rapidsms.contrib.handlers

The handlers contrib application provides three classes- BaseHandler, KeywordHandler, and PatternHandler- which can be extended to help you create RapidSMS applications quickly.

Installation

To define and use handlers for your RapidSMS project, you will need to add "rapidsms.contrib.handlers" to INSTALLED_APPS in your settings file:

INSTALLED_APPS = [
    ...
    "rapidsms.contrib.handlers",
    ...
]

Then you’ll also need to set RAPIDSMS_HANDLERS. The application will load the handler classes listed in RAPIDSMS_HANDLERS, as described in Handler Discovery.

RAPIDSMS_HANDLERS = [
    "rapidsms.contrib.handlers.KeywordHandler",
    "rapidsms.contrib.handlers.PatternHandler",
]

Usage

KeywordHandler

Many RapidSMS applications operate based on whether a message begins with a specific keyword. By subclassing KeywordHandler, you can easily create a simple, keyword-based application:

from rapidsms.contrib.handlers import KeywordHandler

class LightHandler(KeywordHandler):
    keyword = "light"

    def help(self):
        self.respond("Send LIGHT ON or LIGHT OFF.")

    def handle(self, text):
        if text.upper() == "ON":
            self.respond("The light is now turned on.")

        elif text.upper() == "OFF":
            self.respond("Thanks for turning off the light!")

        else:
            self.help()

Your handler must define three things: keyword, help(), and handle(text). When a message is received that begins with the keyword (case insensitive; leading whitespace is allowed), the remaining text is passed to the handle method of the class. If no additional non-whitespace text is included with the message, help is called instead. For example:

> light
< Send LIGHT ON or LIGHT OFF.
> light on
< The light is now turned on.
> light off
< Thanks for turning off the light!
> light something else
< Send LIGHT ON or LIGHT OFF.

The handler also treats ,, :, and ; after the keyword the same as whitespace. For example:

> light
< Send LIGHT ON or LIGHT OFF.
> light:on
< The light is now turned on.
> light, off
< Thanks for turning off the light!
> light :,; on
< The light is now turned on.

Tip

Technically speaking, the incoming message text is compared to a regular expression pattern.

The most common use case is to look for a single exact-match keyword. However, one could also match multiple keywords, for example keyword = "register|reg|join".

However, due to how we build the final regular expression, capturing matches using grouping in the keyword regular expression won’t work. If you need that, use the PatternHandler.

All non-matching messages are silently ignored to allow other applications and handlers to catch them.

For example implementations of KeywordHandler, see

Here’s documentation from the KeywordHandler class:

class rapidsms.contrib.handlers.KeywordHandler

This handler type can be subclassed to create simple keyword-based handlers. When a message is received, it is checked against the mandatory keyword attribute (a regular expression) for a prefix match. For example:

>>> class AbcHandler(KeywordHandler):
...    keyword = "abc"
...
...    def help(self):
...        self.respond("Here is some help.")
...
...    def handle(self, text):
...        self.respond("You said: %s." % text)

If the keyword is matched and followed by some text, the handle method is called:

>>> AbcHandler.test("abc waffles")
['You said: waffles.']

If just the keyword is matched, the help method is called:

>>> AbcHandler.test("abc")
['Here is some help.']

All other messages are silently ignored (as usual), to allow other apps or handlers to catch them.

handle(text)

Called when the keyword matches and text follows

Parameters:text – The text that follows the keyword. Any whitespace between the keyword and the text is not included.
help()

Called when the keyword matches but no text follows

keyword = None

A string specifying a regular expression matched against the beginning of the message. Not case sensitive.

PatternHandler

Note

Pattern-based handlers can work well for prototyping and simple use cases. For more complex parsing and message handling, we recommend writing a RapidSMS application with a custom handle phase.

The PatternHandler class can be subclassed to create applications which respond to a message when a specific pattern is matched:

from rapidsms.contrib.handlers import PatternHandler

class SumHandler(PatternHandler):
    pattern = r"^(\d+) plus (\d+)$"

    def handle(self, a, b):
        a, b = int(a), int(b)
        total = a + b
        self.respond("%d + %d = %d" % (a, b, total))

Your handler must define pattern and handle(*args). The pattern is case-insensitive, but must otherwise be matched precisely as written (for example, the handler pattern written above would not accept leading or trailing whitespace, but the pattern r"^(\d+) plus (\d+)\s*$" would allow trailing whitespace). When the pattern is matched, the handle method is called with the captures as arguments. As an example, the above handler could create the following conversation:

> 1 plus 2
< 1 + 2 = 3

Like KeywordHandler, each PatternHandler silently ignores all non-matching messages to allow other handlers and applications to catch them.

Here’s documentation from the PatternHandler class:

class rapidsms.contrib.handlers.PatternHandler

This handler type can be subclassed to create simple pattern-based handlers. This isn’t usually a good idea – it’s cumbersome to write patterns with enough flexibility to be used in the real world – but it’s very handy for prototyping, and can easily be upgraded later.

When a message is received, it is matched against the mandatory pattern attribute (a regular expression). If the pattern is matched, the handle method is called with the captures as arguments. For example:

>>> class SumHandler(PatternHandler):
...    pattern = r'^(\d+) plus (\d+)$'
...
...    def handle(self, a, b):
...        a, b = int(a), int(b)
...        total = a + b
...
...        self.respond(
...            "%d+%d = %d" %
...            (a, b, total))

>>> SumHandler.test("1 plus 2")
['1+2 = 3']

Note that the pattern must be matched precisely (excepting case sensitivity). For example, this would not work because of the trailing whitespace:

>>> SumHandler.test("1 plus 2 ")
False

All non-matching messages are silently ignored, to allow other apps or handlers to catch them.

handle(*args)

Called when the message matches the pattern. Any matching groups are passed to it.

Parameters:args – The matching groups from the regular expression.
pattern = None

A string specifying a regular expression that should match the message. Not case sensitive.

BaseHandler

All handlers, including the KeywordHandler and PatternHandler, are derived from the BaseHandler class. When extending from BaseHandler, one must always override the class method dispatch, which should return True when it handles a message.

All instances of BaseHandler have access to self.msg and self.router, as well as the methods self.respond and self.respond_error (which respond to the instance’s message).

BaseHandler also defines the class method test, which creates a simple environment for testing a handler’s response to a specific message text. If the handler ignores the message then False is returned. Otherwise a list containing the text property of each OutgoingMessage response, in the order which they were sent, is returned. (Note: the list may be empty.) For example:

>>> from rapidsms.contrib.echo.handlers.echo import EchoHandler
>>> EchoHandler.test("not applicable")
False
>>> EchoHandler.test("echo hello!")
["hello!"]

For an example implementation of a BaseHandler, see rapidsms.contrib.echo.handlers.ping.PingHandler.

Calling Handlers

When a message is received, the handlers application calls dispatch on each of the handlers it loaded during handlers discovery.

The first handler to accept the message will block all others. The order in which the handlers are called is not guaranteed, so each handler should be as conservative as possible when choosing to respond to a message.

Handler Discovery

Please, see the release notes

Handlers may be any new-style Python class which extends from one of the core handler classes, e.g. BaseHandler, PatternHandler, KeywordHandler, etc.

The Python package names of the handler classes to be loaded should be listed in RAPIDSMS_HANDLERS.

Example:

RAPIDSMS_HANDLERS = [
    "rapidsms.contrib.handlers.KeywordHandler",
    "rapidsms.contrib.handlers.PatternHandler",
]

Warning

The behavior described in the rest of this section is the old, deprecated behavior. If RAPIDSMS_HANDLERS is set, the older settings are ignored.

Handlers may be defined in the handlers subdirectory of any Django app listed in INSTALLED_APPS. Each file in the handlers subdirectory is expected to contain exactly one new-style Python class which extends from one of the core handler classes.

Handler discovery, which occurs when the handlers application is loaded, can be configured using the following project settings:

  • RAPIDSMS_HANDLERS_EXCLUDE_APPS - The application will not load handlers from any Django app included in this list.
  • INSTALLED_HANDLERS - If this list is not None, the application will load only handlers in modules that are included in this list.
  • EXCLUDED_HANDLERS - The application will not load any handler in a module that is included in this list.

Note

Prefix matching is used to determine which handlers are described in INSTALLED_HANDLERS and EXCLUDED_HANDLERS. The module name of each handler is compared to each value in these settings to see if it starts with the value. For example, consider the rapidsms.contrib.echo application which contains the echo handler and the ping handler:

  • “rapidsms.contrib.echo.handlers.echo” would match only EchoHandler,
  • “rapidsms.contrib.echo” would match both EchoHandler and PingHandler,
  • “rapidsms.contrib” would match all handlers in any RapidSMS contrib application, including both in rapidsms.contrib.echo.