Custom BBCode placeholders

When you define bbcode tags, you can choose to use placeholders in order to define where data is required. These placeholders, such as {TEXT} or {NUMBER} are typed. This means that some semantic verifications are done before rendering in order to ensure that the content corresponding to a specific placeholder is valid. Django-precise-bbcode comes with some built-in BBCode placeholders that you can use in your bbcode tag definitions. You can also choose to create your owns.

Built-in placeholders

Placeholder Usage Definition
{TEXT}   matches anything
{SIMPLETEXT}  

matches latin characters, numbers, spaces,

commas, dots, minus, plus, hyphen and underscore

{COLOR}   matches a colour (eg. red or #000FFF)
{NUMBER}   matches a number
{URL}   matches a valid URL
{EMAIL}   matches a valid e-mail address
{RANGE} {RANGE=min,max} matches a valid number between min and max
{CHOICE} {CHOICE=foo,bar}

matches all strings separated with commas in the

placeholder

Defining BBCode placeholders plugins

Django-precise-bbcode allows you to define your own placeholders.

To do so, you will have to write a subclass of precise_bbcode.bbcode.placeholder.BBCodePlaceholder for any placeholder you want to create. These class-based bbcode placeholders must be defined inside a bbcode_placeholders Python module in your Django application (just add a file called bbcode_placeholders.py to an existing Django application). In the same way as bbcode tag classes, your class-based bbcode placeholders must be registered to the precise_bbcode.placeholder_pool.placeholder_pool object by using its register_placeholder method to be available to the BBCode parser.

Each bbcode placeholder must have a name attribute and can operate in two different ways:

  • The BBCodePlaceholder subclass provides a pattern attribute, which is a valid regular expression. In this case, a given content will be valid in the context of the placeholder if it matches this regular expression
  • The BBCodePlaceholder subclass implements a validate method. This method is used to check whether a given content is valid according to the placeholder definition associated to it and should return True or False

Defining placeholders based on a regular expression pattern

In this case, you have to provide a pattern attribute to your BBCodePlaceholder subclass, in addition to the name attribute.

Let’s write a simple example. Consider we are trying to write a {PHONENUMBER} bbcode placeholder which will allow end-users to fill some bbcode tags with phone numbers. So we could write:

# bbcode_placeholders.py
import re
from precise_bbcode.bbcode.placeholder import BBCodePlaceholder
from precise_bbcode.placeholder_pool import placeholder_pool

class PhoneNumberBBCodePlaceholder(BBCodePlaceholder):
    name = 'phonenumber'
    pattern = re.compile(r'(\d{3}[-\.\s]??\d{3}[-\.\s]??\d{4}|\(\d{3}\)\s*\d{3}[-\.\s]??\d{4}|\d{3}[-\.\s]??\d{4})')

placeholder_pool.register_placeholder(PhoneNumberBBCodePlaceholder)

So if this placeholder is used inside, let’s say, a [telto] bbcode tag, +33000000000 will be a valid input.

Defining placeholders based on a validate method

In this case, each of your BBCodePlaceholder subclasses must provide a name attribute and must implement a validate method. This method is used to check whether the input associated with a placeholder is valid and can be rendered. The validate method takes two arguments:

  • content: the content used to fill the placeholder that must be validated
  • extra_context: the extra context of the placeholder if defined in a tag definition

Note that the extra context is a string defined in the placeholder in a bbcode tag definition. For example, CHOICE is the placeholder name and apple,tomato is the extra context if the CHOICE placeholder is used as follows inside a bbcode tag definition: {CHOICE=apple,tomato}.

Let’s write an example. Consider we are trying to write a {RANGE} placeholder which will allow end-users to fill some bbcode tags with a number that will be valid only if it is within a specific range. So we could write:

# bbcode_placeholders.py
import re
from precise_bbcode.bbcode.placeholder import BBCodePlaceholder
from precise_bbcode.placeholder_pool import placeholder_pool

class RangeBBCodePlaceholder(BBCodePlaceholder):
    name = 'range'

    def validate(self, content, extra_context):
        try:
            value = float(content)
        except ValueError:
            return False

        try:
            min_content, max_content = extra_context.split(',')
            min_value, max_value = float(min_content), float(max_content)
        except ValueError:
            return False

        if not (value >= min_value and value <= max_value):
            return False

    return True


placeholder_pool.register_placeholder(RangeBBCodePlaceholder)

The validate method allows you to implement your own validation logic for your custom placeholders.

Overriding default BBCode placeholders

When loaded, the parser provided by django-precise-bbcode provides some default bbcode placeholders (please refer to Built-in placeholders for the full list of default placeholders). These default placeholders can be overridden. You just have to register another placeholder with the same name and it will override the default one.