.. image:: logo.svg :width: 140px :alt: Vyper logo :align: center

Vyper

Vyper is a Pythonic smart contract language that compiles to Ethereum Virtual Machine (EVM) <https://ethereum.org/learn/#ethereum-basics>_ bytecode. It prioritises security, auditability, and simplicity.

.. _design-principles:

Principles

• Security: Building secure smart contracts should be natural, not an uphill battle.
• Simplicity: Both the language and compiler should be easy to understand.
• Auditability: Code should be maximally human-readable. Simplicity for the reader matters more than convenience for the writer.

Key Features

Safety by default

• Bounds and overflow checking on array accesses and arithmetic
• Reentrancy protection via the @nonreentrant decorator (see :ref:control-structures)
• Strong typing with explicit :ref:type conversions <type_conversions>

Predictable execution

• Decidable gas consumption: every function call has a calculable upper bound
• Bounded loops only (compile-time maximum iterations)
• No recursion: execution flow is structurally decreasing

Clean code reuse

• :ref:Module imports <modules> instead of class inheritance
• Explicit extcall and staticcall keywords for external contract interactions
• Support for :ref:pure functions <function-mutability> that cannot modify state

Compiler-Enforced Security

Vyper eliminates entire vulnerability classes by excluding features that enable dangerous patterns:

.. list-table:: :header-rows: 1 :widths: 25 75

• • Excluded Feature
  • Why It Matters
• • Inline assembly
  • Preserves type safety, overflow protection, and searchability of variable usage
• • Class inheritance
  • Removes ambiguity about which code executes and simplifies auditing
• • Modifiers
  • All checks are inline and visible, no hidden pre/post conditions
• • Function overloading
  • Function calls are unambiguous; foo(x) always means the same thing
• • Operator overloading
  • Arithmetic operators do exactly what they appear to do
• • Infinite loops
  • Gas costs are always bounded and predictable
• • Recursive calls
  • Call graphs are simple and gas limits are enforceable

These constraints mean developers cannot accidentally introduce dangerous patterns, even under time pressure or with limited blockchain experience.

Decimal Fixed Point

Vyper uses decimal (not binary) fixed point numbers. This ensures that literals like 0.1 have exact representations, avoiding the subtle precision errors common in binary floating-point arithmetic.