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 |