Customizing one instance

@Renderer.register(...) changes a renderer class and every instance created from it. To change one renderer object only, call register_handler on the instance. It takes the same classifiers as register.

"""Per-instance customization: one MarkdownRenderer that hides import lines."""
from handcalcs.renderers import MarkdownRenderer


def hide_import(renderer, node, base_context):
    return ""


def make_renderer():
    renderer = MarkdownRenderer()
    renderer.register_handler("import", hide_import)
    return renderer

import math
a = 2
b = math.sqrt(a)

Output (MarkdownRenderer)

Rendered

\[\begin{aligned} a &= 2 \\ b &= \sqrt{a} = \sqrt{2} = 1.4142 \end{aligned}\]

Markdown output

$$\begin{aligned} a &= 2 \\ b &= \sqrt{a} = \sqrt{2} = 1.4142 \end{aligned}$$

Other MarkdownRenderer objects still show imports.

When to use it

• Quick experiments in a notebook, without defining a class.

• Per-request settings in an application, where each request builds its own renderer.

• Tests, where a handler must not leak into other tests.

For anything you reuse, a subclass is clearer: it has a name, can be selected in Jupyter, and can be imported from your own package.

How it works

Each renderer instance copies its class’s handler and rule tables when it is created, and register_handler adds to the copies. Registering a bare node type ("import") replaces that node’s handler; registering a rule ("import:post") appends to that node’s rule list. Instances created before a class-level register call keep the old tables.

Next: the cookbook, for complete recipes.