Structure of a Contract¶
Vyper contracts are contained within files. Each file contains exactly one contract.
This section provides a quick overview of the types of data present within a contract, with links to other sections where you can obtain more details.
Version Pragma¶
Vyper supports a version pragma to ensure that a contract is only compiled by the intended compiler version, or range of versions. Version strings use NPM style syntax.
# @version ^0.2.0
In the above example, the contract only compiles with Vyper versions 0.2.x.
State Variables¶
State variables are values which are permanently stored in contract storage. They are declared outside of the body of any functions, and initially contain the default value for their type.
storedData: int128
State variables are accessed via the self object.
self.storedData = 123
See the documentation on Types or Scoping and Declarations for more information.
Functions¶
Functions are executable units of code within a contract.
@external
def bid():
...
Functions may be called internally or externally depending on their visibility. Functions may accept input arguments and return variables in order to pass values between them.
See the Functions documentation for more information.
Events¶
Events provide an interface for the EVM’s logging facilities. Events may be logged with specially indexed data structures that allow clients, including light clients, to efficiently search for them.
event Payment:
amount: int128
sender: indexed(address)
total_paid: int128
@external
@payable
def pay():
self.total_paid += msg.value
log Payment(msg.value, msg.sender)
See the Event documentation for more information.
Interfaces¶
An interface is a set of function definitions used to enable calls between smart contracts. A contract interface defines all of that contract’s externally available functions. By importing the interface, your contract now knows how to call these functions in other contracts.
Interfaces can be added to contracts either through inline definition, or by importing them from a separate file.
interface FooBar:
def calculate() -> uint256: view
def test1(): nonpayable
from foo import FooBar
Once defined, an interface can then be used to make external calls to a given address:
@external
def test(some_address: address):
FooBar(some_address).calculate()
See the Interfaces documentation for more information.