Transaction Fields and Global Parameters¶

PyTeal smart contracts can access properties of the current transaction and the state of the blockchain when they are running.

Transaction Fields¶

Information about the current transaction being evaluated can be obtained using the Txn object. Below are the PyTeal expressions that refer to transaction fields:

Operator	Type	Notes
`Txn.sender()`	`TealType.bytes`	32 byte address
`Txn.fee()`	`TealType.uint64`	in microAlgos
`Txn.first_valid()`	`TealType.uint64`	round number
`Txn.last_valid()`	`TealType.uint64`	round number
`Txn.note()`	`TealType.bytes`	transaction note in bytes
`Txn.lease()`	`TealType.bytes`	transaction lease in bytes
`Txn.receiver()`	`TealType.bytes`	32 byte address
`Txn.amount()`	`TealType.uint64`	in microAlgos
`Txn.close_remainder_to()`	`TealType.bytes`	32 byte address
`Txn.vote_pk()`	`TealType.bytes`	32 byte address
`Txn.selection_pk()`	`TealType.bytes`	32 byte address
`Txn.vote_first()`	`TealType.uint64`
`Txn.vote_last()`	`TealType.uint64`
`Txn.vote_key_dilution()`	`TealType.uint64`
`Txn.type()`	`TealType.bytes`
`Txn.type_enum()`	`TealType.uint64`	see table below
`Txn.xfer_asset()`	`TealType.uint64`	asset ID
`Txn.asset_amount()`	`TealType.uint64`	value in Asset’s units
`Txn.asset_sender()`	`TealType.bytes`	32 byte address, causes clawback of all value if sender is the Clawback
`Txn.asset_receiver()`	`TealType.bytes`	32 byte address
`Txn.asset_close_to()`	`TealType.bytes`	32 byte address
`Txn.group_index()`	`TealType.uint64`	position of this transaction within a transaction group
`Txn.tx_id()`	`TealType.bytes`	the computed ID for this transaction, 32 bytes
`Txn.application_id()`	`TealType.uint64`
`Txn.on_completion()`	`TealType.uint64`
`Txn.approval_program()`	`TealType.bytes`
`Txn.clear_state_program()`	`TealType.bytes`
`Txn.rekey_to()`	`TealType.bytes`	32 byte address
`Txn.config_asset()`	`TealType.uint64`
`Txn.config_asset_total()`	`TealType.uint64`
`Txn.config_asset_decimals()`	`TealType.uint64`
`Txn.config_asset_default_frozen()`	`TealType.uint64`
`Txn.config_asset_unit_name()`	`TealType.bytes`
`Txn.config_asset_name()`	`TealType.bytes`
`Txn.config_asset_url()`	`TealType.bytes`
`Txn.config_asset_metadata_hash()`	`TealType.bytes`
`Txn.config_asset_manager()`	`TealType.bytes`	32 byte address
`Txn.config_asset_reserve()`	`TealType.bytes`	32 byte address
`Txn.config_asset_freeze()`	`TealType.bytes`	32 byte address
`Txn.config_asset_clawback()`	`TealType.bytes`	32 byte address
`Txn.freeze_asset()`	`TealType.uint64`
`Txn.freeze_asset_account()`	`TealType.bytes`	32 byte address
`Txn.freeze_asset_frozen()`	`TealType.uint64`
`Txn.application_args`	`TealType.bytes[]`	Array of application arguments
`Txn.accounts`	`TealType.bytes[]`	Array of additional application accounts

Transaction Type¶

The Txn.type_enum() values can be checked using the TxnType enum:

Value	Numerical Value	Type String	Description
`TxnType.Unknown`	`0`	unkown	unknown type, invalid
`TxnType.Payment`	`1`	pay	payment
`TxnType.KeyRegistration`	`2`	keyreg	key registration
`TxnType.AssetConfig`	`3`	acfg	asset config
`TxnType.AssetTransfer`	`4`	axfer	asset transfer
`TxnType.AssetFreeze`	`5`	afrz	asset freeze
`TxnType.ApplicationCall`	`6`	appl	application call

Tranasction Array Fields¶

Some of the exposed transaction fields are arrays with the type TealType.bytes[]. These fields are Txn.application_args and Txn.accounts.

The length of these array fields can be found using the .length() method, and individual items can be accesses using bracket notation. For example:

Txn.application_args.length() # get the number of application arguments in the transaction
Txn.application_args[0] # get the first application argument
Txn.application_args[1] # get the second application argument

Special case: `Txn.accounts`¶

The Txn.accounts is a special case array. Normal arrays in PyTeal are 0-indexed, but this one is 1-indexed with a special value at index 0, the sender’s address. That means if Txn.accounts.length() is 2, then indexes 0, 1, and 2 will be present. In fact, Txn.accounts[0] will always evaluate to the sender’s address, even when Txn.accounts.length() is 0.

Atomic Tranfer Groups¶

Atomic Transfers are irreducible batch transactions that allow groups of transactions to be submitted at one time. If any of the transactions fail, then all the transactions will fail. PyTeal allows programs to access information about the transactions in an atomic transfer group using the Gtxn object. This object acts like a list of TxnObject, meaning all of the above transaction fields on Txn are available on the elements of Gtxn. For example:

Gtxn[0].sender() # get the sender of the first transaction in the atomic transfer group
Gtxn[1].receiver() # get the receiver of the second transaction in the atomic transfer group

Gtxn is zero-indexed and the maximum size of an atomic transfer group is 16. The size of the current transaction group is available as Global.group_size(). A standalone transaction will have a group size of 1.

To find the current transaction’s index in the transfer group, use Txn.group_index(). If the current transaction is standalone, it’s group index will be 0.

Global Parameters¶

Information about the current state of the blockchain can be obtained using the following Global expressions:

Operator	Type	Notes
`Global.min_txn_fee()`	`TealType.uint64`	in microAlgos
`Global.min_balance()`	`TealType.uint64`	in mircoAlgos
`Global.max_txn_life()`	`TealType.uint64`	number of rounds
`Global.zero_address()`	`TealType.bytes`	32 byte address of all zero bytes
`Global.group_size()`	`TealType.uint64`	number of txns in this atomic transaction group, at least 1
`Global.logic_sig_version()`	`TealType.uint64`	the maximum supported TEAL version
`Global.round()`	`TealType.uint64`	the current round number
`Global.latest_timestamp()`	`TealType.uint64`	the latest confirmed block UNIX timestamp
`Global.current_application_id()`	`TealType.uint64`	the ID of the current application executing

Transaction Fields and Global Parameters¶