www.reddit.com/r/hpc
active  = false
type  = urls