Functions

Functions are executable units of code defined in a contract. It can be accessed internally or externally depending on their visibility.

Vyper has two unique function declaration:

__init__: Constructor function which is only invoked during contract deployment.
__default__: Fallback function to handle undefined calls within a contract.

# pragma version 0.4.0

example_integer: public(uint256)
example_string: public(String[100])

# Example of constructor function from Mutability lesson
@deploy
@payable
def __init__():
    self.example_integer = 534532

# Function example which modifies state
@external
def updateString(new_string: String[100]):
    self.example_string = new_string

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

# Example of getter function
@external
@view
def getExampleInteger() -> uint256:
    return self.example_integer

__default__ function

event FallbackEventLog:
    amount: uint256
    sender: indexed(address)

# Default (fallback) function must always be annotated with `@external`
# If the function has `@payable` decorator, it will be triggered when the contract receives Ether without data
@external
@payable
def __default__():
    log FallbackEventLog(msg.value, msg.sender)

Vyper Differentiators

The __default__() function cannot accept arguments.

Vyper offers a collection of built-in functions used for bitwise operations, chain interactions, and many more which are worth exploring. Refer to the further reading section below for more details.

Functions

Further Reading: