py4web template language formatter using djlint

py4web_template_formatter.md

A script which formats py4web templates using DJLint, by partially converting them to Django syntax and back.

How to use:

1. Install DJLint: py -m pip install djlint
2. Download the script
3. Run the script with a template file: py template_formatter.py ./templates/mytemplate.html

Auto-format on save in VSCode:

1. Get the Run On Save extension
2. If you have a venv, configure it like this. (assumes venv is located in: ./.venv - if its not, or on another OS, adjust paths accordingly.)

"emeraldwalk.runonsave": {
  "commands": [
    {
      "match": ".*\\.html$",
      "cmd": "\"${workspaceFolder}/.venv/Scripts/python.exe\" \"${workspaceFolder}/template_formatter.py\" \"${file}\""
    }
  ]
},

Configuring djlint: I have this config in my pyproject.toml - consult djlint docs for which other configs are available

[tool.djlint]
format_js = true
indent = 2

[tool.djlint.js]
indent_size = 2
break_chained_methods = true

template_formatter.py

"""Formats py4web templates
It does this by converting their syntax to Django
using djlint to format, and converting them back

MIT license:
Copyright 2025 laund
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE."""

import argparse
import re
import typing
from pathlib import Path

import djlint
import djlint.formatter
import djlint.reformat

INBRACKETS_ADD = re.compile(
    r"(?P<indent>^[ \t]*)(?!\n)(?P<open>\[\[)?(?P<text>.*)(?<!\])(?P<close>\]?\]?)",
    re.MULTILINE,
)


def multiline_fixer_inner(match: re.Match[str]) -> str:
    gd = match.groupdict()

    opening = "{%" if gd["open"] else "{%-"
    closing = "%}" if gd["close"] else "-%}"

    return f"{gd['indent']}{opening} {gd['text']} {closing}"


def multilinefixer(match: re.Match[str]) -> str:
    inp = match.group()
    res = INBRACKETS_ADD.sub(multiline_fixer_inner, inp)
    return res


PY4WEB_TO_DJANGO = [
    (re.compile(r"\[\[(.*?)\]\]", flags=re.DOTALL), multilinefixer),
    (re.compile(r"\[\[(-?) ?def(.*?): ?(-?)\]\]"), r"{%\1 def\2:def \3%}"),
    (re.compile(r"{%(-?) ?end ?(-?)%}"), r"{%\1 endblock \2%}"),
    (re.compile(r"{%(-?) ?return ?(-?)%}"), r"{%\1 enddef \2%}"),
    (re.compile(r"{%(-?) ?pass ?(-?)%}"), r"{%\1 end \2%}"),
]

DJANGO_TO_PY4WEB = [
    (re.compile(r"{%(-?) ?endblock ?(-?)%}"), r"{%\1 end \2%}"),
    (re.compile(r"{%(-?) ?enddef ?(-?)%}"), r"{%\1 return \2%}"),
    (re.compile(r"{%(-?) ?end ?(-?)%}"), r"{%\1 pass \2%}"),
    (re.compile(r"({%-? ?def.*?):def( ?-?%})"), r"\1:\2"),
    (re.compile(r"{%- ?"), ""),
    (re.compile(r" ?-%}"), ""),
    (re.compile(r"{% ?(.*?) ?%}", flags=re.DOTALL), r"[[\1]]"),
    (re.compile(r"(^\s)*{% ?", flags=re.MULTILINE), r"\1[["),
    (re.compile(r" ?%}\s*$", flags=re.MULTILINE), "]]"),
]


def file_arg(arg: str):
    path = Path(arg)
    if not path.exists():
        raise ValueError("Path not found")
    if path.is_dir():
        raise ValueError("Path is a folder")
    return path


def main():
    inject_jschain()  # monkey-patch PR: https://github.com/beautifier/js-beautify/pull/2344
    parser = argparse.ArgumentParser(description="Format py4web templates")
    parser.add_argument("filepath", type=file_arg, help="Path to file")
    args = parser.parse_args()

    filepath: Path = args.filepath

    with filepath.open(encoding="utf-8") as f:
        rawcode = f.read()

    for pat, templ in PY4WEB_TO_DJANGO:
        rawcode = pat.sub(templ, rawcode)
    config = djlint.Config(
        "-",
        custom_blocks="def",
        blank_line_before_tag="def,block",
        blank_line_after_tag="from,include,import,extend,return",
    )
    # if someone set break_chained_methods without wrap_line_length,
    # set wrap_line_length here for the monkey-patched method-chain wrapping
    # code to work.
    if (
        config.js_config.get("break_chained_methods")
        and config.js_config.get("wrap_line_length", 0) == 0
    ):
        # if not explicitly set, assume js will be indented 2 indents
        config.js_config["wrap_line_length"] = (
            config.max_line_length - config.indent_size * 2
        )
    formatted = djlint.reformat.formatter(config, rawcode)
    for pat, templ in DJANGO_TO_PY4WEB:
        formatted = pat.sub(templ, formatted)

    with filepath.open("w", encoding="utf-8") as f:
        f.write(formatted)


def inject_jschain():
    """monkey-path jsbeautifier for better function-chain formatting
    specifically, this breaks all calls in function-chains if any one of them would
    need to be broken to stay in line length"""
    # might break with djlint/jsbeautifier update, in that case just keep old behaviour.
    try:
        from jsbeautifier.javascript.beautifier import (
            TOKEN,
            Beautifier,
            _special_word_set,
            reserved_array,
        )

        _peek_lloc_stop = [TOKEN.SEMICOLON, TOKEN.END_BLOCK, TOKEN.EOF, TOKEN.RESERVED]

        @typing.no_type_check
        def guess_current_lloc_len(self: Beautifier):
            """Try to guess how long, in chars, this lloc would be if it was condensed to a single line."""

            # empty string is the "separator" between forwards and backwards
            txts = [""]

            # lookbehind loop
            while True:
                bak_token = self._tokens.peek(-len(txts))
                if bak_token is None:
                    break
                if bak_token.type in [*_peek_lloc_stop, TOKEN.START_BLOCK]:
                    break
                txts.append(bak_token.text)

            # since we looped backwards, reverse the gathered texts here
            txts = list(reversed(txts))

            bak_tokens = len(txts)
            # lookahead loop
            while True:
                fwd_token = self._tokens.peek(len(txts) - bak_tokens)
                if fwd_token is None:
                    break
                if fwd_token.type in _peek_lloc_stop:
                    break
                txts.append(fwd_token.text)

            line = "".join(txts)
            # print(len(line), line)

            cur_line = self._output.current_line.toString()
            indent_chars = len(cur_line) - len(cur_line.lstrip())
            return len(line) + indent_chars

        @typing.no_type_check
        def handle_dot(self: Beautifier, current_token):
            if self.start_of_statement(current_token):
                # The conditional starts the statement if appropriate.
                pass
            else:
                self.handle_whitespace_and_comments(current_token, True)

            if re.search("^([0-9])+$", self._flags.last_token.text):
                self._output.space_before_token = True

            if reserved_array(self._flags.last_token, _special_word_set):
                self._output.space_before_token = False
            else:
                # allow preserved newlines before dots in general
                # force newlines on dots after close paren when break_chained - for
                # bar().baz()
                self.allow_wrap_or_preserved_newline(
                    current_token,
                    (
                        0
                        < self._options.wrap_line_length
                        < guess_current_lloc_len(self)
                        or self._flags.last_token.text == ")"
                    )
                    and self._options.break_chained_methods,
                )

            # Only unindent chained method dot if this dot starts a new line.
            # Otherwise the automatic extra indentation removal
            # will handle any over indent
            if (
                self._options.unindent_chained_methods
                and self._output.just_added_newline()
            ):
                self.deindent()

            self.print_token(current_token)

        Beautifier.handle_dot = handle_dot
    except Exception as e:
        print(f"didn't inject js-beautifier due to: {e}")


if __name__ == "__main__":
    main()