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 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 ID of asset being transferred
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, starting at 0
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 ID of asset being configured
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.global_num_uints() TealType.uint64 Maximum global integers in app schema
Txn.global_num_byte_slices() TealType.uint64 Maximum global byte strings in app schema
Txn.local_num_uints() TealType.uint64 Maximum local integers in app schema
Txn.local_num_byte_slices() TealType.uint64 Maximum local byte strings in app schema
Txn.extra_program_pages() TealType.uint64 Number of extra program pages for app
Txn.application_args TealType.bytes[] Array of application arguments
Txn.accounts TealType.bytes[] Array of application accounts
Txn.assets TealType.uint64[] Array of application assets
Txn.applications TealType.uint64[] Array of applications

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

Transaction Array Fields

Some of the exposed transaction fields are arrays with the type TealType.uint64[] or TealType.bytes[]. These fields are Txn.application_args, Txn.assets, Txn.accounts, and Txn.applications.

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 and Txn.applications

The Txn.accounts and Txn.applications arrays are special cases. Normal arrays in PyTeal are 0-indexed, but these are 1-indexed with special values at index 0.

For the accounts array, Txn.accounts[0] is always equivalent to Txn.sender().

For the applications array, Txn.applications[0] is always equivalent to Txn.application_id().

IMPORTANT: Since these arrays are 1-indexed, their lengths are handled differently. For example, if Txn.accounts.length() or Txn.applications.length() is 2, then indexes 0, 1, and 2 will be present. In fact, the index 0 will always evaluate to the special values above, even when length() is 0.

Atomic Transfer 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
Global.creator_address() TealType.bytes 32 byte address of the creator of the current application