[python] Implement basic use-mojo-in-python that exposes decimo to Python via `_decimo.so` by forfudan · Pull Request #179 · forfudan/decimo

forfudan · 2026-03-02T19:12:38Z

Adds an initial “use mojo in python” proof-of-concept that exposes Decimo’s BigDecimal to Python via a Mojo-built CPython extension module (_decimo.so), with a thin Python wrapper (decimo.Decimal) providing Pythonic dunder/operator behavior. The PR also reorganizes shell test runners, integrates Python formatting (ruff) into tooling, and expands CI into parallel jobs.

Changes:

Introduces python/decimo_module.mojo (_decimo extension), python/decimo.py (Python wrapper), and Python-side tests/stubs.
Refactors tests/test_all.sh into smaller test runners and adds a top-level tests/test_decimo.sh aggregator.
Updates pixi.toml, pre-commit, and GitHub Actions workflow to incorporate the new Python flow and formatting.

Copilot

Pull request overview

Adds an initial “mojo4py” proof-of-concept that exposes Decimo’s BigDecimal to Python via a Mojo-built CPython extension module (_decimo.so), with a thin Python wrapper (decimo.Decimal) providing Pythonic dunder/operator behavior. The PR also reorganizes shell test runners, integrates Python formatting (ruff) into tooling, and expands CI into parallel jobs.

Changes:

Introduces python/decimo_module.mojo (_decimo extension), python/decimo.py (Python wrapper), and Python-side tests/stubs.
Refactors tests/test_all.sh into smaller test runners and adds a top-level tests/test_decimo.sh aggregator.
Updates pixi.toml, pre-commit, and GitHub Actions workflow to incorporate the new Python flow and formatting.

Reviewed changes

Copilot reviewed 20 out of 22 changed files in this pull request and generated 8 comments.

Show a summary per file

File	Description
tests/test_tomlmojo.sh	Simplifies the TOMLMojo test runner.
tests/test_decimo.sh	New aggregator script to run decimo-related Mojo test suites.
tests/test_decimal128.sh	New Decimal128 test runner script.
tests/test_binary.sh	Removed legacy script in favor of per-suite runners.
tests/test_biguint.sh	New BigUInt test runner script.
tests/test_bigint10.sh	New BigInt10 test runner script.
tests/test_bigint.sh	New BigInt test runner script.
tests/test_bigdecimal.sh	New BigDecimal test runner script.
tests/test_big.sh	Removed legacy script in favor of per-suite runners.
tests/test_all.sh	Now delegates to the new suite-level runners.
tests/cli/test_evaluator.mojo	Updates docstrings in evaluator tests.
python/tests/test_decimo.py	Adds Python “Phase 0” interop tests for the wrapper/extension.
python/decimo_module.mojo	Adds Mojo bindings to build the `_decimo` CPython extension module.
python/decimo.py	Adds the Python `Decimal` wrapper delegating to the `_decimo` extension.
python/_decimo.pyi	Adds type stubs for the `_decimo` extension API.
pixi.toml	Adds Python build/test tasks and ruff formatting; reorganizes tasks.
pixi.lock	Locks the added `ruff` dependency.
docs/plans/mojo4py.md	Adds a detailed design/roadmap document for Mojo→Python bindings.
LICENSE	Replaces the Apache template placeholder copyright line.
.pre-commit-config.yaml	Splits formatting hooks: Mojo format for `.mojo`, ruff for `.py`.
.gitignore	Ignores Python build artifacts (`.so`, `__pycache__`, `.pyc`).
.github/workflows/run_tests.yaml	Reworks CI into parallel jobs and adds Python/format checks.

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Copilot · 2026-03-02T19:19:14Z

.github/workflows/run_tests.yaml

+      - name: Build CLI binary
+        run: pixi run buildcli
      - name: Run tests
+        run: bash ./tests/test_cli.sh


The workflow runs pixi run build, but pixi.toml no longer defines a build task (it defines buildcli). This step will fail at runtime unless build is reintroduced or the workflow is updated to call the new task name.

Copilot · 2026-03-02T19:19:15Z

.github/workflows/run_tests.yaml

+      - name: Build & run Python tests
+        run: pixi run testpy



The workflow runs pixi run pytest, but pixi.toml does not define a pytest task (it defines testpy). This job will fail unless the task name is aligned (either add a pytest task/alias or update the workflow to run the existing Python test task).

Copilot · 2026-03-02T19:19:15Z

python/decimo.py

+        return not self._inner.lt(other._inner)
+
+    def __ne__(self, other):
+        return not self.__eq__(other)


__ne__ is implemented as not self.__eq__(other). If __eq__ returns NotImplemented (e.g., comparing to an unconvertible type), this will incorrectly return False instead of propagating NotImplemented. Handle the NotImplemented case explicitly or implement __ne__ via the underlying _inner comparison.

Suggested change

return not self.__eq__(other)

eq_result = self.__eq__(other)

if eq_result is NotImplemented:

return NotImplemented

return not eq_result

Copilot · 2026-03-02T19:19:15Z

python/decimo.py

+    def __bool__(self):
+        return str(self) != "0"
+


__bool__ currently checks str(self) != "0", but decimo can stringify negative zero as "-0" (noted in the Python tests), which would incorrectly evaluate as truthy. Consider implementing truthiness using a numeric comparison to zero (e.g., via _inner.eq(...)) or normalizing the string check to treat both "0" and "-0" as false.

Copilot · 2026-03-02T19:19:16Z

python/decimo.py

+            other = Decimal(other)
+        return self._inner.lt(other._inner)
+
+    def __le__(self, other):
+        if not isinstance(other, Decimal):
+            other = Decimal(other)
+        return self._inner.le(other._inner)
+
+    def __gt__(self, other):
+        if not isinstance(other, Decimal):
+            other = Decimal(other)
+        return not self._inner.le(other._inner)
+
+    def __ge__(self, other):
+        if not isinstance(other, Decimal):
+            other = Decimal(other)


__lt__/__le__/__gt__/__ge__ eagerly coerce other to Decimal and will raise if conversion fails, unlike __eq__ which returns NotImplemented on unconvertible inputs. For Python operator semantics (and to allow the reflected comparison to run), these methods should also return NotImplemented when other cannot be converted.

Suggested change

other = Decimal(other)

return self._inner.lt(other._inner)

def __le__(self, other):

if not isinstance(other, Decimal):

other = Decimal(other)

return self._inner.le(other._inner)

def __gt__(self, other):

if not isinstance(other, Decimal):

other = Decimal(other)

return not self._inner.le(other._inner)

def __ge__(self, other):

if not isinstance(other, Decimal):

other = Decimal(other)

try:

other = Decimal(other)

except Exception:

return NotImplemented

return self._inner.lt(other._inner)

def __le__(self, other):

if not isinstance(other, Decimal):

try:

other = Decimal(other)

except Exception:

return NotImplemented

return self._inner.le(other._inner)

def __gt__(self, other):

if not isinstance(other, Decimal):

try:

other = Decimal(other)

except Exception:

return NotImplemented

return not self._inner.le(other._inner)

def __ge__(self, other):

if not isinstance(other, Decimal):

try:

other = Decimal(other)

except Exception:

return NotImplemented

Copilot · 2026-03-02T19:19:16Z

python/decimo_module.mojo

+from python import PythonObject, Python
+from python.bindings import PythonModuleBuilder
+from os import abort
+from memory import UnsafePointer


Python and UnsafePointer are imported but not used in this module. Removing unused imports will keep the binding module minimal and avoid potential lint/compile warnings as the Mojo toolchain evolves.

Suggested change

from python import PythonObject, Python

from python.bindings import PythonModuleBuilder

from os import abort

from memory import UnsafePointer

from python import PythonObject

from python.bindings import PythonModuleBuilder

from os import abort

Copilot · 2026-03-02T19:19:17Z

pixi.toml

-test_cli = "bash tests/test_cli.sh"
+bcli = "clear && pixi run buildcli"
+buildcli = "pixi run mojo build -I src -I src/cli -o decimo src/cli/main.mojo"
+tcli = "clear && pixi run clitest"


bcli and tcli call clibuild/clitest, but only buildcli and testcli are defined below. As written, pixi run bcli / pixi run tcli will fail with an unknown task; either rename buildcli→clibuild and testcli→clitest, or update bcli/tcli to reference the existing task names.

Suggested change

tcli = "clear && pixi run clitest"

tcli = "clear && pixi run testcli"

Copilot · 2026-03-02T19:19:17Z

pixi.toml

+bpy = "clear && pixi run buildpy"
+buildpy = """pixi run mojo build python/decimo_module.mojo \
+--emit shared-lib -I src -o python/_decimo.so"""
+testpy = "pixi run buildpy && pixi run python python/tests/test_decimo.py"
+tpy = "clear && pixi run testpy"


testpy runs pixi run pybuild, but there is no pybuild task—this file defines buildpy (and bpy as an alias). This will break pixi run testpy; update testpy to call the correct build task name or add a pybuild alias for consistency with the docs.

Copilot

Pull request overview

Copilot reviewed 20 out of 22 changed files in this pull request and generated 7 comments.

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Copilot · 2026-03-02T19:31:38Z

python/decimo_module.mojo

+    out self: BigDecimal, args: PythonObject, kwargs: PythonObject
+) raises:
+    """Construct a BigDecimal from a single argument (string, int, or float).


bigdecimal_py_init accepts kwargs but never checks/uses it. Calling _decimo.BigDecimal(value="1.23") will produce a misleading positional-args error rather than a clear "no keyword arguments" / keyword support. Either explicitly reject non-empty kwargs with a Python-like error, or implement keyword handling (e.g., value).

Copilot · 2026-03-02T19:31:38Z

python/decimo_module.mojo

+            "Decimal() takes exactly 1 argument ("
+            + String(len(args))
+            + " given)"
+        )
+    # Convert any Python object to its string representation, then construct.


The raised constructor error says Decimal() even though this is the _decimo.BigDecimal type. This will be confusing for users calling the extension type directly and for debugging. Adjust the message to reference BigDecimal() (or _decimo.BigDecimal()) to match the actual callable.

Copilot · 2026-03-02T19:31:38Z

python/decimo_module.mojo

+
+    Usage from Python:
+        Decimal("3.14")
+        Decimal(42)
+        Decimal(3.14)   # via str() conversion
+    """
+    if len(args) != 1:


This docstring claims the constructor accepts int/float, but the Python wrapper always passes str(value) and the binding currently just does String(args[0]). If non-string Python objects aren’t actually supported here, update the docstring to avoid promising behavior that callers of _decimo.BigDecimal won’t get.

Copilot · 2026-03-02T19:31:38Z

LICENSE

      identification within third-party archives.

-   Copyright [yyyy] [name of copyright owner]
+   Copyright 2026 Yuhao Zhu


This is part of the Apache-2.0 license appendix template (“How to apply…”). Editing the template text (e.g., replacing the bracketed copyright line) makes the LICENSE file diverge from the standard license text and can create ambiguity for downstream tooling. Keep the LICENSE text verbatim and put the project’s actual copyright notice in a NOTICE file and/or in source file headers.

Suggested change

Copyright 2026 Yuhao Zhu

Copyright [yyyy] [name of copyright owner]

Copilot · 2026-03-02T19:31:39Z

docs/plans/mojo4py.md

+```toml
+# python bindings (mojo4py)
+pybuild = "pixi run mojo build python/decimo_module.mojo --emit shared-lib -I src -o python/_decimo.so"
+pytest = "pixi run pybuild && pixi run python python/tests/test_decimo.py"
+```
+
+- `pixi run pybuild` — compiles the Mojo binding to `python/_decimo.so`.
+- `pixi run pytest` — builds then runs the Python test suite.


This plan doc references pixi run pybuild / pixi run pytest, but the actual tasks in pixi.toml are buildpy / testpy (and aliases bpy / tpy). Update the documentation snippet and quick-start commands to match the current task names so readers can follow it without errors.

Copilot · 2026-03-02T19:31:39Z

docs/plans/mojo4py.md

+pixi run pybuild    # Compiles python/decimo_module.mojo → python/_decimo.so
+pixi run pytest     # Builds, then runs python/tests/test_decimo.py


Quick-start uses pixi run pybuild / pixi run pytest, but those tasks don’t exist in the current pixi.toml (it defines buildpy / testpy). Adjust these commands to the real task names to keep the quick-start copy/pasteable.

Suggested change

pixi run pybuild # Compiles python/decimo_module.mojo → python/_decimo.so

pixi run pytest # Builds, then runs python/tests/test_decimo.py

pixi run buildpy # Compiles python/decimo_module.mojo → python/_decimo.so

pixi run testpy # Builds, then runs python/tests/test_decimo.py

Copilot · 2026-03-02T19:31:39Z

python/decimo_module.mojo

+from python import PythonObject
+from python.bindings import PythonModuleBuilder
+from os import abort
+
+from decimo import BigDecimal


Unused imports: Python and UnsafePointer are imported but not referenced in this module. Removing them avoids lint noise and keeps the binding module minimal.

…thon via `_decimo.so` (#179) Adds an initial “use mojo in python” proof-of-concept that exposes Decimo’s `BigDecimal` to Python via a Mojo-built CPython extension module (`_decimo.so`), with a thin Python wrapper (`decimo.Decimal`) providing Pythonic dunder/operator behavior. The PR also reorganizes shell test runners, integrates Python formatting (ruff) into tooling, and expands CI into parallel jobs. **Changes:** - Introduces `python/decimo_module.mojo` (`_decimo` extension), `python/decimo.py` (Python wrapper), and Python-side tests/stubs. - Refactors `tests/test_all.sh` into smaller test runners and adds a top-level `tests/test_decimo.sh` aggregator. - Updates `pixi.toml`, pre-commit, and GitHub Actions workflow to incorporate the new Python flow and formatting.

forfudan added 3 commits March 2, 2026 17:03

Prepare for mojo library in python

5f02c04

Update the folder name and structure

319a327

Update tests

6e22769

forfudan requested a review from Copilot March 2, 2026 19:12

Copilot started reviewing on behalf of forfudan March 2, 2026 19:13 View session

forfudan added 2 commits March 2, 2026 20:14

Fix bugs

3ec95ac

Fix bug

72b2a07

Copilot AI reviewed Mar 2, 2026

View reviewed changes

forfudan requested a review from Copilot March 2, 2026 19:21

Copilot started reviewing on behalf of forfudan March 2, 2026 19:22 View session

forfudan changed the title ~~[python] Implement basic Mojo-Python interop to import decimo in py files~~ [python] Implement basic use-mojo-in-python that exposes decimo to Python via _decimo.so Mar 2, 2026

Fix bugs

1104fc1

Copilot AI reviewed Mar 2, 2026

View reviewed changes

forfudan merged commit af8fc72 into cli Mar 2, 2026
9 checks passed

forfudan deleted the update branch March 2, 2026 19:34

-        return not self.__eq__(other)
+        eq_result = self.__eq__(other)
+        if eq_result is NotImplemented:
+            return NotImplemented
+        return not eq_result

	tcli = "clear && pixi run clitest"
	tcli = "clear && pixi run testcli"

	Copyright 2026 Yuhao Zhu
	Copyright [yyyy] [name of copyright owner]

		pixi run pybuild # Compiles python/decimo_module.mojo → python/_decimo.so
		pixi run pytest # Builds, then runs python/tests/test_decimo.py

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forfudan commented Mar 2, 2026 •

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