A contract can have a default function, executed when a function that does not exist is called. This is the same function as the fallback function in Solidity.
This function is named __default__ and it is commonly used to receive Ether.
# pragma version ^0.4.0
event Payment:
sender: indexed(address)
amount: uint256
@external
@payable
def __default__():
log Payment(msg.sender, msg.value)
