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.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)

Note

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.

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