Mutability

In addition to visibility decorators, Vyper have four types of optional decorators which can be used to declare a function's mutability.

@pure: purely to execute a function without reading or modifying state.
@view: to read state but not modify it. Necessary decorator to define getter functions.
@nonpayable(default): prevents receival of Ether.
@payable: can receive and access Ether via msg.value.

# pragma version 0.4.0

example_integer: public(uint256)

# If the decorator "@payable" is absent, the contract will not be able to receive Ether
@deploy
@payable
def __init__():
    self.example_integer = 534532

# Pure function to test addition function without modifying state
@external
@pure
def purelyAddingFunction(x: uint256, y: uint256) -> uint256:
    return x + y

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

Vyper Differentiators

Initiate the contract with @payable to allow contract to hold Ether.

Mutability

Further Reading: