This can be used for all kinds of useful things, made possible because functions are objects and just necessary just instructions. Stack Overflow for Teams — Start collaborating and sharing organizational knowledge.

Create a free Team Why Teams? Learn more about Collectives. Learn more about Teams. What does the "at" symbol do in Python? Ask Question. Asked 11 years, 6 months ago.

Modified 7 months ago. Viewed k times. What does the symbol do in Python? python syntax python-decorators. Improve this question. edited Apr 19 at Mateen Ulhaq asked Jun 17, at AJ AJ Add a comment.

Sorted by: Reset to default. Highest score default Trending recent votes count more Date modified newest first Date created oldest first.

An symbol at the beginning of a line is used for class and function decorators : PEP Decorators Python Decorators The most common Python decorators are: property classmethod staticmethod An in the middle of a line is probably matrix multiplication: as a binary operator.

Improve this answer. answered Jun 17, at FogleBird FogleBird It looks like it can also be a matrix multiplication operator as well: stackoverflow. edited Jan 2, at answered Apr 5, at Morgan Wilde Morgan Wilde In the case Flasks's app. What's the syntactic or practical benefit of having decorators here, instead of for example just calling something like app. The latter example is common with Node. js http. Server and Express routes. This is a simple implementation of matrix multiplication.

edited May 20, at Peter Mortensen answered Mar 11, at jinhwanlazy jinhwanlazy 3, 1 1 gold badge 10 10 silver badges 9 9 bronze badges. Are there any other overridable operators like this? Are there any others lurking out there? ThomasKimber Sure. Check out everything under docs. answered Feb 10, at Matheus Araujo Matheus Araujo 5, 2 2 gold badges 21 21 silver badges 23 23 bronze badges.

In short, it is used in decorator syntax and for matrix multiplication. How could you discover this on your own? But the word, "decorator" is a link to the glossary , which tells us: decorator A function returning another function, usually applied as a function transformation using the wrapper syntax.

The decorator syntax is merely syntactic sugar, the following two function definitions are semantically equivalent: def f That about sums up the usage for in the context of decorators. T, dot inv dot dot H, V , H. edited Jun 2, at MattDMo answered Sep 3, at answered May 26, at AbstProcDo AbstProcDo 19k 15 15 gold badges 75 75 silver badges bronze badges.

This is the absolute best page in this whole page, you explains things so well, ONLY after reading your answer I was able to understand it!! answered Nov 7, at Decorators can be used in multiple different ways as shown below: As a function There are many ways to write custom decorators, but the simplest way is to write a function that returns a subfunction that wraps the original function call.

def foo print "foo" def bar print "bar" Properties The properties provide a built-in descriptor type that knows how to link an attribute to a set of methods. x1, self. x2, self. x2 - self. y2 - self. format self. y1, self. y2 The best syntax for creating properties is using property as a decorator.

x1 width. setter def width self, value : self. y1 height. setter def height self, value : self. answered Jul 1, at iun1x iun1x 10 10 silver badges 12 12 bronze badges. answered Mar 7, at dpodbori dpodbori 2 2 silver badges 7 7 bronze badges. can be a math operator or a DECORATOR but what you mean is a decorator. This code: def func f : return f func lambda :"HelloWorld" using decorators can be written like: def func f : return f func def name : return "Hello World" name Decorators can have arguments.

edited Dec 2, at The Amateur Coder 3 3 gold badges 11 11 silver badges 31 31 bronze badges. user user Peter Rowell Peter Rowell Python decorator is like a wrapper of a function or a class. answered Jan 9, at Mohammed Jubayer Mohammed Jubayer 1, 1 1 gold badge 11 11 silver badges 5 5 bronze badges.

To say what others have in a different way: yes, it is a decorator. In Python, it's like: Creating a function follows under the call Calling another function to operate on your created function. This returns a new function. The function that you call is the argument of the. Replacing the function defined with the new function returned. answered Feb 7, at Mayur Patel Mayur Patel 1 1 gold badge 7 7 silver badges 15 15 bronze badges.

answered Nov 15, at Aswin Aswin 4 4 silver badges 12 12 bronze badges. While true, there are much simpler or at least more elegant ways to do this, at least in pandas. Following your example, you could just do df[df. In general, the goal of the project is to emulate enough of a subset of a web browser to be useful for testing and scraping real-world web applications. The latest versions of jsdom require Node.

js v14 or newer. Versions of jsdom below v20 still work with previous Node. js versions, but are unsupported. To use jsdom, you will primarily use the JSDOM constructor, which is a named export of the jsdom main module. Pass the constructor a string. You will get back a JSDOM object, which has a number of useful properties, notably window :.

The resulting object is an instance of the JSDOM class, which contains a number of useful properties and methods besides window. In general, it can be used to act on the jsdom from the "outside," doing things that are not possible with the normal DOM APIs.

For simple cases, where you don't need any of this functionality, we recommend a coding pattern like. Full documentation on everything you can do with the JSDOM class is below, in the section " JSDOM Object API".

The JSDOM constructor accepts a second parameter which can be used to customize your jsdom in the following ways. Note that both url and referrer are canonicalized before they're used, so e. if you pass in "https:example. If you pass an unparseable URL, the call will throw.

URLs are parsed and serialized according to the URL Standard. jsdom's most powerful ability is that it can execute scripts inside the jsdom. These scripts can modify the content of the page and access all the web platform APIs jsdom implements. However, this is also highly dangerous when dealing with untrusted content. js environment, and thus to your machine. As such, the ability to execute scripts embedded in the HTML is disabled by default:.

To enable executing scripts inside the page, you can use the runScripts: "dangerously" option:. Again we emphasize to only use this when feeding jsdom code you know is safe. If you use it on arbitrary user-supplied code, or code from the Internet, you are effectively running untrusted Node.

js code, and your machine could be compromised. To do this, add the option resources: "usable" as described below. You'll likely also want to set the url option, for the reasons discussed there. However, event handler properties , like div. This includes things like window. Array , window. Promise , etc. It also, notably, includes window. eval , which allows running scripts, but with the jsdom window as the global:. Note that in the default configuration, without setting runScripts , the values of window.

eval , etc. will be the same as those provided by the outer Node. js environment. That is, window. eval will not run scripts in a useful way. We strongly advise against trying to "execute scripts" by mashing together the jsdom and Node global environments e. by doing global.

window , and then executing scripts or test code inside the Node global environment. Instead, you should treat jsdom like you would a browser, and run all scripts and tests that need access to a DOM inside the jsdom environment, using window. eval or runScripts: "dangerously". Finally, for advanced use cases you can use the dom. getInternalVMContext method, documented below. jsdom does not have the capability to render visual content, and will act like a headless browser by default.

It provides hints to web pages through APIs such as document. hidden that their content is not visible. When the pretendToBeVisual option is set to true , jsdom will pretend that it is rendering and displaying content.

It does this by:. Note that jsdom still does not do any layout or rendering , so this is really just about pretending to be visual, not about implementing the parts of the platform a real, visual web browser would implement. By default, jsdom will not load any subresources such as scripts, stylesheets, images, or iframes. If you'd like jsdom to load such resources, you can pass the resources: "usable" option, which will load all usable resources.

Those are:. When attempting to load resources, recall that the default value for the url option is "about:blank" , which means that any resources included via relative URLs will fail to load. So, you'll likely want to set a non-default value for the url option in those cases, or use one of the convenience APIs that do so automatically.

This resource loader system is new as of jsdom v Please file an issue to discuss! To more fully customize jsdom's resource-loading behavior, you can pass an instance of the ResourceLoader class as the resources option value:. You can further customize resource fetching by subclassing ResourceLoader and overriding the fetch method. For example, here is a version that only returns results for requests to a trusted origin:.

jsdom will call your custom resource loader's fetch method whenever it encounters a "usable" resource, per the above section. The method takes a URL string, as well as a few options which you should pass through unmodified if calling super. It must return a promise for a Node. js Buffer object, or return null if the resource is intentionally not to be loaded. In general, most cases will want to delegate to super.

fetch , as shown. One of the options you will receive in fetch will be the element if applicable that is fetching a resource.

Like web browsers, jsdom has the concept of a "console". This records both information directly sent from the page, via scripts executing inside the document, as well as information from the jsdom implementation itself.

We call the user-controllable console a "virtual console", to distinguish it from the Node. js console API and from the inside-the-page window. console API. By default, the JSDOM constructor will return an instance with a virtual console that forwards all its output to the Node. js console. To create your own virtual console and pass it to jsdom, you can override this default by doing.

Code like this will create a virtual console with no behavior. You can give it behavior by adding event listeners for all the possible console methods:. Note that it is probably best to set up these event listeners before calling new JSDOM , since errors or console-invoking script might occur during parsing. If you simply want to redirect the virtual console output to another console, like the default Node. js one, you can do.

There is also a special event, "jsdomError" , which will fire with error objects to report errors from jsdom itself. This is similar to how error messages often show up in web browser consoles, even if they are not initiated by console. So far, the following errors are output this way:. If you're using sendTo c to send errors to c , by default it will call c. error errorStack[, errorDetail] with information from "jsdomError" events.

If you'd prefer to maintain a strict one-to-one mapping of events to method calls, and perhaps handle "jsdomError" s yourself, then you can do. Like web browsers, jsdom has the concept of a cookie jar, storing HTTP cookies. Cookies that have a URL on the same domain as the document, and are not marked HTTP-only, are accessible via the document.

cookie API. Additionally, all cookies in the cookie jar will impact the fetching of subresources. By default, the JSDOM constructor will return an instance with an empty cookie jar. To create your own cookie jar and pass it to jsdom, you can override this default by doing. This is mostly useful if you want to share the same cookie jar among multiple jsdoms, or prime the cookie jar with certain values ahead of time.

Cookie jars are provided by the tough-cookie package. The jsdom. CookieJar constructor is a subclass of the tough-cookie cookie jar which by default sets the looseMode: true option, since that matches better how browsers behave.

If you want to use tough-cookie's utilities and classes yourself, you can use the jsdom. toughCookie module export to get access to the tough-cookie module instance packaged with jsdom.

jsdom allows you to intervene in the creation of a jsdom very early: after the Window and Document objects are created, but before any HTML is parsed to populate the document with nodes:. This is especially useful if you are wanting to modify the environment in some way, for example adding shims for web platform APIs jsdom does not support. Once you have constructed a JSDOM object, it will have the following useful capabilities:.

The property window retrieves the Window object that was created for you. The properties virtualConsole and cookieJar reflect the options you pass in, or the defaults created for you if nothing was passed in for those options.

The serialize method will return the HTML serialization of the document, including the doctype:. The nodeLocation method will find where a DOM node is within the source document, returning the parse5 location info for the node:.

Note that this feature only works if you have set the includeNodeLocations option; node locations are off by default for performance reasons. The built-in vm module of Node. js is what underpins jsdom's script-running magic. Some advanced use cases, like pre-compiling a script and then running it multiple times, benefit from using the vm module directly with a jsdom-created Window.

To get access to the contextified global object , suitable for use with the vm APIs, you can use the getInternalVMContext method:. This is somewhat-advanced functionality, and we advise sticking to normal DOM APIs such as window. eval or document. createElement "script" unless you have very specific needs. Note that this method will throw an exception if the JSDOM instance was created without runScripts set, or if you are using jsdom in a web browser.

The top property on window is marked [Unforgeable] in the spec, meaning it is a non-configurable own property and thus cannot be overridden or shadowed by normal code running inside the jsdom, even using Object. Similarly, at present jsdom does not handle navigation such as setting window.

However, if you're acting from outside the window, e. in some test framework that creates jsdoms, you can override one or both of these using the special reconfigure method:. Note that changing the jsdom's URL will impact all APIs that return the current document URL, such as window. location , document. URL , and document.

documentURI , as well as the resolution of relative URLs within the document, and the same-origin checks and referrer used while fetching subresources. It will not, however, perform navigation to the contents of that URL; the contents of the DOM will remain unchanged, and no new instances of Window , Document , etc. will be created. In addition to the JSDOM constructor itself, jsdom provides a promise-returning factory method for constructing a jsdom from a URL:.

The returned promise will fulfill with a JSDOM instance if the URL is valid and the request is successful. Any redirects will be followed to their ultimate destination.

The options provided to fromURL are similar to those provided to the JSDOM constructor, with the following additional restrictions and consequences:.

Similar to fromURL , jsdom also provides a fromFile factory method for constructing a jsdom from a filename:. The returned promise will fulfill with a JSDOM instance if the given file can be opened.

As usual in Node. js APIs, the filename is given relative to the current working directory. The options provided to fromFile are similar to those provided to the JSDOM constructor, with the following additional defaults:.

For the very simplest of cases, you might not need a whole JSDOM instance with all its associated power. You might not even need a Window or Document! Instead, you just need to parse some HTML, and get a DOM object you can manipulate. For that, we have fragment , which creates a DocumentFragment from a given string:.

Here frag is a DocumentFragment instance, whose contents are created by parsing the provided string. It's also important to note that the resulting DocumentFragment will not have an associated browsing context : that is, elements' ownerDocument will have a null defaultView property, resources will not load, etc.

All invocations of the fragment factory result in DocumentFragment s that share the same template owner Document. This allows many calls to fragment with no extra overhead. But it also means that calls to fragment cannot be customized with any options. Note that serialization is not as easy with DocumentFragment s as it is with full JSDOM objects. If you need to serialize your DOM, you should probably use the JSDOM constructor more directly.

But for the special case of a fragment containing a single element, it's pretty easy to do through normal means:.

To make this work, you need to include canvas as a dependency in your project, as a peer of jsdom. Since jsdom v13, version 2. x of canvas is required; version 1.

x is no longer supported. In addition to supplying a string, the JSDOM constructor can also be supplied binary data, in the form of a Node. js Buffer or a standard JavaScript binary data type like ArrayBuffer , Uint8Array , DataView , etc.

If the supplied contentType option contains a charset parameter, that encoding will override the sniffed encoding—unless a UTF-8 or UTF BOM is present, in which case those take precedence.

A JavaScript implementation of various web standards, for use with Node. Work fast with our official CLI. Learn more. Please sign in to use Codespaces. If nothing happens, download GitHub Desktop and try again. If nothing happens, download Xcode and try again.

There was a problem preparing your codespace, please try again. jsdom is a pure-JavaScript implementation of many web standards, notably the WHATWG DOM and HTML Standards, for use with Node. In general, the goal of the project is to emulate enough of a subset of a web browser to be useful for testing and scraping real-world web applications. The latest versions of jsdom require Node. js v14 or newer. Versions of jsdom below v20 still work with previous Node.

js versions, but are unsupported. To use jsdom, you will primarily use the JSDOM constructor, which is a named export of the jsdom main module. Pass the constructor a string. You will get back a JSDOM object, which has a number of useful properties, notably window :. The resulting object is an instance of the JSDOM class, which contains a number of useful properties and methods besides window.

In general, it can be used to act on the jsdom from the "outside," doing things that are not possible with the normal DOM APIs. For simple cases, where you don't need any of this functionality, we recommend a coding pattern like. Full documentation on everything you can do with the JSDOM class is below, in the section " JSDOM Object API". The JSDOM constructor accepts a second parameter which can be used to customize your jsdom in the following ways.

Note that both url and referrer are canonicalized before they're used, so e. if you pass in "https:example. If you pass an unparseable URL, the call will throw. URLs are parsed and serialized according to the URL Standard. jsdom's most powerful ability is that it can execute scripts inside the jsdom. These scripts can modify the content of the page and access all the web platform APIs jsdom implements. However, this is also highly dangerous when dealing with untrusted content.

js environment, and thus to your machine. As such, the ability to execute scripts embedded in the HTML is disabled by default:. To enable executing scripts inside the page, you can use the runScripts: "dangerously" option:. Again we emphasize to only use this when feeding jsdom code you know is safe. If you use it on arbitrary user-supplied code, or code from the Internet, you are effectively running untrusted Node.

js code, and your machine could be compromised. To do this, add the option resources: "usable" as described below. You'll likely also want to set the url option, for the reasons discussed there. However, event handler properties , like div. This includes things like window.

Array , window. Promise , etc. It also, notably, includes window. eval , which allows running scripts, but with the jsdom window as the global:. Note that in the default configuration, without setting runScripts , the values of window. eval , etc. will be the same as those provided by the outer Node.

js environment. That is, window. eval will not run scripts in a useful way. We strongly advise against trying to "execute scripts" by mashing together the jsdom and Node global environments e. by doing global. window , and then executing scripts or test code inside the Node global environment. Instead, you should treat jsdom like you would a browser, and run all scripts and tests that need access to a DOM inside the jsdom environment, using window.

eval or runScripts: "dangerously". Finally, for advanced use cases you can use the dom. getInternalVMContext method, documented below. jsdom does not have the capability to render visual content, and will act like a headless browser by default.

It provides hints to web pages through APIs such as document. hidden that their content is not visible. When the pretendToBeVisual option is set to true , jsdom will pretend that it is rendering and displaying content. It does this by:. Note that jsdom still does not do any layout or rendering , so this is really just about pretending to be visual, not about implementing the parts of the platform a real, visual web browser would implement.

By default, jsdom will not load any subresources such as scripts, stylesheets, images, or iframes. If you'd like jsdom to load such resources, you can pass the resources: "usable" option, which will load all usable resources. Those are:. When attempting to load resources, recall that the default value for the url option is "about:blank" , which means that any resources included via relative URLs will fail to load.

So, you'll likely want to set a non-default value for the url option in those cases, or use one of the convenience APIs that do so automatically. This resource loader system is new as of jsdom v Please file an issue to discuss! To more fully customize jsdom's resource-loading behavior, you can pass an instance of the ResourceLoader class as the resources option value:. You can further customize resource fetching by subclassing ResourceLoader and overriding the fetch method. For example, here is a version that only returns results for requests to a trusted origin:.

jsdom will call your custom resource loader's fetch method whenever it encounters a "usable" resource, per the above section. The method takes a URL string, as well as a few options which you should pass through unmodified if calling super. It must return a promise for a Node. js Buffer object, or return null if the resource is intentionally not to be loaded.

In general, most cases will want to delegate to super. fetch , as shown. One of the options you will receive in fetch will be the element if applicable that is fetching a resource.

Like web browsers, jsdom has the concept of a "console". This records both information directly sent from the page, via scripts executing inside the document, as well as information from the jsdom implementation itself. We call the user-controllable console a "virtual console", to distinguish it from the Node.

js console API and from the inside-the-page window. console API. By default, the JSDOM constructor will return an instance with a virtual console that forwards all its output to the Node.

js console. To create your own virtual console and pass it to jsdom, you can override this default by doing. Code like this will create a virtual console with no behavior. You can give it behavior by adding event listeners for all the possible console methods:. Note that it is probably best to set up these event listeners before calling new JSDOM , since errors or console-invoking script might occur during parsing.

If you simply want to redirect the virtual console output to another console, like the default Node. js one, you can do. There is also a special event, "jsdomError" , which will fire with error objects to report errors from jsdom itself. This is similar to how error messages often show up in web browser consoles, even if they are not initiated by console. So far, the following errors are output this way:. If you're using sendTo c to send errors to c , by default it will call c.

error errorStack[, errorDetail] with information from "jsdomError" events. If you'd prefer to maintain a strict one-to-one mapping of events to method calls, and perhaps handle "jsdomError" s yourself, then you can do. Like web browsers, jsdom has the concept of a cookie jar, storing HTTP cookies.

Cookies that have a URL on the same domain as the document, and are not marked HTTP-only, are accessible via the document.

If format is one of the native format specifiers from the struct module, indexing with an integer or a tuple of integers is also supported and returns a single element with the correct type. If iterable is already a tuple, it is returned unchanged. Touch ID. The same concept exists for classes, but is less commonly used there. We call the user-controllable console a "virtual console", to distinguish it from the Node. Unlike split when a delimiter string sep is given, this method returns an empty list for the empty string, and a terminal line break does not result in an extra line:.

Categories:

• Binary Options
• Forex
• Forex Brokers
• Forex Bitcoin
• Binary Options online