Interface

Interface defines all of the contract's externally available functions. It enables calls between contracts.

Important to specify the interface with mutability decorator. This indicates whether the call will modify the state or not.

extcall keyword shall be used for payable and nonpayable functions.
staticcall keyword shall be used for pure and view functions.

You can create interface to interact with other contract using interface keyword.

Reference.vy:

# pragma version 0.4.0

example_integer: public(uint256)

@external
def set_example_integer(x: uint256):
    self.example_integer = x

@external
@view
def get_example_integer() -> uint256:
    return self.example_integer

InterfaceExample.vy:

# pragma version 0.4.0

interface ExampleInterface:
    def example_integer() -> uint256: view
    def set_example_interface(x: uint256): nonpayable
    def get_example_integer() -> uint256: view

# state variable to reference `Reference.vy`
interface_reference: public(ExampleInterface)

interface_variable: public(uint256)

@deploy
def __init__(reference_addr: address):
    self.interface_reference = ExampleInterface(reference_addr)

# pass the `Reference.vy` deployed contract address to test out function below
@external
def setInterfaceVariable(x: uint256):

    # declare `extcall` keyword for functions which modifies state
    extcall self.interface_reference.set_example_interface(x)

@external
@view
def getInterfaceVariable() -> uint256:

    # declare `staticcall` keyword for functions which does not modify state
    return staticcall self.interface_reference.get_example_integer()

Vyper Differentiators

Vyper has built-in interfaces such as IERC20 and IERC721.

You can also import interface via a separate .vyi file.

Interface

Further Reading: