The ScriptContext

Majority of the logic of smart contracts has to do with making assertions about certain properties of the ScriptContext. It contains a lot of useful information such as:

• When is the transaction?
• What will the inputs of the transactions be?
• What will the outputs of the transaction?

All of these things are contained in the ScriptContext object passed into the contract as the last argument. This section covers the most interesting parts of the Script Context - if you want to learn more check out the full documentation at the module description

ScriptContext

The ScriptContext is defined as:

@dataclass()
class ScriptContext(PlutusData):
    """
    Auxiliary information about the transaction and reason for invocation of the called script.
    """

    transaction: TxInfo
    redeemer: Anything
    purpose: ScriptPurpose

The redeemer is arbitrary information provided by the user during building the transaction. It can indicate how the user intends to use the contracts, e.g., for cancelling or executing a submitted order.

The second most important field in the ScriptContext is the transaction field which is of type TxInfo.

TxInfo

@dataclass()
class TxInfo(PlutusData):
    """
    A complex agglomeration of everything that could be of interest to the executed script, regarding the transaction
    that invoked the script
    """

    # The input UTXOs of the transaction.
    inputs: List[TxInInfo]
    # The reference UTXOs of the transaction.
    reference_inputs: List[TxInInfo]
    # The output UTXOs created by the transaction.
    outputs: List[TxOut]
    # Transaction fee to be payed for the transaction in Lovelace.
    fee: int
    # The value minted in the transaction.
    mint: Value
    certificates: List[Certificate]
    # Withdrawals from specific stake keys
    withdrawals: Dict[StakingCredential, int]
    # The range of time in which this transaction is valid
    validity_range: POSIXTimeRange
    # The signatures for the transaction.
    signatories: List[PubKeyHash]
    # All redeemers passed to all script invocations
    redeemers: Dict[ScriptPurpose, Redeemer]
    # All datums present in any inputs
    datums: Dict[DatumHash, Datum]
    # The ID of the transaction.
    id: TxId
    # metadata for governance actions
    votes: Dict[Voter, Dict[GovernanceActionId, Vote]]
    proposal_procedures: List[ProposalProcedure]
    current_treasury_amount: OptionalLovelace
    treasury_donation: OptionalLovelace

TxInInfo

This type contains data about a UTXO being used as a transaction input.

@dataclass()
class TxInInfo(PlutusData):
    """
    The plutus representation of an transaction output, that is consumed by the transaction.
    """

    out_ref: TxOutRef
    resolved: TxOut

TxOut

This type contains data about a UTXO.

@dataclass()
class TxOut(PlutusData):
    """
    The plutus representation of an transaction output, consisting of
    - address: address owning this output
    - value: tokens associated with this output
    - datum: datum associated with this output
    - reference_script: reference script associated with this output
    """

    address: Address
    value: Value
    datum: OutputDatum
    reference_script: Union[NoScriptHash, SomeScriptHash]