Writing a lambda expression breaks down to understanding three steps: identifying the type of the lambda expression you want to write finding the right method to implement implementing this method. This is really all there is to it. Let us see these three steps in detail. Identifying the Type of a Lambda Expression

Lambda Expressions¶ Small anonymous functions can be created with the lambda keyword. This function returns the sum of its two arguments: lambda a, b: a+b. Lambda functions can be used wherever function objects are required. They are syntactically restricted to a single expression.

The lambda functions do not need a return statement, they always return a single expression. What is callback in Lambda function? The third argument, callback , is a function that you can call in non-async handlers to send a response. The callback function takes two arguments: an Error and a response.