Environment Variables and Constants

Environment Variables

Environment variables always exist in the namespace and are primarily used to provide information about the blockchain or current transaction.

Block and Transaction Properties

Name

Type

Value

block.coinbase

address

Current block miner’s address

block.difficulty

uint256

Current block difficulty

block.prevrandao

uint256

Current randomness beacon provided by the beacon chain

block.number

uint256

Current block number

block.prevhash

bytes32

Equivalent to blockhash(block.number - 1)

block.timestamp

uint256

Current block epoch timestamp

chain.id

uint256

Chain ID

msg.data

Bytes

Message data

msg.gas

uint256

Remaining gas

msg.sender

address

Sender of the message (current call)

msg.value

uint256

Number of wei sent with the message

tx.origin

address

Sender of the transaction (full call chain)

tx.gasprice

uint256

Gas price of current transaction in wei

Note

block.prevrandao is an alias for block.difficulty. Since block.difficulty is considered deprecated according to EIP-4399 after “The Merge” (Paris hard fork), we recommend using block.prevrandao.

Note

msg.data requires the usage of slice to explicitly extract a section of calldata. If the extracted section exceeds the bounds of calldata, this will throw. You can check the size of msg.data using len.

The self Variable

self is an environment variable used to reference a contract from within itself. Along with the normal address members, self allows you to read and write to state variables and to call private functions within the contract.

Name

Type

Value

self

address

Current contract’s address

self.balance

uint256

Current contract’s balance

Accessing State Variables

self is used to access a contract’s state variables, as shown in the following example:

state_var: uint256

@external
def set_var(value: uint256) -> bool:
    self.state_var = value
    return True

@external
@view
def get_var() -> uint256:
    return self.state_var

Calling Internal Functions

self is also used to call internal functions within a contract:

@internal
def _times_two(amount: uint256) -> uint256:
    return amount * 2

@external
def calculate(amount: uint256) -> uint256:
    return self._times_two(amount)

Custom Constants

Custom constants can be defined at a global level in Vyper. To define a constant, make use of the constant keyword.

TOTAL_SUPPLY: constant(uint256) = 10000000
total_supply: public(uint256)

@external
def __init__():
    self.total_supply = TOTAL_SUPPLY