Vyper Smart Contract Compiler

0.4.3 · active · verified Thu Apr 16

Vyper is a Pythonic programming language for the Ethereum Virtual Machine (EVM), designed with security, auditability, and simplicity in mind. It provides a more constrained set of features compared to other EVM languages, aiming to reduce complexity and potential vulnerabilities. The current version is 0.4.3, with minor releases and release candidates occurring frequently, typically leading to stable minor versions every few months.

Common errors

```
ModuleNotFoundError: No module named 'vyper'
```
cause The Vyper library has not been installed in the current Python environment.

fix Run `pip install vyper` to install the library.
```
SyntaxException: line X:X 'some_invalid_keyword' is not allowed
```
cause There is a syntax error or an attempt to use a non-existent keyword or feature in your Vyper contract code.

fix Review the Vyper contract code against the official Vyper documentation for the specific version you are using. Vyper has a minimalist design, so many Solidity features are not present.
```
ValueError: Vyper does not support python version 3.9.x (or similar for other unsupported versions)
```
cause You are attempting to run Vyper with an unsupported Python version. Vyper typically requires Python 3.10+ but less than 4.

fix Switch your Python environment to a compatible version (e.g., 3.10, 3.11, 3.12). You can use `pyenv install 3.12.0 && pyenv local 3.12.0` or create a new virtual environment with the correct Python version.
```
KeyError: 'bytecode' (or 'abi') when accessing compiled_artifacts
```
cause The specified `output_formats` in `compile_code` did not include the key you are trying to access, or compilation failed silently without producing all artifacts.

fix Ensure that the `output_formats` list explicitly includes all the keys you intend to access (e.g., `['bytecode', 'abi', 'ast_dict']`). Check for compilation errors if outputs are still missing.

Warnings

breaking Vyper adheres to a `0.x.x` versioning scheme, meaning breaking changes can occur in minor releases. Always review release notes when upgrading between `0.X.x` versions (e.g., from 0.3.x to 0.4.x).
Fix: Consult the official Vyper release notes (docs.vyperlang.org/en/latest/release-notes.html) for specific upgrade instructions and breaking changes.
breaking The default EVM version targeted by the compiler can change in minor releases (e.g., to 'prague' in v0.4.3). This might affect bytecode generation and compatibility with specific chain deployments if not explicitly handled.
Fix: Always explicitly specify the target EVM version using the `evm_version` parameter in `compile_code` or the `--evm-version` CLI flag to ensure consistent bytecode across environments.
gotcha Vyper requires Python 3.10 or higher, but strictly less than Python 4.0. Running with an unsupported Python version will lead to installation or runtime errors.
Fix: Ensure your environment uses a compatible Python version (e.g., `python3.10` or `python3.11`). Use `pyenv` or `conda` for managing Python versions if necessary.
breaking Recent releases (e.g., v0.4.1) have included security-related fixes for low-to-moderate severity vulnerabilities. Older versions may contain known security flaws.
Fix: Always use the latest stable version of Vyper to benefit from critical security patches. Regularly check the official Vyper GitHub for security advisories.
gotcha Experimental compiler features, such as the `--venom` or `--experimental-codegen` flags (aliases), are subject to rapid change, may contain bugs, or produce unoptimized/unexpected bytecode. They are not recommended for production deployments.
Fix: Avoid using experimental features in production. If used for development, be aware of potential instabilities and thoroughly test generated bytecode.

Install

pip install vyper Install Vyper

Imports

compile_code
wrong:
```
import vyper.compiler
```
correct:
```
from vyper import compile_code
```
The primary programmatic compilation function `compile_code` is directly available from the top-level package.

Quickstart

This quickstart demonstrates how to programmatically compile a basic Vyper smart contract using the `compile_code` function. It specifies the desired output formats (bytecode and ABI) and an EVM version for compilation, then prints the resulting artifacts.

from vyper import compile_code

contract_code = '''
# @version ^0.4.0

# A simple Vyper contract

@external
def hello() -> String[100]:
    return "Hello, Vyper!"
'''

# Compile the contract to get bytecode, ABI, and other artifacts
compiled_artifacts = compile_code(
    contract_code,
    output_formats=['bytecode', 'abi'],
    evm_version='shanghai' # Specify EVM version for compatibility
)

print("Bytecode:", compiled_artifacts['bytecode'])
print("ABI:", compiled_artifacts['abi'])

view raw JSON →