Python syntax for generating HTML, XML, or SVG programatically

domtree.py

from typing import Any, Dict, List, Union


def main():
    # shortcuts
    d = Dom()
    svg, circle, rect, g = d.svg, d.circle, d.rect, d.g

    print(
        svg(
            circle(x=3, y=4),
            rect(x=2, z=3)(width=100),
            g(id="hoi")(
                [circle(i=i) for i in range(4)],
            ),
        )
    )

    # Prints:
    # <svg>
    #   <circle x="3" y="4" />
    #   <rect x="2" z="3" width="100" />
    #   <g id="hoi">
    #     <circle i="0" />
    #     <circle i="1" />
    #     <circle i="2" />
    #     <circle i="3" />
    #   </g>
    # </svg>


class Node:
    tag: str
    children: List["Node"]
    attributes: Dict[str, Any]

    def __init__(self, tag: str):
        self.tag = tag
        self.children = []
        self.attributes = {}

    def __call__(
        self, *children: Union["Node", List["Node"]], **attributes: Any
    ) -> "Node":
        if len(self.children) > 0 and len(children) > 0:
            raise RuntimeError(
                "Cannot add children to a node that already has children"
            )
        new_node = Node(self.tag)
        new_node.children = _flatten(list(children))
        new_node.attributes = {**self.attributes, **attributes}
        return new_node

    def __str__(self):
        attr_string = "".join(
            [f' {key}="{value}"' for key, value in self.attributes.items()]
        )
        if self.children:
            child_string = "\n".join([_indent(str(c), "  ") for c in self.children])
            return f"<{self.tag}{attr_string}>\n{child_string}\n</{self.tag}>"
        else:
            return f"<{self.tag}{attr_string} />"


class Dom:
    def __getattr__(self, attr):
        return Node(attr)


def _flatten(x: List) -> List:
    r = []
    for y in x:
        if isinstance(y, list):
            r.extend(_flatten(y))
        else:
            r.append(y)
    return r


def _indent(x: str, indentation: str = "\t") -> str:
    return "".join([indentation + l for l in x.splitlines(keepends=True)])


if __name__ == "__main__":
    main()