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Handler



The Lambda function handler is the method in your function code that processes events. When your function is invoked, Lambda runs the handler method. When the handler exits or returns a response, it becomes available to handle another event.




handler



A function handler can be any name; however, the default name in the Lambda console is lambda_function.lambda_handler. This function handler name reflects the function name (lambda_handler) and the file where the handler code is stored (lambda_function.py).


The following example shows a function called lambda_handler that uses the python3.8 Lambda runtime. The function accepts user input of a first and last name, and returns a message that contains data from the event it received as input.


The following example shows a function called lambda_handler that uses the python3.8 Lambda runtime. The function uses event data passed by Lambda at runtime. It parses the environment variable in AWS_REGION returned in the JSON response.


The following example Lambda Python function code on GitHub shows a function called lambda_handler that uses the python3.6 Lambda runtime. The function accepts user input and returns a calculation to the user.


The handler interface does not have to provide a consistent look of the data (for example, dirty reads are permitted), so the storage engine can use optimizations that SELECT does not normally permit.


An empty handler will create a proxy that behaves, in almost all respects, exactly like the target. By defining any of a set group of functions on the handler object, you can customize specific aspects of the proxy's behavior. For example, by defining get() you can provide a customized version of the target's property accessor.


\n An empty handler will create a proxy that behaves, in almost all respects, exactly like\n the target. By defining any of a set group of functions on the handler\n object, you can customize specific aspects of the proxy's behavior. For example, by\n defining get() you can provide a customized version of the target's\n property accessor.\n


A "handler" is an internal Apache representation of the action to be performed when a file is called. Generally, files have implicit handlers, based on the file type. Normally, all files are simply served by the server, but certain file types are "handled" separately.


Handlers may also be configured explicitly, based on either filename extensions or on location, without relation to file type. This is advantageous both because it is a more elegant solution, and because it also allows for both a type and a handler to be associated with a file. (See also Files with Multiple Extensions.)


The following directives will enable the send-as-is handler, which is used for files which contain their own HTTP headers. All files in the /web/htdocs/asis/ directory will be processed by the send-as-is handler, regardless of their filename extensions.


If you wish to have your module engage a handler, you need only to set r->handler to the name of the handler at any time prior to the invoke_handler stage of the request. Handlers are implemented as they were before, albeit using the handler name instead of a content type. While it is not necessary, the naming convention for handlers is to use a dash-separated word, with no slashes, so as to not invade the media type name-space.


A handler function accepts a Psr\Http\Message\RequestInterface and array ofrequest options and returns a GuzzleHttp\Promise\PromiseInterface that isfulfilled with a Psr\Http\Message\ResponseInterface or rejected with anexception.


You can provide a custom handler to a client using the handler option ofa client constructor. It is important to understand that several requestoptions used by Guzzle require that specific middlewares wrap the handler usedby the client. You can ensure that the handler you provide to a client uses thedefault middlewares by wrapping the handler in theGuzzleHttp\HandlerStack::create(callable $handler = null) static method.


Middleware functions return a function that accepts the next handler to invoke.This returned function then returns another function that acts as a composedhandler-- it accepts a request and options, and returns a promise that isfulfilled with a response. Your composed middleware can modify the request,add custom request options, and modify the promise returned by the downstreamhandler.


A handler stack represents a stack of middleware to apply to a base handlerfunction. You can push middleware to the stack to add to the top of the stack,and unshift middleware onto the stack to add to the bottom of the stack. Whenthe stack is resolved, the handler is pushed onto the stack. Each value isthen popped off of the stack, wrapping the previous value popped off of thestack.


As stated earlier, a handler is a function accepts aPsr\Http\Message\RequestInterface and array of request options and returnsa GuzzleHttp\Promise\PromiseInterface that is fulfilled with aPsr\Http\Message\ResponseInterface or rejected with an exception.


When script developers want to factor and re-use their code, they can turn to handlers. A handler is a collection of statements that can be invoked by name. Handlers are also known as functions, subroutines, or methods.


A handler is a collection of statements that can be invoked by name. Handlers are useful in scripts that perform the same action in more than one place. You can package statements that perform a specific task as a handler, give it a descriptive name, and call it from anywhere in the script. This makes the script shorter and easier to maintain.


When you call a handler, you must list its parameters according to how they are specified in its definition. Handlers may have labeled, positional, or interleaved parameters, described in subsequent sections. If a parameter has a specified class, AppleScript will coerce the actual value to that class as if using the as operator. If a parameter has a default value, that parameter may be omitted.


The following is a definition for a simple handler that takes any parameter value that can be displayed as text (presumably one representing a date) and displays it in a dialog box. The handler name is rock; its parameter is around the clock, where around is a parameter label and clock is the parameter name (the is an AppleScript filler for readability):


A handler can have no parameters. To indicate that a handler has no parameters, you include a pair of empty parentheses after the handler name in both the handler definition and the handler call. For example, the following helloWorld script has no parameters.


To define a handler with labeled parameters, you list the labels to use when calling the handler and the statements to be executed when it is called. (The syntax is shown in Handler Syntax (Labeled Parameters).)


Handlers with labeled parameters can also have a direct parameter. With the exception of the direct parameter, which must directly follow the handler name, labeled parameters can appear in any order, with the labels from the handler definition identifying the parameter values. This includes parameters listed in given, with, and without clauses (of which there can be any number).


The first line of the minimumValue handler specifies the parameters of the handler. To call a handler with positional parameters you list the parameters in the same order as they are specified in the handler definition.


If a handler call is part of an expression, AppleScript uses the value returned by the handler to evaluate the expression. For example, to evaluate the following expression, AppleScript first calls minimumValue, then evaluates the rest of the expression.


You can create a handler whose positional parameters define a pattern to match when calling the handler. For example, the following handler takes a single parameter whose pattern consists of two items in a list:


A parameter pattern can be much more complex than a single list. The handler in the next example takes two numbers and a record whose properties include a list of bounds. The handler displays a dialog box summarizing some of the passed information.


A handler with interleaved parameters is a special case of one with positional parameters. The definition shows the order in which to list parameters when calling the handler and the statements to be executed when the handler is called, but the name of the handler is broken into pieces and interleaved with the parameters, which can make it easier to read. Handlers with interleaved parameters may be used in any script, but are especially useful with bridged Objective-C methods, since they naturally resemble Objective-C syntax. The syntax is shown in Handler Syntax (Interleaved Parameters).


To call a handler with interleaved parameters, list the parameters in the same order as they are specified in the handler definition. Despite the resemblance to labeled parameters, the parameters may not be reordered. Also, the call must be explicitly sent to an object, even if the target object is the default, it. For example:


Note: The actual name of an interleaved-parameter handler is all the name parts strung together with underscores, and is equivalent to a handler defined using that name with positional parameters. For example, these two handler declarations are equivalent:


The effect is as if the handler began with set x to x as integer; if coercing the actual value to an integer fails, AppleScript throws an appropriate error, which may be caught with a try block. The class may be a list of classes, as described in Operators Reference.


Labeled parameters may be declared with a default value by following the formal parameter name with :literal. Doing so makes the parameter optional when called. For example, this declares a make handler with a default value for the with data parameter:


This handler can now be called without supplying a with data parameter; the handler would see theData set to the specified default missing value, which it could then test for and handle appropriately. 041b061a72


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