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Data structures · easy

13. Fixed-size arrays

Statically sized arrays with compile-time bounds.

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Vyper arrays have a fixed size baked into their type, e.g. `uint256[5]`. This is a key difference from Solidity, where dynamic arrays are common; Vyper favours fixed sizes because they make gas costs and memory layout fully predictable.

scores: public(uint256[5])

@external
def set_score(i: uint256, value: uint256):
    assert i < 5, "out of bounds"
    self.scores[i] = value

Out-of-bounds indexing reverts automatically — you don't need to write your own bounds check, though doing so gives a clearer revert message.

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Check your understanding

  1. 1. How is a fixed-size array of 5 uint256 declared?

  2. 2. What happens when you index out of bounds?

  3. 3. Why does Vyper favour fixed-size arrays?

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