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.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

msg.data, msg.sender and msg.value can only be accessed from external functions. If you require these values within a private function, they must be passed as parameters.

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)

Built In Constants

Vyper has a few convenience constants builtin.

Name

Type

Value

ZERO_ADDRESS

address

0x0000000000000000000000000000000000000000

EMPTY_BYTES32

bytes32

0x0000000000000000000000000000000000000000000000000000000000000000

MAX_INT128

int128

2**127 - 1

MIN_INT128

int128

-2**127

MAX_DECIMAL

decimal

(2**127 - 1)

MIN_DECIMAL

decimal

(-2**127)

MAX_UINT256

uint256

2**256 - 1

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