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constants-and-vars.rst

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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 :func:`slice <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 :func:`len <len>`.

The self Variable

self is an environment variable used to reference a contract from within itself. Along with the normal :ref:`address<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 :ref:`state variables<structure-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 :ref:`internal functions<structure-functions-internal>` 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