How to Write Smart Contracts on Tezos Using SmartPy

The Tezos blockchain distinguishes itself with a focus on formal verification and upgradability, attracting developers interested in building secure, long-lasting decentralized applications (dApps). While the native, stack-based language for writing smart contracts on Tezos is Michelson, it is considered low-level and complex for direct use. To bridge this gap, high-level languages like SmartPy and Ligo have emerged. These languages, particularly SmartPy, allow developers to write more intuitive code that is ultimately compiled down to Michelson for execution on the Tezos blockchain. This layered approach combines developer-friendly syntax with the security and formal verification capabilities inherent to Tezos’s design.

SmartPy’s primary advantage is its foundation in Python, one of the world’s most popular and accessible programming languages. This significantly lowers the barrier to entry for blockchain development. Developers with Python experience can quickly adapt, while newcomers can leverage Python’s vast learning resources. The platform provides an Integrated Development Environment (IDE) that streamlines writing, testing, and compiling contracts, making the entire development lifecycle more efficient. By abstracting the complexities of Michelson, SmartPy empowers a broader range of developers to contribute to the Tezos ecosystem, directly supporting the network’s growth and the value proposition of its native token, XTZ.

Building a smart contract in SmartPy begins with defining its storage, which acts as the contract’s persistent database on the blockchain. In the provided tutorial example, a contract is created to manage user data. The contract is defined as a Python class inheriting from `sp.Contract`. The storage is initialized within the class constructor using `self.init()`. For the user management contract, the storage is a map—a key-value data structure—where a user’s email serves as the key, and a record containing their name, gender, and score is the value. This structure, `self.init(userMap = sp.map())`, establishes the foundational state that the contract will manage and modify.

The logic of the contract is exposed through entry points, which are functions that external calls can invoke to interact with the contract’s storage. These are marked with the `@sp.entry_point` decorator. The tutorial contract features two entry points. The `addUser` entry point takes parameters (email, name, gender) and creates a new record in the `userMap` with an initial score of zero. The `updateScore` entry point takes an email and a score value, then adds that value to the existing score of the corresponding user. Crucially, the contract’s storage is accessed and modified via `self.data`, ensuring all state changes are recorded immutably on the Tezos blockchain. This demonstrates how smart contracts enable decentralized applications by managing state and logic in a transparent, trustless environment.

Before a smart contract is deployed to the Tezos testnet or mainnet, rigorous testing is essential. Given the immutable and often financial nature of blockchain applications, bugs can be catastrophic. SmartPy integrates a robust testing framework directly into its workflow. Developers write tests by creating a test scenario using `sp.test_scenario()`, which simulates the blockchain environment. In the tutorial, a test is defined to verify both entry points: first adding a user ‘Bob’ with an email and gender, and then updating his score by 10.

The scenario object visually displays the state of the contract at each step, showing the initial empty storage, the state after the user is added, and the final state after the score update. This process validates that the contract’s logic behaves as intended and that storage updates correctly. Running these tests within the SmartPy IDE provides immediate feedback, allowing developers to iterate quickly. This emphasis on pre-deployment testing aligns with the broader Tezos philosophy of security and formal verification, ensuring that only well-vetted code reaches the blockchain. Mastering this step is critical for any developer aiming to build reliable, production-ready dApps on Tezos using the SmartPy platform.