.. index:: function, built-in;
Vyper provides a collection of built-in functions available in the global namespace of all contracts.
.. py:function:: bitwise_and(x: uint256, y: uint256) -> uint256
Perform a "bitwise and" operation. Each bit of the output is 1 if the corresponding bit of ``x`` AND of ``y`` is 1, otherwise it is 0.
.. code-block:: python
@external
@view
def foo(x: uint256, y: uint256) -> uint256:
return bitwise_and(x, y)
.. code-block:: python
>>> ExampleContract.foo(31337, 8008135)
12353
Note
This function has been deprecated from version 0.3.4 onwards. Please use the & operator instead.
.. py:function:: bitwise_not(x: uint256) -> uint256
Return the bitwise complement of ``x`` - the number you get by switching each 1 for a 0 and each 0 for a 1.
.. code-block:: python
@external
@view
def foo(x: uint256) -> uint256:
return bitwise_not(x)
.. code-block:: python
>>> ExampleContract.foo(0)
115792089237316195423570985008687907853269984665640564039457584007913129639935
Note
This function has been deprecated from version 0.3.4 onwards. Please use the ~ operator instead.
.. py:function:: bitwise_or(x: uint256, y: uint256) -> uint256
Perform a "bitwise or" operation. Each bit of the output is 0 if the corresponding bit of ``x`` AND of ``y`` is 0, otherwise it is 1.
.. code-block:: python
@external
@view
def foo(x: uint256, y: uint256) -> uint256:
return bitwise_or(x, y)
.. code-block:: python
>>> ExampleContract.foo(31337, 8008135)
8027119
Note
This function has been deprecated from version 0.3.4 onwards. Please use the | operator instead.
.. py:function:: bitwise_xor(x: uint256, y: uint256) -> uint256
Perform a "bitwise exclusive or" operation. Each bit of the output is the same as the corresponding bit in ``x`` if that bit in ``y`` is 0, and it is the complement of the bit in ``x`` if that bit in ``y`` is 1.
.. code-block:: python
@external
@view
def foo(x: uint256, y: uint256) -> uint256:
return bitwise_xor(x, y)
.. code-block:: python
>>> ExampleContract.foo(31337, 8008135)
8014766
Note
This function has been deprecated from version 0.3.4 onwards. Please use the ^ operator instead.
.. py:function:: shift(x: int256 | uint256, _shift: integer) -> uint256
Return ``x`` with the bits shifted ``_shift`` places. A positive ``_shift`` value equals a left shift, a negative value is a right shift.
.. code-block:: python
@external
@view
def foo(x: uint256, y: int128) -> uint256:
return shift(x, y)
.. code-block:: python
>>> ExampleContract.foo(2, 8)
512
Note
This function has been deprecated from version 0.3.8 onwards. Please use the << and >> operators instead.
Vyper has three built-ins for contract creation; all three contract creation built-ins rely on the code to deploy already being stored on-chain, but differ in call vs deploy overhead, and whether or not they invoke the constructor of the contract to be deployed. The following list provides a short summary of the differences between them.
create_minimal_proxy_to(target: address, ...)- Creates an immutable proxy to
target - Expensive to call (incurs a single
DELEGATECALLoverhead on every invocation), cheap to create (since it only deploysEIP-1167forwarder bytecode) - Does not have the ability to call a constructor
- Does not check that there is code at
target(allows one to deploy proxies counterfactually)
- Creates an immutable proxy to
create_copy_of(target: address, ...)- Creates a byte-for-byte copy of runtime code stored at
target - Cheap to call (no
DELEGATECALLoverhead), expensive to create (200 gas per deployed byte) - Does not have the ability to call a constructor
- Performs an
EXTCODESIZEcheck to check there is code attarget
- Creates a byte-for-byte copy of runtime code stored at
create_from_blueprint(target: address, ...)- Deploys a contract using the initcode stored at
target - Cheap to call (no
DELEGATECALLoverhead), expensive to create (200 gas per deployed byte) - Invokes constructor, requires a special "blueprint" contract to be deployed
- Performs an
EXTCODESIZEcheck to check there is code attarget
- Deploys a contract using the initcode stored at
.. py:function:: create_minimal_proxy_to(target: address, value: uint256 = 0[, salt: bytes32]) -> address
Deploys a small, EIP1167-compliant "minimal proxy contract" that duplicates the logic of the contract at ``target``, but has its own state since every call to ``target`` is made using ``DELEGATECALL`` to ``target``. To the end user, this should be indistinguishable from an independently deployed contract with the same code as ``target``.
* ``target``: Address of the contract to proxy to
* ``value``: The wei value to send to the new contract address (Optional, default 0)
* ``salt``: A ``bytes32`` value utilized by the deterministic ``CREATE2`` opcode (Optional, if not supplied, ``CREATE`` is used)
Returns the address of the newly created proxy contract. If the create operation fails (for instance, in the case of a ``CREATE2`` collision), execution will revert.
.. code-block:: python
@external
def foo(target: address) -> address:
return create_minimal_proxy_to(target)
Note
It is very important that the deployed contract at target is code you know and trust, and does not implement the selfdestruct opcode or have upgradeable code as this will affect the operation of the proxy contract.
Note
There is no runtime check that there is code already deployed at target (since a proxy may be deployed counterfactually). Most applications may want to insert this check.
Note
Before version 0.3.4, this function was named create_forwarder_to.
.. py:function:: create_copy_of(target: address, value: uint256 = 0[, salt: bytes32]) -> address
Create a physical copy of the runtime code at ``target``. The code at ``target`` is byte-for-byte copied into a newly deployed contract.
* ``target``: Address of the contract to copy
* ``value``: The wei value to send to the new contract address (Optional, default 0)
* ``salt``: A ``bytes32`` value utilized by the deterministic ``CREATE2`` opcode (Optional, if not supplied, ``CREATE`` is used)
Returns the address of the created contract. If the create operation fails (for instance, in the case of a ``CREATE2`` collision), execution will revert. If there is no code at ``target``, execution will revert.
.. code-block:: python
@external
def foo(target: address) -> address:
return create_copy_of(target)
Note
The implementation of create_copy_of assumes that the code at target is smaller than 16MB. While this is much larger than the EIP-170 constraint of 24KB, it is a conservative size limit intended to future-proof deployer contracts in case the EIP-170 constraint is lifted. If the code at target is larger than 16MB, the behavior of create_copy_of is undefined.
.. py:function:: create_from_blueprint(target: address, *args, value: uint256 = 0, raw_args: bool = False, code_offset: int = 0, [, salt: bytes32]) -> address
Copy the code of ``target`` into memory and execute it as initcode. In other words, this operation interprets the code at ``target`` not as regular runtime code, but directly as initcode. The ``*args`` are interpreted as constructor arguments, and are ABI-encoded and included when executing the initcode.
* ``target``: Address of the blueprint to invoke
* ``*args``: Constructor arguments to forward to the initcode.
* ``value``: The wei value to send to the new contract address (Optional, default 0)
* ``raw_args``: If ``True``, ``*args`` must be a single ``Bytes[...]`` argument, which will be interpreted as a raw bytes buffer to forward to the create operation (which is useful for instance, if pre- ABI-encoded data is passed in from elsewhere). (Optional, default ``False``)
* ``code_offset``: The offset to start the ``EXTCODECOPY`` from (Optional, default 0)
* ``salt``: A ``bytes32`` value utilized by the deterministic ``CREATE2`` opcode (Optional, if not supplied, ``CREATE`` is used)
Returns the address of the created contract. If the create operation fails (for instance, in the case of a ``CREATE2`` collision), execution will revert. If ``code_offset >= target.codesize`` (ex. if there is no code at ``target``), execution will revert.
.. code-block:: python
@external
def foo(blueprint: address) -> address:
arg1: uint256 = 18
arg2: String[32] = "some string"
return create_from_blueprint(blueprint, arg1, arg2, code_offset=1)
Note
To properly deploy a blueprint contract, special deploy bytecode must be used. The output of vyper -f blueprint_bytecode will produce bytecode which deploys an ERC-5202 compatible blueprint.
Warning
It is recommended to deploy blueprints with the ERC-5202 preamble 0xFE7100 to guard them from being called as regular contracts. This is particularly important for factories where the constructor has side effects (including SELFDESTRUCT!), as those could get executed by anybody calling the blueprint contract directly. The code_offset= kwarg is provided to enable this pattern:
@external
def foo(blueprint: address) -> address:
# `blueprint` is a blueprint contract with some known preamble b"abcd..."
return create_from_blueprint(blueprint, code_offset=<preamble length>).. py:function:: raw_call(to: address, data: Bytes, max_outsize: uint256 = 0, gas: uint256 = gasLeft, value: uint256 = 0, is_delegate_call: bool = False, is_static_call: bool = False, revert_on_failure: bool = True) -> Bytes[max_outsize]
Call to the specified Ethereum address.
* ``to``: Destination address to call to
* ``data``: Data to send to the destination address
* ``max_outsize``: Maximum length of the bytes array returned from the call. If the returned call data exceeds this length, only this number of bytes is returned. (Optional, default ``0``)
* ``gas``: The amount of gas to attach to the call. (Optional, defaults to ``msg.gas``).
* ``value``: The wei value to send to the address (Optional, default ``0``)
* ``is_delegate_call``: If ``True``, the call will be sent as ``DELEGATECALL`` (Optional, default ``False``)
* ``is_static_call``: If ``True``, the call will be sent as ``STATICCALL`` (Optional, default ``False``)
* ``revert_on_failure``: If ``True``, the call will revert on a failure, otherwise ``success`` will be returned (Optional, default ``True``)
.. note::
Returns the data returned by the call as a ``Bytes`` list, with ``max_outsize`` as the max length. The actual size of the returned data may be less than ``max_outsize``. You can use ``len`` to obtain the actual size.
Returns nothing if ``max_outsize`` is omitted or set to ``0``.
Returns ``success`` in a tuple with return value if ``revert_on_failure`` is set to ``False``.
.. code-block:: python
@external
@payable
def foo(_target: address) -> Bytes[32]:
response: Bytes[32] = raw_call(_target, method_id("someMethodName()"), max_outsize=32, value=msg.value)
return response
@external
@payable
def bar(_target: address) -> Bytes[32]:
success: bool = False
response: Bytes[32] = b""
x: uint256 = 123
success, response = raw_call(
_target,
_abi_encode(x, method_id=method_id("someMethodName(uint256)")),
max_outsize=32,
value=msg.value,
revert_on_failure=False
)
assert success
return response
.. note::
Regarding "forwarding all gas", note that, while Vyper will provide ``msg.gas`` to the call, in practice, there are some subtleties around forwarding all remaining gas on the EVM which are out of scope of this documentation and could be subject to change. For instance, see the language in EIP-150 around "all but one 64th".
.. py:function:: raw_log(topics: bytes32[4], data: Union[Bytes, bytes32]) -> None
Provides low level access to the ``LOG`` opcodes, emitting a log without having to specify an ABI type.
* ``topics``: List of ``bytes32`` log topics. The length of this array determines which opcode is used.
* ``data``: Unindexed event data to include in the log. May be given as ``Bytes`` or ``bytes32``.
.. code-block:: python
@external
def foo(_topic: bytes32, _data: Bytes[100]):
raw_log([_topic], _data)
.. py:function:: raw_revert(data: Bytes) -> None
Provides low level access to the ``REVERT`` opcode, reverting execution with the specified data returned.
* ``data``: Data representing the error message causing the revert.
.. code-block:: python
@external
def foo(_data: Bytes[100]):
raw_revert(_data)
.. py:function:: selfdestruct(to: address) -> None
Trigger the ``SELFDESTRUCT`` opcode (``0xFF``), causing the contract to be destroyed.
* ``to``: Address to forward the contract's ether balance to
.. warning::
This method deletes the contract from the blockchain. All non-ether assets associated with this contract are "burned" and the contract is no longer accessible.
.. note::
This function has been deprecated from version 0.3.8 onwards. The underlying opcode will eventually undergo breaking changes, and its use is not recommended.
.. code-block:: python
@external
def do_the_needful():
selfdestruct(msg.sender)
.. py:function:: send(to: address, value: uint256, gas: uint256 = 0) -> None
Send ether from the contract to the specified Ethereum address.
* ``to``: The destination address to send ether to
* ``value``: The wei value to send to the address
* ``gas``: The amount of gas (the "stipend") to attach to the call. If not set, the stipend defaults to 0.
.. note::
The amount to send is always specified in ``wei``.
.. code-block:: python
@external
def foo(_receiver: address, _amount: uint256, gas: uint256):
send(_receiver, _amount, gas=gas)
.. py:function:: ecadd(a: uint256[2], b: uint256[2]) -> uint256[2]
Take two points on the Alt-BN128 curve and add them together.
.. code-block:: python
@external
@view
def foo(x: uint256[2], y: uint256[2]) -> uint256[2]:
return ecadd(x, y)
.. code-block:: python
>>> ExampleContract.foo([1, 2], [1, 2])
[
1368015179489954701390400359078579693043519447331113978918064868415326638035,
9918110051302171585080402603319702774565515993150576347155970296011118125764,
]
.. py:function:: ecmul(point: uint256[2], scalar: uint256) -> uint256[2]
Take a point on the Alt-BN128 curve (``p``) and a scalar value (``s``), and return the result of adding the point to itself ``s`` times, i.e. ``p * s``.
* ``point``: Point to be multiplied
* ``scalar``: Scalar value
.. code-block:: python
@external
@view
def foo(point: uint256[2], scalar: uint256) -> uint256[2]:
return ecmul(point, scalar)
.. code-block:: python
>>> ExampleContract.foo([1, 2], 3)
[
3353031288059533942658390886683067124040920775575537747144343083137631628272,
19321533766552368860946552437480515441416830039777911637913418824951667761761,
]
.. py:function:: ecrecover(hash: bytes32, v: uint256 | uint8, r: uint256 | bytes32, s: uint256 | bytes32) -> address
Recover the address associated with the public key from the given elliptic curve signature.
* ``r``: first 32 bytes of signature
* ``s``: second 32 bytes of signature
* ``v``: final 1 byte of signature
Returns the associated address, or ``empty(address)`` on error.
.. note::
Prior to Vyper ``0.3.10``, the ``ecrecover`` function could return an undefined (possibly nonzero) value for invalid inputs to ``ecrecover``. For more information, please see `GHSA-f5x6-7qgp-jhf3 <https://github.com/vyperlang/vyper/security/advisories/GHSA-f5x6-7qgp-jhf3>`_.
.. code-block:: python
@external
@view
def foo(hash: bytes32, v: uint8, r:bytes32, s:bytes32) -> address:
return ecrecover(hash, v, r, s)
@external
@view
def foo(hash: bytes32, v: uint256, r:uint256, s:uint256) -> address:
return ecrecover(hash, v, r, s)
.. code-block:: python
>>> ExampleContract.foo('0x6c9c5e133b8aafb2ea74f524a5263495e7ae5701c7248805f7b511d973dc7055',
28,
78616903610408968922803823221221116251138855211764625814919875002740131251724,
37668412420813231458864536126575229553064045345107737433087067088194345044408
)
'0x9eE53ad38Bb67d745223a4257D7d48cE973FeB7A'
.. py:function:: keccak256(_value) -> bytes32
Return a ``keccak256`` hash of the given value.
* ``_value``: Value to hash. Can be a ``String``, ``Bytes``, or ``bytes32``.
.. code-block:: python
@external
@view
def foo(_value: Bytes[100]) -> bytes32
return keccak256(_value)
.. code-block:: python
>>> ExampleContract.foo(b"potato")
0x9e159dfcfe557cc1ca6c716e87af98fdcb94cd8c832386d0429b2b7bec02754f
.. py:function:: sha256(_value) -> bytes32
Return a ``sha256`` (SHA2 256-bit output) hash of the given value.
* ``_value``: Value to hash. Can be a ``String``, ``Bytes``, or ``bytes32``.
.. code-block:: python
@external
@view
def foo(_value: Bytes[100]) -> bytes32
return sha256(_value)
.. code-block:: python
>>> ExampleContract.foo(b"potato")
0xe91c254ad58860a02c788dfb5c1a65d6a8846ab1dc649631c7db16fef4af2dec
.. py:function:: concat(a, b, *args) -> Union[Bytes, String]
Take 2 or more bytes arrays of type ``bytesM``, ``Bytes`` or ``String`` and combine them into a single value.
If the input arguments are ``String`` the return type is ``String``. Otherwise the return type is ``Bytes``.
.. code-block:: python
@external
@view
def foo(a: String[5], b: String[5], c: String[5]) -> String[100]:
return concat(a, " ", b, " ", c, "!")
.. code-block:: python
>>> ExampleContract.foo("why","hello","there")
"why hello there!"
.. py:function:: convert(value, type_) -> Any
Converts a variable or literal from one type to another.
* ``value``: Value to convert
* ``type_``: The destination type to convert to (e.g., ``bool``, ``decimal``, ``int128``, ``uint256`` or ``bytes32``)
Returns a value of the type specified by ``type_``.
For more details on available type conversions, see :ref:`type_conversions`.
.. py:function:: uint2str(value: unsigned integer) -> String
Returns an unsigned integer's string representation.
* ``value``: Unsigned integer to convert.
Returns the string representation of ``value``.
.. code-block:: python
@external
@view
def foo(b: uint256) -> String[78]:
return uint2str(b)
.. code-block:: python
>>> ExampleContract.foo(420)
"420"
.. py:function:: extract32(b: Bytes, start: uint256, output_type=bytes32) -> Any
Extract a value from a ``Bytes`` list.
* ``b``: ``Bytes`` list to extract from
* ``start``: Start point to extract from
* ``output_type``: Type of output (``bytesM``, ``integer``, or ``address``). Defaults to ``bytes32``.
Returns a value of the type specified by ``output_type``.
.. code-block:: python
@external
@view
def foo(b: Bytes[32]) -> address:
return extract32(b, 0, output_type=address)
.. code-block:: python
>>> ExampleContract.foo("0x0000000000000000000000009f8F72aA9304c8B593d555F12eF6589cC3A579A2")
"0x9f8F72aA9304c8B593d555F12eF6589cC3A579A2"
.. py:function:: slice(b: Union[Bytes, bytes32, String], start: uint256, length: uint256) -> Union[Bytes, String]
Copy a list of bytes and return a specified slice.
* ``b``: value being sliced
* ``start``: start position of the slice
* ``length``: length of the slice
If the value being sliced is a ``Bytes`` or ``bytes32``, the return type is ``Bytes``. If it is a ``String``, the return type is ``String``.
.. code-block:: python
@external
@view
def foo(s: String[32]) -> String[5]:
return slice(s, 4, 5)
.. code-block:: python
>>> ExampleContract.foo("why hello! how are you?")
"hello"
.. py:function:: abs(value: int256) -> int256
Return the absolute value of a signed integer.
* ``value``: Integer to return the absolute value of
.. code-block:: python
@external
@view
def foo(value: int256) -> int256:
return abs(value)
.. code-block:: python
>>> ExampleContract.foo(-31337)
31337
.. py:function:: ceil(value: decimal) -> int256
Round a decimal up to the nearest integer.
* ``value``: Decimal value to round up
.. code-block:: python
@external
@view
def foo(x: decimal) -> int256:
return ceil(x)
.. code-block:: python
>>> ExampleContract.foo(3.1337)
4
.. py:function:: epsilon(typename) -> Any
Returns the smallest non-zero value for a decimal type.
* ``typename``: Name of the decimal type (currently only ``decimal``)
.. code-block:: python
@external
@view
def foo() -> decimal:
return epsilon(decimal)
.. code-block:: python
>>> ExampleContract.foo()
Decimal('1E-10')
.. py:function:: floor(value: decimal) -> int256
Round a decimal down to the nearest integer.
* ``value``: Decimal value to round down
.. code-block:: python
@external
@view
def foo(x: decimal) -> int256:
return floor(x)
.. code-block:: python
>>> ExampleContract.foo(3.1337)
3
.. py:function:: max(a: numeric, b: numeric) -> numeric
Return the greater value of ``a`` and ``b``. The input values may be any numeric type as long as they are both of the same type. The output value is of the same type as the input values.
.. code-block:: python
@external
@view
def foo(a: uint256, b: uint256) -> uint256:
return max(a, b)
.. code-block:: python
>>> ExampleContract.foo(23, 42)
42
.. py:function:: max_value(type_) -> numeric
Returns the maximum value of the numeric type specified by ``type_`` (e.g., ``int128``, ``uint256``, ``decimal``).
.. code-block:: python
@external
@view
def foo() -> int256:
return max_value(int256)
.. code-block:: python
>>> ExampleContract.foo()
57896044618658097711785492504343953926634992332820282019728792003956564819967
.. py:function:: min(a: numeric, b: numeric) -> numeric
Returns the lesser value of ``a`` and ``b``. The input values may be any numeric type as long as they are both of the same type. The output value is of the same type as the input values.
.. code-block:: python
@external
@view
def foo(a: uint256, b: uint256) -> uint256:
return min(a, b)
.. code-block:: python
>>> ExampleContract.foo(23, 42)
23
.. py:function:: min_value(type_) -> numeric
Returns the minimum value of the numeric type specified by ``type_`` (e.g., ``int128``, ``uint256``, ``decimal``).
.. code-block:: python
@external
@view
def foo() -> int256:
return min_value(int256)
.. code-block:: python
>>> ExampleContract.foo()
-57896044618658097711785492504343953926634992332820282019728792003956564819968
.. py:function:: pow_mod256(a: uint256, b: uint256) -> uint256
Return the result of ``a ** b % (2 ** 256)``.
This method is used to perform exponentiation without overflow checks.
.. code-block:: python
@external
@view
def foo(a: uint256, b: uint256) -> uint256:
return pow_mod256(a, b)
.. code-block:: python
>>> ExampleContract.foo(2, 3)
8
>>> ExampleContract.foo(100, 100)
59041770658110225754900818312084884949620587934026984283048776718299468660736
.. py:function:: sqrt(d: decimal) -> decimal
Return the square root of the provided decimal number, using the Babylonian square root algorithm.
.. code-block:: python
@external
@view
def foo(d: decimal) -> decimal:
return sqrt(d)
.. code-block:: python
>>> ExampleContract.foo(9.0)
3.0
.. py:function:: isqrt(x: uint256) -> uint256
Return the (integer) square root of the provided integer number, using the Babylonian square root algorithm. The rounding mode is to round down to the nearest integer. For instance, ``isqrt(101) == 10``.
.. code-block:: python
@external
@view
def foo(x: uint256) -> uint256:
return isqrt(x)
.. code-block:: python
>>> ExampleContract.foo(101)
10
.. py:function:: uint256_addmod(a: uint256, b: uint256, c: uint256) -> uint256
Return the modulo of ``(a + b) % c``. Reverts if ``c == 0``. As this built-in function is intended to provides access to the underlying ``ADDMOD`` opcode, all intermediate calculations of this operation are not subject to the ``2 ** 256`` modulo according to the EVM specifications.
.. code-block:: python
@external
@view
def foo(a: uint256, b: uint256, c: uint256) -> uint256:
return uint256_addmod(a, b, c)
.. code-block:: python
>>> (6 + 13) % 8
3
>>> ExampleContract.foo(6, 13, 8)
3
.. py:function:: uint256_mulmod(a: uint256, b: uint256, c: uint256) -> uint256
Return the modulo from ``(a * b) % c``. Reverts if ``c == 0``. As this built-in function is intended to provides access to the underlying ``MULMOD`` opcode, all intermediate calculations of this operation are not subject to the ``2 ** 256`` modulo according to the EVM specifications.
.. code-block:: python
@external
@view
def foo(a: uint256, b: uint256, c: uint256) -> uint256:
return uint256_mulmod(a, b, c)
.. code-block:: python
>>> (11 * 2) % 5
2
>>> ExampleContract.foo(11, 2, 5)
2
.. py:function:: unsafe_add(x: integer, y: integer) -> integer
Add ``x`` and ``y``, without checking for overflow. ``x`` and ``y`` must both be integers of the same type. If the result exceeds the bounds of the input type, it will be wrapped.
.. code-block:: python
@external
@view
def foo(x: uint8, y: uint8) -> uint8:
return unsafe_add(x, y)
@external
@view
def bar(x: int8, y: int8) -> int8:
return unsafe_add(x, y)
.. code-block:: python
>>> ExampleContract.foo(1, 1)
2
>>> ExampleContract.foo(255, 255)
254
>>> ExampleContract.bar(127, 127)
-2
Note
Performance note: for the native word types of the EVM uint256 and int256, this will compile to a single ADD instruction, since the EVM natively wraps addition on 256-bit words.
.. py:function:: unsafe_sub(x: integer, y: integer) -> integer
Subtract ``x`` and ``y``, without checking for overflow. ``x`` and ``y`` must both be integers of the same type. If the result underflows the bounds of the input type, it will be wrapped.
.. code-block:: python
@external
@view
def foo(x: uint8, y: uint8) -> uint8:
return unsafe_sub(x, y)
@external
@view
def bar(x: int8, y: int8) -> int8:
return unsafe_sub(x, y)
.. code-block:: python
>>> ExampleContract.foo(4, 3)
1
>>> ExampleContract.foo(0, 1)
255
>>> ExampleContract.bar(-128, 1)
127
Note
Performance note: for the native word types of the EVM uint256 and int256, this will compile to a single SUB instruction, since the EVM natively wraps subtraction on 256-bit words.
.. py:function:: unsafe_mul(x: integer, y: integer) -> integer
Multiply ``x`` and ``y``, without checking for overflow. ``x`` and ``y`` must both be integers of the same type. If the result exceeds the bounds of the input type, it will be wrapped.
.. code-block:: python
@external
@view
def foo(x: uint8, y: uint8) -> uint8:
return unsafe_mul(x, y)
@external
@view
def bar(x: int8, y: int8) -> int8:
return unsafe_mul(x, y)
.. code-block:: python
>>> ExampleContract.foo(1, 1)
1
>>> ExampleContract.foo(255, 255)
1
>>> ExampleContract.bar(-128, -128)
0
>>> ExampleContract.bar(127, -128)
-128
Note
Performance note: for the native word types of the EVM uint256 and int256, this will compile to a single MUL instruction, since the EVM natively wraps multiplication on 256-bit words.
.. py:function:: unsafe_div(x: integer, y: integer) -> integer
Divide ``x`` and ``y``, without checking for division-by-zero. ``x`` and ``y`` must both be integers of the same type. If the denominator is zero, the result will (following EVM semantics) be zero.
.. code-block:: python
@external
@view
def foo(x: uint8, y: uint8) -> uint8:
return unsafe_div(x, y)
@external
@view
def bar(x: int8, y: int8) -> int8:
return unsafe_div(x, y)
.. code-block:: python
>>> ExampleContract.foo(1, 1)
1
>>> ExampleContract.foo(1, 0)
0
>>> ExampleContract.bar(-128, -1)
-128
Note
Performance note: this will compile to a single SDIV or DIV instruction, depending on if the inputs are signed or unsigned (respectively).
.. py:function:: as_wei_value(_value, unit: str) -> uint256
Take an amount of ether currency specified by a number and a unit and return the integer quantity of wei equivalent to that amount.
* ``_value``: Value for the ether unit. Any numeric type may be used, however the value cannot be negative.
* ``unit``: Ether unit name (e.g. ``"wei"``, ``"ether"``, ``"gwei"``, etc.) indicating the denomination of ``_value``. Must be given as a literal string.
.. code-block:: python
@external
@view
def foo(s: String[32]) -> uint256:
return as_wei_value(1.337, "ether")
.. code-block:: python
>>> ExampleContract.foo(1)
1337000000000000000
.. py:function:: blockhash(block_num: uint256) -> bytes32
Return the hash of the block at the specified height.
.. note::
The EVM only provides access to the most recent 256 blocks. This function reverts if the block number is greater than or equal to the current block number or more than 256 blocks behind the current block.
.. code-block:: python
@external
@view
def foo() -> bytes32:
return blockhash(block.number - 16)
.. code-block:: python
>>> ExampleContract.foo()
0xf3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855
.. py:function:: empty(typename) -> Any
Return a value which is the default (zero-ed) value of its type. Useful for initializing new memory variables.
* ``typename``: Name of the type, except ``HashMap[_KeyType, _ValueType]``
.. code-block:: python
@external
@view
def foo():
x: uint256[2][5] = empty(uint256[2][5])
.. py:function:: len(b: Union[Bytes, String, DynArray[_Type, _Integer]]) -> uint256
Return the length of a given ``Bytes``, ``String`` or ``DynArray[_Type, _Integer]``.
.. code-block:: python
@external
@view
def foo(s: String[32]) -> uint256:
return len(s)
.. code-block:: python
>>> ExampleContract.foo("hello")
5
.. py:function:: method_id(method, output_type: type = Bytes[4]) -> Union[Bytes[4], bytes4]
Takes a function declaration and returns its method_id (used in data field to call it).
* ``method``: Method declaration as given as a literal string
* ``output_type``: The type of output (``Bytes[4]`` or ``bytes4``). Defaults to ``Bytes[4]``.
Returns a value of the type specified by ``output_type``.
.. code-block:: python
@external
@view
def foo() -> Bytes[4]:
return method_id('transfer(address,uint256)', output_type=Bytes[4])
.. code-block:: python
>>> ExampleContract.foo()
0xa9059cbb
.. py:function:: _abi_encode(*args, ensure_tuple: bool = True) -> Bytes[<depends on input>]
Takes a variable number of args as input, and returns the ABIv2-encoded bytestring. Used for packing arguments to raw_call, EIP712 and other cases where a consistent and efficient serialization method is needed.
Once this function has seen more use we provisionally plan to put it into the ``ethereum.abi`` namespace.
* ``*args``: Arbitrary arguments
* ``ensure_tuple``: If set to True, ensures that even a single argument is encoded as a tuple. In other words, ``bytes`` gets encoded as ``(bytes,)``, and ``(bytes,)`` gets encoded as ``((bytes,),)`` This is the calling convention for Vyper and Solidity functions. Except for very specific use cases, this should be set to True. Must be a literal.
* ``method_id``: A literal hex or Bytes[4] value to append to the beginning of the abi-encoded bytestring.
Returns a bytestring whose max length is determined by the arguments. For example, encoding a ``Bytes[32]`` results in a ``Bytes[64]`` (first word is the length of the bytestring variable).
.. code-block:: python
@external
@view
def foo() -> Bytes[132]:
x: uint256 = 1
y: Bytes[32] = b"234"
return _abi_encode(x, y, method_id=method_id("foo()"))
.. code-block:: python
>>> ExampleContract.foo().hex()
"c2985578"
"0000000000000000000000000000000000000000000000000000000000000001"
"0000000000000000000000000000000000000000000000000000000000000040"
"0000000000000000000000000000000000000000000000000000000000000003"
"3233340000000000000000000000000000000000000000000000000000000000"
.. py:function:: _abi_decode(b: Bytes, output_type: type_, unwrap_tuple: bool = True) -> Any
Takes a byte array as input, and returns the decoded values according to the specified output types. Used for unpacking ABIv2-encoded values.
Once this function has seen more use we provisionally plan to put it into the ``ethereum.abi`` namespace.
* ``b``: A byte array of a length that is between the minimum and maximum ABIv2 size bounds of the ``output type``.
* ``output_type``: Name of the output type, or tuple of output types, to be decoded.
* ``unwrap_tuple``: If set to True, the input is decoded as a tuple even if only one output type is specified. In other words, ``_abi_decode(b, Bytes[32])`` gets decoded as ``(Bytes[32],)``. This is the convention for ABIv2-encoded values generated by Vyper and Solidity functions. Except for very specific use cases, this should be set to True. Must be a literal.
Returns the decoded value(s), with type as specified by `output_type`.
.. code-block:: python
@external
@view
def foo(someInput: Bytes[128]) -> (uint256, Bytes[32]):
x: uint256 = empty(uint256)
y: Bytes[32] = empty(Bytes[32])
x, y = _abi_decode(someInput, (uint256, Bytes[32]))
return x, y
.. py:function:: print(*args, hardhat_compat=False) -> None
"prints" the arguments by issuing a static call to the "console" address, ``0x000000000000000000636F6E736F6C652E6C6F67``. This is supported by some smart contract development frameworks.
The default mode works natively with titanoboa. For hardhat-style frameworks, use ``hardhat_compat=True)``.
Note
Issuing of the static call is NOT mode-dependent (that is, it is not removed from production code), although the compiler will issue a warning whenever print is used.