Troubleshooting (Python)

How the native library is found

Mesmo(lib_path=None) resolves libmesmo.dylib / libmesmo.so / libmesmo.dll in this order:

1. The explicit lib_path constructor argument (a directory).
2. The MESMO_LIB_PATH environment variable (a directory) — the usual way to run against a locally built library.
3. A copy bundled inside the installed wheel (mesmo/_libs/) — this is what a normal pip install uses.
4. The bare filename, letting the OS loader search its default paths.

On Windows, the library’s directory is registered with os.add_dll_directory so sibling DLL dependencies resolve.

Common errors

OSError loading the library

The library file wasn’t found or couldn’t be loaded.

• Wheel install: make sure you installed a wheel built for your platform (check pip show -f cardano-client-lib lists mesmo/_libs/libmesmo...). A source install has no bundled library — set MESMO_LIB_PATH.
• Local build: set MESMO_LIB_PATH to the directory containing the library, and make the OS loader happy for its transitive dependencies:

  export MESMO_LIB_PATH=/path/to/core/build/native/nativeCompile
  export DYLD_LIBRARY_PATH=$MESMO_LIB_PATH   # macOS
  export LD_LIBRARY_PATH=$MESMO_LIB_PATH     # Linux

• Unsupported platform (macOS Intel): no prebuilt library exists — build from source (below).

RuntimeError: ... incompatible ... (version mismatch)

The wrapper and the native library must match on base semver. This appears when MESMO_LIB_PATH points at a stale build. Rebuild the library, or (at your own risk) set MESMO_SKIP_VERSION_CHECK=1.

MesmoClosedError

Something called the instance after close() (or after its with block ended). This exception is the wrapper saving you: handing a stale isolate handle to the native side would abort the whole interpreter. Keep calls inside the instance’s lifetime, or create a new Mesmo.

TypeError / ValueError about network

The network argument is required and validated — there is no default (a silent mainnet default was removed deliberately). Pass Network.MAINNET or Network.TESTNET.

Mesmo error -10: ... from quicktx.build

MESMO_ERROR_TX_BUILD — the TxPlan didn’t build. Usual causes:

• Malformed YAML or a wrong intent field name (check against the TxPlan reference).
• A Plutus transaction with wrong/missing execution units.
• Mesmo error -8 (INSUFFICIENT_FUNDS) means the supplied UTXOs can’t cover outputs + fee.

tx.from_json / plutus.data_to_json / plutus.data_from_json fail

Known limitation of the current native library (GraalVM reflection configuration gaps). Use the working alternatives: a managed account’s sign_tx for signing, plutus.data_hash for datum hashing.

Building the native library from source

Needed only on platforms without a prebuilt library (macOS Intel) or for development against Mesmo itself:

git clone https://github.com/bloxbean/mesmo
cd mesmo
sdk install java 25.0.3-graal        # GraalVM with native-image
./gradlew :core:nativeCompile        # → core/build/native/nativeCompile/libmesmo.*
export PYTHONPATH=$PWD/wrappers/python
export MESMO_LIB_PATH=$PWD/core/build/native/nativeCompile

Platform support

Platform	Prebuilt	Notes
Linux x86_64 (glibc ≥ 2.17)	✅	RHEL/CentOS 7+, Ubuntu 18.04+, Debian 9+, Amazon Linux 2, …
Linux aarch64 (glibc ≥ 2.17)	✅
macOS Apple Silicon	✅
macOS Intel	❌	Oracle GraalVM dropped Intel Macs
Windows x86_64	✅

Alpine/musl: the musl native library exists (the Go/Rust/JS wrappers use it), but musllinux wheel publishing is still being wired up — on Alpine, install from source with MESMO_LIB_PATH pointing at the musl libmesmo.so for now.