MolGR

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MolGR stands for Moleculer Graph Reconstructor.

MolGR is a Python package for reconstructing molecular graphs from XYZ coordinates. It accepts an XYZ block, total charge, and spin multiplicity, and returns an rdkit.Chem.Mol with bond orders, a 3D conformer, optional dative bonds, and optional stereochemistry.

MolGR currently provides two switchable reconstruction backends:

• cpp: the default backend, exposed through molgr._core, for regular use and performance-sensitive workflows.
• python: the Python reference implementation in src/molgr/fallback/, used for semantic alignment, debugging, and regression tests.

Quick Usage

The main entrypoint is molgr.interface.xyz_to_rdmol:

from molgr.interface import xyz_to_rdmol

xyz = """3
water
O 0.000000 0.000000 0.000000
H 0.758602 0.000000 0.504284
H -0.758602 0.000000 0.504284
"""

mol = xyz_to_rdmol(
    xyz,
    total_charge=0,
    spin_multiplicity=1,
    backend="cpp",  # "python" is also available
)

Before reconstruction, MolGR calculates the total electron count as the sum of the atomic numbers minus total_charge and rejects impossible spin multiplicities. In particular, even-electron systems require odd multiplicities, while odd-electron systems require even multiplicities. The accepted spin_multiplicity is then normalized as total_radical_electrons = spin_multiplicity - 1. By default, MolGR also completes possible dative bonds and stereochemistry. Pass make_dative_bonds=False or make_stereochemistry=False to disable those post-processing steps.

Configuration

Runtime configuration is dataclass-based. The package-level molgr.config.CONFIG object is used by default, and callers may either mutate that global object or pass an explicit MolGRConfig to xyz_to_rdmol(..., config=...).

from molgr.config import CONFIG

CONFIG.cpp_backend.enable_target_bucket_parallelism = True
CONFIG.cpp_backend.target_bucket_parallel_threshold = 1
CONFIG.cpp_backend.target_bucket_parallel_max_threads = None

On Windows, CONFIG.cpp_backend.max_threads defaults to 1. Enabling C++ backend thread parallelism on Windows is not recommended: concurrent Open Babel reconstruction can cause native access violations that Python cannot catch. Keep max_threads=1 unless the complete workload has been validated locally. Linux and macOS keep the automatic None default.

The C++ backend is the default accelerated implementation of the Python fallback semantics. C++-only switches may change scheduling, caching, or thread-safe vendor implementations, but they must not change the selected molecule for the same MolGRConfig.

Installation

MolGR requires Python >=3.8. Runtime and build dependencies are declared in pyproject.toml. The default development workflow uses uv.

C++ Build Requirements

Building from source compiles the molgr._core extension. The local build environment must provide:

• CMake >=3.15.
• A C++17-capable compiler:
  • Linux: GCC 9+ or Clang 10+.
  • macOS: Apple Clang from a current Xcode Command Line Tools installation.
  • Windows: MSVC Build Tools 2019+ with the C++ workload.
• Python development headers for the active Python interpreter. In virtual environments created by uv, this is usually provided by the selected Python installation.
• Python build packages from pyproject.toml: scikit-build-core, pybind11, setuptools-scm, and openbabel-wheel.
• A working OpenBabel wheel for the target platform. The CMake build locates OpenBabel headers and libraries from the installed openbabel-wheel package.

Install from source and build the C++ extension:

cd MolGR
uv sync --dev
uv pip install -e . -v --no-build-isolation

Editable installation builds the C++ extension through scikit-build-core, pybind11, and the OpenBabel package available in the current Python environment. After changing C++ code or pybind11 bindings, rebuild before running affected tests:

make cpp-build

To mimic CI-style dependency resolution against PyPI instead of the local mirror configured in pyproject.toml, pass explicit indexes:

uv sync --dev --index https://pypi.org/simple --default-index https://pypi.org/simple
uv pip install -e . -v --no-build-isolation \
  --index https://pypi.org/simple \
  --default-index https://pypi.org/simple

Project Layout

• src/molgr/interface.py: public API, config resolution, backend routing, and RDKit post-processing.
• src/molgr/fallback/: Python reference implementation.
• src/cpp/: C++ reconstruction implementation.
• src/bindings/: pybind11 bindings for molgr._core.
• src/molgr/utils/: conversion, equivalence, and RDKit post-processing utilities.
• tests/: public behavior tests, fallback tests, converter tests, and C++ parity tests.
• benchmarks/: benchmark entrypoints, dedicated dependencies, and benchmark docs.
• docs/: architecture and release documentation.
• docs/development/MOLECULE_REVIEW_TOOL.md: MolGR reconstruction review and trace tool.

Algorithm Overview

MolGR treats the Python fallback as the semantic reference and the C++ backend as the accelerated path. Both backends follow the same high-level reconstruction flow:

1. Parse the XYZ input and determine reconstruction targets from total charge, spin multiplicity, and runtime config.
2. Route to backend="cpp" or backend="python".
3. For metal-free structures, search neighboring-radical seeds in increasing charge-separation discrepancy layers. The layers share resonance deduplication state and stop at the first valid layer; deformed-pi and bond-break recovery run only if every primary layer is empty.
4. For metal-containing structures, temporarily strip metals from the organic core, enumerate possible metal states, and group those states by the induced organic charge/radical target.
5. Reconstruct each organic target bucket once, then reuse it across corresponding metal candidates.
6. Score organic candidates or combined metal-organic candidates and select the best state.
7. Convert backend output to an RDKit molecule and optionally complete dative bonds and stereochemistry.

See docs/architecture/ALGORITHM_ARCHITECTURE.md for the full call graph, metal search, resonance recovery, and C++ optimization notes.

Development

Create or refresh the development environment:

uv sync --dev

Build the extension in editable mode:

uv pip install -e . -v --no-build-isolation

Common checks:

uv run ruff check .
uv run ruff format --check .
uv run mypy src
uv run pyright
uv run pytest

Build source and wheel distributions:

uv build

The root makefile provides common development shortcuts:

• make format: run the Ruff formatter; modifies files.
• make lint: run ruff check . --fix; modifies files.
• make test: run pytest.
• make type-check: run MyPy and Pyright on src.
• make cpp-build: rebuild the editable C++ extension and refresh C++ IDE config.
• make stubs: regenerate type stubs for the compiled extension.

make stubs runs pybind11-stubgen against molgr._core, keeps the public pipeline stubs and the development/parity helper stubs under src/molgr/_core/dev/, then formats and lints the generated .pyi files.

Optional VSCode/clangd C++ configuration:

uv run python scripts/gen_vscode_config_with_ob.py --build-dir build

Testing

Run the full test suite:

uv run pytest

Useful focused tests during development:

uv run pytest tests/test_main.py
uv run pytest tests/test_backend_reconstruction_regression.py
uv run pytest tests/test_fallback_resonance.py
uv run pytest tests/test_fallback_get_possible_metal_radicals.py

When changing C++, pybind11 bindings, or the _core public surface:

1. Rebuild the extension with make cpp-build.
2. Run affected C++/Python parity tests, for example tests/test_backend_reconstruction_regression.py tests/test_cpp_python_metal_candidate_parity.py, tests/test_cpp_uff_atom_typing_cache.py, and tests/test_force_field_scoring_policy.py.
3. If binding interfaces changed, run make stubs and inspect the generated .pyi files.

The C++ backend is an acceleration of the Python fallback semantics. Keep the backend parity guardrails in docs/architecture/ALGORITHM_ARCHITECTURE.md in sync when changing SMARTS matching, UFF setup state, resonance selection, or C++-only acceleration switches.

Some tests depend on OpenBabel. They may be skipped when the dependency is unavailable.

Benchmark

Benchmark dependencies live in benchmarks/pyproject.toml, separate from the release dependency graph and the root uv.lock. Benchmarks use a dedicated environment: default path .venv-benchmark, default Python executable python3.10.

Create or refresh the benchmark environment:

bash scripts/benchmark_env.sh create

Run the SMILES/XYZ benchmark:

bash scripts/benchmark_env.sh run python benchmarks/smiles_xyz_benchmark/run.py \
  --input tests/test_cases.csv \
  --limit 10 \
  --out benchmarks/_runs/smiles-demo

Run the Molfile/SDF benchmark:

bash scripts/benchmark_env.sh run python benchmarks/molfile_xyz_benchmark/run.py \
  --input tests/data/sdf/MoNNMo.sdf \
  --limit 1 \
  --out benchmarks/_runs/molfile-demo

Run a tmQMg backend parity subset:

bash scripts/benchmark_env.sh run python benchmarks/tmqmg_xyz_benchmark/run.py \
  --csv /path/to/tmqmg.csv \
  --xyz-dir /path/to/xyz \
  --limit 1000 \
  --out benchmarks/_runs/tmqmg-parity \
  --case-timeout-seconds 1.0 \
  --cpp-accelerations all \
  --methods molgr_cpp,molgr_fallback

For repeated benchmark commands, switch the current shell environment:

eval "$(bash scripts/benchmark_env.sh env)"

Restore the default project environment:

unset UV_PROJECT UV_PROJECT_ENVIRONMENT UV_PYTHON

See benchmarks/README.md or benchmarks/README.zh-CN.md for details.

Documentation

• docs/README.md: English documentation index.
• docs/README.zh-CN.md: Chinese documentation index.
• docs/architecture/ALGORITHM_ARCHITECTURE.md: English algorithm architecture.
• docs/architecture/ALGORITHM_ARCHITECTURE.zh-CN.md: Chinese algorithm architecture.
• docs/release/DEVELOPMENT_RELEASE_GUIDE.md: English development and release guide.
• docs/release/DEVELOPMENT_RELEASE_GUIDE.zh-CN.md: Chinese development and release guide.
• benchmarks/README.md: English benchmark environment, commands, and outputs.
• benchmarks/README.zh-CN.md: Chinese benchmark environment, commands, and outputs.

License

MolGR is released under the GNU General Public License v2. See LICENSE.