2. Version pragma and file layout

Every Vyper file should declare the compiler version it was written for using a comment pragma. This isn't optional style — the compiler refuses to build if the installed version falls outside the stated range.

A typical file layout is: version pragma, imports/interfaces, state variables, events, constructor, then external and internal functions grouped by purpose.

# @version ^0.3.10

from vyper.interfaces import ERC20

owner: public(address)
token: public(address)

event Deposited:
    amount: uint256

Unlike Solidity's `pragma solidity`, Vyper's version comment must start with `# @version` and is checked strictly against the installed compiler.

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