A Guide to Writing Your First Smart Contract in Vyper

Understanding Vyper's Design Philosophy

1. Vyper prioritizes security and auditability over feature richness, deliberately omitting complex constructs like inheritance and recursive calls.

2. The language enforces explicit visibility declarations for all functions and state variables, reducing ambiguity during contract review.

3. It uses Python-like syntax but compiles directly to EVM bytecode without intermediate abstractions, minimizing attack surface.

4. Integer overflow and underflow protection is built-in—no manual SafeMath patterns required.

5. All external calls are marked with the @external decorator, making interaction boundaries immediately visible in source code.

Setting Up the Development Environment

1. Install Python 3.9+ and pip, then run pip install vyper to get the official compiler.

2. Use VS Code with the Vyper extension for syntax highlighting and basic linting support.

3. Configure a local testnet node via Anvil or use Foundry’s anvil command to simulate Ethereum execution.

4. Integrate with pytest for unit testing—Vyper contracts expose ABI-compatible interfaces that pytest can invoke directly.

5. Store compiled bytecode and ABI in separate JSON files after running vyper -f json my_contract.vy.

Writing a Minimal Token Contract

1. Declare storage variables using public or private modifiers, such as balance_of: public(HashMap[address, uint256]).

2. Define the constructor with @external and initialize total supply and owner balance in one atomic block.

3. Implement transfer logic with strict checks: sender balance sufficiency, non-zero recipient address, and event emission using log Transfer(...).

4. Use assert statements instead of revert strings to enforce invariants—Vyper does not support custom error messages.

5. Avoid loops with unbounded iteration; fixed-length arrays and bounded for-loops only are permitted to prevent gas exhaustion.

Compiling and Deploying on Testnet

1. Compile with vyper -f combined_json my_contract.vy to generate both bytecode and ABI in one output.

2. Use web3.py to connect to an RPC endpoint, instantiate a contract object, and sign deployment transactions with a private key.

3. Verify gas estimation before submission—Vyper’s deterministic compilation allows accurate pre-deployment gas cost prediction.

4. Confirm deployment by querying the contract address on Etherscan testnet explorer and checking emitted events.

5. Interact via web3.eth.contract() methods, ensuring all arguments match expected types defined in the Vyper source.

Frequently Asked Questions

Q: Does Vyper support floating-point arithmetic?A: No. Vyper does not include native floating-point types. Fixed-point math must be implemented manually using integer scaling factors.

Q: Can I call another Vyper contract from within my contract?A: Yes, but only if the target contract’s interface is explicitly declared using interface blocks and the call is made through a typed variable.

Q: How are structs handled in Vyper?A: Structs are supported as named groupings of fields, but they cannot be nested or used as mapping keys. They must be declared globally with the struct keyword.

Q: Is there a standard way to handle time-based logic in Vyper?A: Yes. Use block.timestamp directly—it is accessible as a global constant and behaves identically to Solidity’s version.