pomo-i18n 0.1.5

Strict-typed, dependency-free gettext-compatible i18n library (PO/MO parser, Plural-Forms evaluator, Catalog API).

pomo-i18n

English | 日本語

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A minimal, strictly-typed gettext-compatible internationalization library for Python.

pomo-i18n provides .po and .mo parsing, safe plural-form evaluation, and a clean Pythonic API (gettext, ngettext, translation) — all without external dependencies.

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Features

• ✔ Parse .po and .mo files (GNU gettext format)
• ✔ Full plural-forms support (Plural-Forms: header)
• ✔ Safe plural expression evaluator (C-style → Python AST)
• ✔ Strict typing (mypy / Pylance friendly)
• ✔ Pure Python, no external libraries
• ✔ Works on Linux / macOS / Windows

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Installation

pip install pomo-i18n

Or vendor it directly:

src/
 └─ pypomo/

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Documentation

• API Reference
• Benchmark Results

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Quick Example

from pypomo.gettext import translation

t = translation(
    domain="messages",
    localedir="locales",
    languages=["en"],
)

_ = t.gettext

print(_("Hello"))
print(t.ngettext("apple", "apples", 1))
print(t.ngettext("apple", "apples", 3))

Expected directory layout:

locales/
 └─ en/
     └─ LC_MESSAGES/
         └─ messages.po

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.po Parsing

pomo-i18n contains a robust standalone .po parser:

• msgid, msgstr

• plurals ( msgid_plural, msgstr[n] )

• multiline strings

• Supports standard gettext comments:

  • # (translator comments)
  • #. (extracted comments)
  • #: (source references)
  • #, flags (parsed as regular comments; fuzzy will be supported in a future release)

• header extraction (msgid "")

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.mo Writing

Compile a Catalog into a .mo file:

from pypomo.catalog import Catalog
from pypomo.mo.writer import write_mo
from pypomo.parser.types import POEntry

entries = [
    POEntry(
        msgid="",
        msgstr=(
            "Language: en\n"
            "Plural-Forms: nplurals=2; plural=(n != 1);\n"
        ),
        msgid_plural=None,
        msgstr_plural={},
        comments=[],
    ),
    POEntry("Hello", "Hello!", None, {}, []),
]

cat = Catalog.from_po_entries(entries)
write_mo("messages.mo", cat)

The generated .mo file is fully compatible with Python’s built-in gettext.GNUTranslations.

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.mo Loading

pomo-i18n can also load GNU gettext .mo files back into a Catalog:

from pypomo.mo.loader import load_mo

cat = load_mo("messages.mo")

_ = cat.gettext
print(_("Hello"))

Features:

• verifies magic number (0x9504120E)
• parses msgid/msgstr tables
• handles plural entries correctly
• extracts Plural-Forms: from the header

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Plural Forms

pomo-i18n safely evaluates C-style plural rules:

Example:

Plural-Forms: nplurals=2; plural=(n != 1);

Russian example:

Plural-Forms: nplurals=3;
 plural=(n%10==1 && n%100!=11 ? 0 :
        n%10>=2 && n%10<=4 && (n%100<10 || n%100>=20) ? 1 : 2);

Expressions are converted to safe Python AST and evaluated with an isolated environment.

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Benchmarks

Plural-rule evaluation is optimized and supports multiple cache backends:

• none — debugging only
• weak — dict-based cache
• lru — fastest (default)

Set via environment variable:

export PYPOMO_CACHE=lru
export PYPOMO_PLURAL_CACHE_SIZE=512

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Roadmap

• Message merging & locale fallbacks
• Richer comment parsing (#, fuzzy, #. extracted tags)
• CLI utilities for generating .pot files
• Locale auto-detection helpers

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License

MIT License © 2025 Kiminori Kato

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