LLL Support

Populus provides partial support for LLL, in particular the lllc compiler, currently maintained in tandem with Solidity, in the ethereum/solidity repository.

Known limitations

This feature is highly experimental; mixing different languages, e.g. Solidity and LLL or Viper and LLL, is not yet possible.

Since LLL is very low-level, not all language constructs are currently supported. In particular, string literals, especially defined with the lit keyword, may be impossible to use.

Finally, LLL programs have no notion of web3 ABI, as detailed in the Ethereum Contract ABI specification. For that reason, all .lll files must have an accompanying .lll.abi file, specifying in JSON the on-chain contract’s interface.


On Ubuntu-based systems, lllc should be available in the same package as solc.

In general, lllc should be available in PATH; or an LLLC_BINARY environment variable must be set and pointing to the lllc executable.

To see if it’s present:

$ lllc --version
LLLC, the Lovely Little Language Compiler
Version: 0.4.19-develop.2017.12.1+commit.c4cbbb05.Linux.g++


Automatic initialisation of a Greeter project in LLL with populus --init is not yet possible.

This section describes how to do it manually.

Change compilation backend

The compilation backend must be changed from its default in project.json by placing a backend key in the compilation section, as shown below:

    "version": "7",
    "compilation": {
        "contracts_source_dirs": ["./contracts"],
        "import_remappings": [],
        "backend": {
            "class": "populus.compilation.backends.LLLBackend"

Populus will now only compile LLL contracts in the configured contracts directories.

Copy LLL-specific Greeter contract and its ABI specification

These files should be available in the Populus repository, as Greeter.lll and Greeter.lll.abi.

Place them in the contracts directory of your project.

Copy LLL-specific test

This file should be available in the Populus repository, as test_greeter_lll.py.

Place it in the tests directory of your project.

Remove the Solidity/Viper test_greeter.py if it’s still present, so pytest doesn’t trip.