docs/examples/inline_gettext_extension.py

import re

from jinja2.exceptions import TemplateSyntaxError
from jinja2.ext import Extension
from jinja2.lexer import count_newlines
from jinja2.lexer import Token


_outside_re = re.compile(r"\\?(gettext|_)\(")
_inside_re = re.compile(r"\\?[()]")


class InlineGettext(Extension):
    """This extension implements support for inline gettext blocks::

        <h1>_(Welcome)</h1>
        <p>_(This is a paragraph)</p>

    Requires the i18n extension to be loaded and configured.
    """

    def filter_stream(self, stream):
        paren_stack = 0

        for token in stream:
            if token.type != "data":
                yield token
                continue

            pos = 0
            lineno = token.lineno

            while 1:
                if not paren_stack:
                    match = _outside_re.search(token.value, pos)
                else:
                    match = _inside_re.search(token.value, pos)
                if match is None:
                    break
                new_pos = match.start()
                if new_pos > pos:
                    preval = token.value[pos:new_pos]
                    yield Token(lineno, "data", preval)
                    lineno += count_newlines(preval)
                gtok = match.group()
                if gtok[0] == "\\":
                    yield Token(lineno, "data", gtok[1:])
                elif not paren_stack:
                    yield Token(lineno, "block_begin", None)
                    yield Token(lineno, "name", "trans")
                    yield Token(lineno, "block_end", None)
                    paren_stack = 1
                else:
                    if gtok == "(" or paren_stack > 1:
                        yield Token(lineno, "data", gtok)
                    paren_stack += -1 if gtok == ")" else 1
                    if not paren_stack:
                        yield Token(lineno, "block_begin", None)
                        yield Token(lineno, "name", "endtrans")
                        yield Token(lineno, "block_end", None)
                pos = match.end()

            if pos < len(token.value):
                yield Token(lineno, "data", token.value[pos:])

        if paren_stack:
            raise TemplateSyntaxError(
                "unclosed gettext expression",
                token.lineno,
                stream.name,
                stream.filename,
            )