your code in the same way you would if it were synchronous. This is especially important for error handling, since try/except blocks work as you would expect in coroutines while this is difficult to achieve RequestHandler for all your specific handlers. Handling request input The request handler can access the object representing the current request with self.request. See the class definition for HTTPServerRequest HTTPServerRequest for a complete list of attributes. Request data in the formats used by HTML forms will be parsed for you and is made available in methods like get_query_argument and get_body_argument. class

main coroutine The Application object Subclassing RequestHandler Handling request input Overriding RequestHandler methods Error Handling Redirection Asynchronous handlers Templates and UI Configuring and security Cookies and signed cookies User authentication Third party authentication Cross-site request forgery protection DNS Rebinding Running and deploying Processes and ports Running behind a load your code in the same way you would if it were synchronous. This is especially important for error handling, since try/except blocks work as you would expect in coroutines while this is difficult to achieve

Evaluation: Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 10.5 Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 10.6 Tasks (aka Coroutines) C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385 29 Handling Operating System Variation 388CONTENTS vi 30 Environment Variables 389 30.1 File locations . Extracting useful information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 34.3 Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439 34.4 Exception stacks

Evaluation: Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 10.5 Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 10.6 Tasks (aka Coroutines) C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385 29 Handling Operating System Variation 388CONTENTS vi 30 Environment Variables 389 30.1 File locations . Extracting useful information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 34.3 Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439 34.4 Exception stacks

Evaluation: Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 10.5 Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 10.6 Tasks (aka Coroutines) C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 385 29 Handling Operating System Variation 388CONTENTS vi 30 Environment Variables 389 30.1 File locations . Extracting useful information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 438 34.3 Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 439 34.4 Exception stacks

Evaluation: Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 9.5 Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 9.6 Tasks (aka Coroutines) C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 28 Handling Operating System Variation 366 29 Environment Variables 367 29.1 File locations . . . . . . . Extracting useful information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 33.3 Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412 33.4 Exception stacks

Evaluation: Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 9.5 Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 9.6 Tasks (aka Coroutines) C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 363 28 Handling Operating System Variation 366 29 Environment Variables 367 29.1 File locations . . . . . . . Extracting useful information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 411 33.3 Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 412 33.4 Exception stacks

Evaluation: Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 10.5 Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 10.6 Tasks (aka Coroutines) C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388 29 Handling Operating System Variation 391CONTENTS vi 30 Environment Variables 392 30.1 File locations . Extracting useful information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448 34.3 Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 34.4 Exception stacks

Evaluation: Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 10.5 Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 10.6 Tasks (aka Coroutines) C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388 29 Handling Operating System Variation 391CONTENTS vi 30 Environment Variables 392 30.1 File locations . Extracting useful information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448 34.3 Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 34.4 Exception stacks

Evaluation: Loops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 10.5 Exception Handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104 10.6 Tasks (aka Coroutines) C++ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 388 29 Handling Operating System Variation 391CONTENTS vi 30 Environment Variables 392 30.1 File locations . Extracting useful information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 448 34.3 Error handling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 449 34.4 Exception stacks