Built in Functions

Vyper provides a collection of built in functions available in the global namespace of all contracts.

floor(value: decimal) → int128

Rounds a decimal down to the nearest integer.

  • value: Decimal value to round down
ceil(value: decimal) → int128

Rounds a decimal up to the nearest integer.

  • value: Decimal value to round up
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 (bool, decimal, int128, uint256 or bytes32)

Returns a value of the type specified by type_.

For more details on available type conversions, see Type Conversions.

clear(var: Any) → None

Clears a variable’s contents to the default value of its type.

  • var: Variable to clear
as_wei_value(value: int, unit: str) → wei_value

Takes an amount of ether currency specified by a number and a unit and returns the integer quantity of wei equivalent to that amount.

  • value: Value for the ether unit
  • unit: Ether unit name (e.g. "wei", "ether", "gwei", etc.)
as_unitless_number(value) → int

Converts a int128, uint256, or decimal value with units into one without units (used for assignment and math).

slice(b: bytes, start: int128, length: int128) → bytes

Copies a list of bytes and returns a specified slice.

  • b: bytes or bytes32 to be sliced
  • start: start position of the slice
  • length: length of the slice
len(b: bytes) → int128

Returns the length of a given bytes list.

concat(a, b, *args) → bytes

Takes 2 or more bytes arrays of type bytes32 or bytes and combines them into a single bytes list.

keccak256(value) → bytes32

Returns a keccak256 hash of the given value.

  • value: Value to hash. Can be str_literal, bytes, or bytes32.
sha256(value) → bytes32

Returns a sha256 (SHA2 256bit output) hash of the given value.

  • value: Value to hash. Can be str_literal, bytes, or bytes32.
sqrt(d: decimal) → decimal

Returns the square root of the provided decimal number, using the Babylonian square root algorithm.

method_id(method, type_) → Union[bytes32, bytes[4]]

Takes a function declaration and returns its method_id (used in data field to call it).

  • method: Method declaration as str_literal
  • type_: Type of output (bytes32 or bytes[4])

Returns a value of the type specified by type_.

ecrecover(hash: bytes32, v: uint256, r: uint256, s: uint256) → address

Takes a signed hash and vrs and returns the public key of the signer.

ecadd(a: uint256[2], b: uint256[2]) → uint256[2]

Takes two points on the Alt-BN128 curve and adds them together.

ecmul(point: uint256[2], scalar: uint256) → uint256[2]

Takes a point on the Alt-BN128 curve (p) and a scalar value (s), and returns the result of adding the point to itself s times, i.e. p * s.

  • point: Point to be multiplied
  • scalar: Scalar value
extract32(b: bytes, start: int128, type_=bytes32) → Union[bytes32, int128, address]

Extracts a value from a bytes list.

  • b: bytes list to extract from
  • start: Start point to extract from
  • type_: Type of output (bytes32, int128, or address). Defaults to bytes32.

Returns a value of the type specified by type_.

RLPList(b: bytes, types_list: List) → LLLnode

Takes encoded RLP data and an unencoded list of types.

  • b: Encoded data
  • types_list: List of types

Example usage:

vote_msg: bytes <= 1024 = ...

values = RLPList(vote_msg, [int128, int128, bytes32, bytes, bytes])

var1: int128 = values[0]
var2: int128 = values[1]
var3: bytes32 = values[2]
var4: bytes <= 1024 = values[3]
var5: bytes <= 1024 = values[4]

RLP decoder needs to be deployed if one wishes to use it outside of the Vyper test suite. Eventually, the decoder will be available on mainnet at a fixed address. But for now, here’s how to create RLP decoder on other chains:

1. send 6270960000000000 wei to 0xd2c560282c9C02465C2dAcdEF3E859E730848761

2. Publish this tx to create the contract


3. This is the contract address: 0xCb969cAAad21A78a24083164ffa81604317Ab603

Low Level Built in Functions

Vyper contains a set of built in functions which execute opcodes such as SEND or SELFDESTRUCT.

send(to: address, value: uint256(wei)) → None

Sends 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


The amount to send is always specified in wei.

raw_call(to: address, data: bytes, outsize: int, gas: uint256, value: uint256(wei) = 0, is_delegate_call: bool = False) → bytes[outsize]

Calls to the specified Ethereum address.

  • to: Destination address to call to
  • data: Data to send to the destination address
  • outsize: Maximum length of the bytes array returned from the call
  • gas: Amount of gas to atttach to the call
  • 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)

Returns the data returned by the call as a bytes list, with outsize as the max length.

selfdestruct(to: address) → None

Triggers the SELFDESTRUCT opcode (0xFF), causing the contract to be destroyed.

  • to: Address to forward the contract’s ether balance to


This method will delete the contract from the Ethereum blockchain. All non-ether assets associated with this contract will be “burned” and the contract will be inaccessible.

raise(reason: str) → None

Raises an exception.

  • reason: The exception reason (must be <= 32 bytes)

This method triggers the REVERT opcode (0xFD) with the provided reason given as the error message. The code will stop operation, the contract’s state will be reverted to the state before the transaction took place and the remaining gas will be returned to the transaction’s sender.


To give it a more Python-like syntax, the raise function can be called without parenthesis, the syntax would be raise "An exception". Even though both options will compile, it’s recommended to use the Pythonic version without parentheses.

assert(cond: bool, reason: str = None) → None

Asserts the specified condition.

  • cond: The boolean condition to assert
  • reason: The exception reason (must be <= 32 bytes)

This method’s behavior is equivalent to:

if not cond:
    raise reason

The only difference in behavior is that assert can be called without a reason string, while raise requires one.

If the reason string is set to UNREACHABLE, an INVALID opcode (0xFE) will be used instead of REVERT. In this case, calls that revert will not receive a gas refund.

You cannot directly assert the result of a non-constant function call. The proper pattern for doing so is to assign the result to a memory variable, and then call assert on that variable. Alternatively, use the assert_modifiable method.


To give it a more Python-like syntax, the assert function can be called without parenthesis, the syntax would be assert your_bool_condition. Even though both options will compile, it’s recommended to use the Pythonic version without parenthesis.

assert_modifiable(cond: bool) → None

Asserts a specified condition, without checking for constancy on a callable condition.

  • cond: The boolean condition to assert

Use assert_modifiable in place of assert when you wish to directly assert the result of a potentially state-changing call.

For example, a common use case is verifying the results of an ERC20 token transfer:

def transferTokens(token: address, to: address, amount: uint256) -> bool:
    assert_modifiable(ERC20(token).transfer(to, amount))
    return True
raw_log(topics: bytes32[4], data: bytes) → 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
  • data: Unindexed event data to include in the log

This method provides low-level access to the LOG opcodes (0xA0..``0xA4``). The length of topics determines which opcode will be used.

create_forwarder_to(target: address, value: uint256(wei) = 0) → address

Duplicates a contract’s code and deploys it as a new instance, by means of a DELEGATECALL.

  • target: Address of the contract to duplicate
  • value: The wei value to send to the new contract address (Optional, default 0)

Returns the address of the duplicated contract.

blockhash(block_num: uint256) → bytes32

Returns the hash of the block at the specified height.


The EVM only provides access to the most 256 blocks. This function will return 0 if the block number is greater than or equal to the current block number or more than 256 blocks behind the current block.