Limnoria-doc/develop/using_wrap.rst

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Using commands.wrap to parse your command's arguments
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This document illustrates how to use the new 'wrap' function present in Supybot
0.80 to handle argument parsing and validation for your plugin's commands.

Introduction
============
To plugin developers for older (pre-0.80) versions of Supybot, one of the more
annoying aspects of writing commands was handling the arguments that were
passed in. In fact, many commands often had to duplicate parsing and
verification code, resulting in lots of duplicated code for not a whole lot of
action. So, instead of forcing plugin writers to come up with their own ways of
cleaning it up, we wrote up the wrap function to handle all of it.

It allows a much simpler and more flexible way of checking things than before
and it doesn't require that you know the bot internals to do things like check
and see if a user exists, or check if a command name exists and whatnot.

If you are a plugin author this document is absolutely required reading, as it
will massively ease the task of writing commands.

Using Wrap
==========
First off, to get the wrap function, it is recommended (strongly) that you use
the following import line::

   from supybot.commands import *

This will allow you to access the wrap command (and it allows you to do it
without the commands prefix). Note that this line is added to the imports of
plugin templates generated by the supybot-plugin-create script.

Let's write a quickie command that uses wrap to get a feel for how it makes our
lives better. Let's write a command that repeats a string of text a given
number of times. So you could say "repeat 3 foo" and it would say "foofoofoo".
Not a very useful command, but it will serve our purpose just fine. Here's how
it would be done without wrap::

   def repeat(self, irc, msg, args):
       """<num> <text>

       Repeats <text> <num> times.
       """
       (num, text) = privmsg.getArgs(args, required=2)
       try:
           num = int(num)
       except ValueError:
           raise callbacks.ArgumentError
       irc.reply(num * text)

Note that all of the argument validation and parsing takes up 5 of the 6 lines
(and you should have seen it before we had privmsg.getArgs!). Now, here's what
our command will look like with wrap applied::

   def repeat(self, irc, msg, args, num, text):
       """<num> <text>

       Repeats <text> <num> times.
       """
       irc.reply(text * num)
   repeat = wrap(repeat, ['int', 'text'])

Pretty short, eh? With wrap all of the argument parsing and validation is
handled for us and we get the arguments we want, formatted how we want them,
and converted into whatever types we want them to be - all in one simple
function call that is used to wrap the function! So now the code inside each
command really deals with how to execute the command and not how to deal with
the input.

So, now that you see the benefits of wrap, let's figure out what stuff we have
to do to use it.

Syntax Changes
==============
There are two syntax changes to the old style that are implemented. First, the
definition of the command function must be changed. The basic syntax for the
new definition is::

   def commandname(self, irc, msg, args, <arg1>, <arg2>, ...):

Where arg1 and arg2 (up through as many as you want) are the variables that
will store the parsed arguments. "Now where do these parsed arguments come
from?" you ask. Well, that's where the second syntax change comes in. The
second syntax change is the actual use of the wrap function itself to decorate
our command names. The basic decoration syntax is::

   commandname = wrap(commandname, [converter1, converter2, ...])

.. note::

  This should go on the line immediately following the body of the command's
  definition, so it can easily be located (and it obviously must go after the
  command's definition so that commandname is defined).

Each of the converters in the above listing should be one of the converters in
commands.py (I will describe each of them in detail later.) The converters are
applied in order to the arguments given to the command, generally taking
arguments off of the front of the argument list as they go. Note that each of
the arguments is actually a string containing the NAME of the converter to use
and not a reference to the actual converter itself. This way we can have
converters with names like int and not have to worry about polluting the
builtin namespace by overriding the builtin int.

As you will find out when you look through the list of converters below, some
of the converters actually take arguments. The syntax for supplying them (since
we aren't actually calling the converters, but simply specifying them), is to
wrap the converter name and args list into a tuple. For example::

 commandname = wrap(commandname, [(converterWithArgs, arg1, arg2),
                                  converterWithoutArgs1, converterWithoutArgs2])

For the most part you won't need to use an argument with the converters you use
either because the defaults are satisfactory or because it doesn't even take
any.

Customizing Wrap
================
Converters alone are a pretty powerful tool, but for even more advanced (yet
simpler!) argument handling you may want to use contexts. Contexts describe how
the converters are applied to the arguments, while the converters themselves
do the actual parsing and validation.

For example, one of the contexts is "optional". By using this context, you're
saying that a given argument is not required, and if the supplied converter
doesn't find anything it likes, we should use some default. Yet another
example is the "reverse" context. This context tells the supplied converter to
look at the last argument and work backwards instead of the normal
first-to-last way of looking at arguments.

So, that should give you a feel for the role that contexts play. They are not
by any means necessary to use wrap. All of the stuff we've done to this point
will work as-is. However, contexts let you do some very powerful things in very
easy ways, and are a good thing to know how to use.

Now, how do you use them? Well, they are in the global namespace of
src/commands.py, so your previous import line will import them all; you can
call them just as you call wrap. In fact, the way you use them is you simply
call the context function you want to use, with the converter (and its
arguments) as arguments. It's quite simple. Here's an example::

   commandname = wrap(commandname, [optional('int'), many('something')])

In this example, our command is looking for an optional integer argument first.
Then, after that, any number of arguments which can be anything (as long as
they are something, of course).

Do note, however, that the type of the arguments that are returned can be
changed if you apply a context to it. So, optional("int") may very well return
None as well as something that passes the "int" converter, because after all
it's an optional argument and if it is None, that signifies that nothing was
there. Also, for another example, many("something") doesn't return the same
thing that just "something" would return, but rather a list of "something"s.

Converter List
==============
Below is a list of all the available converters to use with wrap. If the
converter accepts any arguments, they are listed after it and if they are
optional, the default value is shown.

id, kind="integer"

    Returns something that looks like an integer ID number. Takes an optional
    "kind" argument for you to state what kind of ID you are looking for,
    though this doesn't affect the integrity-checking. Basically requires that
    the argument be an integer, does no other integrity-checking, and provides
    a nice error message with the kind in it.

ip

    Checks and makes sure the argument looks like a valid IP and then returns
    it.

int, type="integer", p=None

    Gets an integer. The "type" text can be used to customize the error message
    received when the argument is not an integer. "p" is an optional predicate
    to test the integer with. If p(i) fails (where i is the integer arg parsed
    out of the argument string), the arg will not be accepted.

index

    Basically ("int", "index"), but with a twist. This will take a 1-based
    index and turn it into a 0-based index (which is more useful in code). It
    doesn't transform 0, and it maintains negative indices as is (note that it
    does allow them!).

color

    Accepts arguments that describe a text color code (e.g., "black", "light
    blue") and returns the mIRC color code for that color. (Note that many
    other IRC clients support the mIRC color code scheme, not just mIRC)

now

    Simply returns the current timestamp as an arg, does not reference or
    modify the argument list.

url

    Checks for a valid URL.

httpUrl

    Checks for a valid HTTP URL.

long, type="long"

    Basically the same as int minus the predicate, except that it converts the
    argument to a long integer regardless of the size of the int.

float, type="floating point number"

    Basically the same as int minus the predicate, except that it converts the
    argument to a float.

nonInt, type="non-integer value"

    Accepts everything but integers, and returns them unchanged. The "type"
    value, as always, can be used to customize the error message that is
    displayed upon failure.

positiveInt

    Accepts only positive integers.

nonNegativeInt

    Accepts only non-negative integers.

letter

    Looks for a single letter. (Technically, it looks for any one-element
    sequence).

haveOp, action="do that"

    Simply requires that the bot have ops in the channel that the command is
    called in. The action parameter completes the error message: "I need to be
    opped to ...".

expiry

    Takes a number of seconds and adds it to the current time to create an
    expiration timestamp.

literal, literals, errmsg=None

    Takes a required sequence or string (literals) and any argument that
    uniquely matches the starting substring of one of the literals is
    transformed into the full literal. For example, with ``("literal", ("bar",
    "baz", "qux"))``, you'd get "bar" for "bar", "baz" for "baz", and "qux"
    for any of "q", "qu", or "qux". "b" and "ba" would raise errors because
    they don't uniquely identify one of the literals in the list. You can
    override errmsg to provide a specific (full) error message, otherwise the
    default argument error message is displayed.

to

    Returns the string "to" if the arg is any form of "to" (case-insensitive).

nick

    Checks that the arg is a valid nick on the current IRC server.

seenNick

    Checks that the arg is a nick that the bot has seen (NOTE: this is limited
    by the size of the history buffer that the bot has).

channel

    Gets a channel to use the command in. If the channel isn't supplied, uses
    the channel the message was sent in. If using a different channel, does
    sanity-checking to make sure the channel exists on the current IRC network.

inChannel

    Requires that the command be called from within any channel that the bot
    is currently in or with one of those channels used as an argument to the
    command.

onlyInChannel

    Requires that the command be called from within any channel that the bot
    is currently in.

nickInChannel

    Requires that the argument be a nick that is in the current channel, and
    returns that nick.

networkIrc, errorIfNoMatch=False

    Returns the IRC object of the specified IRC network. If one isn't
    specified, the IRC object of the IRC network the command was called on is
    returned.

callerInGivenChannel

    Takes the given argument as a channel and makes sure that the caller is in
    that channel.

plugin, require=True

    Returns the plugin specified by the arg or None. If require is True, an
    error is raised if the plugin cannot be retrieved.

boolean

    Converts the text string to a boolean value. Acceptable true values are:
    "1", "true", "on", "enable", or "enabled" (case-insensitive). Acceptable
    false values are: "0", false", "off", "disable", or "disabled"
    (case-insensitive).

lowered

    Returns the argument lowered (NOTE: it is lowered according to IRC
    conventions, which does strange mapping with some punctuation characters).

anything

    Returns anything as is.

something, errorMsg=None, p=None

    Takes anything but the empty string. errorMsg can be used to customize the
    error message. p is any predicate function that can be used to test the
    validity of the input.

filename

    Used to get a filename argument.

commandName

    Returns the canonical command name version of the given string (ie, the
    string is lowercased and dashes and underscores are removed).

text

    Takes the rest of the arguments as one big string. Note that this differs
    from the "anything" context in that it clobbers the arg string when it's
    done.  Using any converters after this is most likely incorrect.

glob

    Gets a glob string. Basically, if there are no wildcards (``*``, ``?``) in
    the argument, returns ``*string*``, making a glob string that matches
    anything containing the given argument.

somethingWithoutSpaces

    Same as something, only with the exception of disallowing spaces of course.

capability

    Used to retrieve an argument that describes a capability.

channelDb

    Sets the channel appropriately in order to get to the databases for that
    channel (handles whether or not a given channel uses channel-specific
    databases and whatnot).

hostmask

    Returns the hostmask of any provided nick or hostmask argument.

banmask

    Returns a generic banmask of the provided nick or hostmask argument.

user

    Requires that the caller be a registered user.

matches, regexp, errmsg

    Searches the args with the given regexp and returns the matches. If no
    match is found, errmsg is given.

public

    Requires that the command be sent in a channel instead of a private
    message.

private

    Requires that the command be sent in a private message instead of a
    channel.

otherUser

    Returns the user specified by the username or hostmask in the argument.

regexpMatcher

    Gets a matching regexp argument (m// or //).

validChannel

    Gets a channel argument once it makes sure it's a valid channel.

regexpReplacer

    Gets a replacing regexp argument (s//).

owner

    Requires that the command caller has the "owner" capability.

admin

    Requires that the command caller has the "admin" capability.

checkCapability, capability

    Checks to make sure that the caller has the specified capability.

checkChannelCapability", capability
    Checks to make sure that the caller has the specified capability on the
    channel the command is called in.

Contexts List
=============
  What contexts are available for me to use?

The list of available contexts is below. Unless specified otherwise, it can be
assumed that the type returned by the context itself matches the type of the
converter it is applied to.

any
    Looks for any number of arguments matching the supplied converter. Will
    return a sequence of converted arguments or None.

many
    Looks for multiple arguments matching the supplied converter. Expects at
    least one to work, otherwise it will fail. Will return the sequence of
    converted arguments.

optional
    Look for an argument that satisfies the supplied converter, but if it's not
    the type I'm expecting or there are no arguments for us to check, then use
    the default value. Will return the converted argument as is or None.

additional
    Look for an argument that satisfies the supplied converter, making sure
    that it's the right type. If there aren't any arguments to check, then use
    the default value. Will return the converted argument as is or None.

rest
    Treat the rest of the arguments as one big string, and then convert. If the
    conversion is unsuccessful, restores the arguments.

getopts
    Handles --option style arguments. Each option should be a key in a
    dictionary that maps to the name of the converter that is to be used on
    that argument. To make the option take no argument, use "" as the converter
    name in the dictionary. For no conversion, use None as the converter name
    in the dictionary.

first
    Tries each of the supplied converters in order and returns the result of
    the first successfully applied converter.

reverse
    Reverse the argument list, apply the converters, and then reverse the
    argument list back.

commalist
    Looks for a comma separated list of arguments that match the supplied
    converter. Returns a list of the successfully converted arguments. If any
    of the arguments fail, this whole context fails.


Final Word
==========

Now that you know how to use wrap, and you have a list of converters and
contexts you can use, your task of writing clean, simple, and safe plugin code
should become much easier. Enjoy!