Environment Variables and Constants ###################################

.. _types-env-vars:

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 bytes32 Current randomness beacon provided by the beacon chain block.number uint256 Current block number block.gaslimit uint256 Current block's gas limit block.basefee uint256 Current block's base fee block.blobbasefee uint256 Current block's blob gas base fee 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.mana uint256 Remaining gas (alias for msg.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 the ``block.difficulty`` opcode. Since ``block.difficulty`` is considered deprecated according to `EIP-4399 <https://eips.ethereum.org/EIPS/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>`.

.. _constants-self:

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 internal 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:

.. code-block:: vyper

    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:

.. code-block:: vyper

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

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

.. _types-constants:

Custom Constants

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

.. code-block:: vyper

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

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