# Types¶

Vyper is a statically typed language. The type of each variable (state and local) must be specified or at least known at compile-time. Vyper provides several elementary types which can be combined to form complex types.

In addition, types can interact with each other in expressions containing operators.

## Value Types¶

The following types are also called value types because variables of these types will always be passed by value, i.e. they are always copied when they are used as function arguments or in assignments.

### Boolean¶

Keyword: `bool`

A boolean is a type to store a logical/truth value.

#### Values¶

The only possible values are the constants `True` and `False`.

#### Operators¶

Operator

Description

`not x`

Logical negation

`x and y`

Logical conjunction

`x or y`

Logical disjunction

`x == y`

Equality

`x != y`

Inequality

Short-circuiting of boolean operators (`or` and `and`) is consistent with the behavior of Python.

### Signed Integer (256 bit)¶

Keyword: `int256`

A signed integer (256 bit) is a type to store positive and negative integers.

#### Values¶

Signed integer values between -2255 and (2255 - 1), inclusive.

Interger literals cannot have a decimal point even if the decimal value is zero. For example, `2.0` cannot be interpreted as an integer.

#### Operators¶

##### Comparisons¶

Comparisons return a boolean value.

Operator

Description

`x < y`

Less than

`x <= y`

Less than or equal to

`x == y`

Equals

`x != y`

Does not equal

`x >= y`

Greater than or equal to

`x > y`

Greater than

`x` and `y` must be of the type `int256`.

##### Arithmetic Operators¶

Operator

Description

`x + y`

`x - y`

Subtraction

`-x`

Unary minus/Negation

`x * y`

Multiplication

`x / y`

Division

`x**y`

Exponentiation

`x % y`

Modulo

`x` and `y` must be of the type `int256`.

### Signed Integer (128 bit)¶

Keyword: `int128`

A signed integer (128 bit) is a type to store positive and negative integers.

#### Values¶

Signed integer values between -2127 and (2127 - 1), inclusive.

Interger literals cannot have a decimal point even if the decimal value is zero. For example, `2.0` cannot be interpreted as an integer.

#### Operators¶

##### Comparisons¶

Comparisons return a boolean value.

Operator

Description

`x < y`

Less than

`x <= y`

Less than or equal to

`x == y`

Equals

`x != y`

Does not equal

`x >= y`

Greater than or equal to

`x > y`

Greater than

`x` and `y` must be of the type `int128`.

##### Arithmetic Operators¶

Operator

Description

`x + y`

`x - y`

Subtraction

`-x`

Unary minus/Negation

`x * y`

Multiplication

`x / y`

Division

`x**y`

Exponentiation

`x % y`

Modulo

`x` and `y` must be of the type `int128`.

### Unsigned Integer (8 bit)¶

Keyword: `uint8`

An unsigned integer (8 bit) is a type to store non-negative integers.

#### Values¶

Integer values between 0 and (28-1).

Interger literals cannot have a decimal point even if the decimal value is zero. For example, `2.0` cannot be interpreted as an integer.

Note

Integer literals are interpreted as `int128` by default. In cases where `uint8` is more appropriate, such as assignment, the literal might be interpreted as `uint8`. Example: `_variable: uint8 = _literal`. In order to explicitly cast a literal to a `uint8` use `convert(_literal, uint8)`.

#### Operators¶

##### Comparisons¶

Comparisons return a boolean value.

Operator

Description

`x < y`

Less than

`x <= y`

Less than or equal to

`x == y`

Equals

`x != y`

Does not equal

`x >= y`

Greater than or equal to

`x > y`

Greater than

`x` and `y` must be of the type `uint8`.

##### Arithmetic Operators¶

Operator

Description

`x + y`

`x - y`

Subtraction

`x * y`

Multiplication

`x / y`

Division

`x**y`

Exponentiation

`x % y`

Modulo

`x` and `y` must be of the type `uint8`.

### Unsigned Integer (256 bit)¶

Keyword: `uint256`

An unsigned integer (256 bit) is a type to store non-negative integers.

#### Values¶

Integer values between 0 and (2256-1).

Interger literals cannot have a decimal point even if the decimal value is zero. For example, `2.0` cannot be interpreted as an integer.

Note

Integer literals are interpreted as `int128` by default. In cases where `uint256` is more appropriate, such as assignment, the literal might be interpreted as `uint256`. Example: `_variable: uint256 = _literal`. In order to explicitly cast a literal to a `uint256` use `convert(_literal, uint256)`.

#### Operators¶

##### Comparisons¶

Comparisons return a boolean value.

Operator

Description

`x < y`

Less than

`x <= y`

Less than or equal to

`x == y`

Equals

`x != y`

Does not equal

`x >= y`

Greater than or equal to

`x > y`

Greater than

`x` and `y` must be of the type `uint256`.

##### Arithmetic Operators¶

Operator

Description

`x + y`

`x - y`

Subtraction

`x * y`

Multiplication

`x / y`

Division

`x**y`

Exponentiation

`x % y`

Modulo

`x`, `y` and `z` must be of the type `uint256`.

### Decimals¶

Keyword: `decimal`

A decimal is a type to store a decimal fixed point value.

#### Values¶

A value with a precision of 10 decimal places between -2127 and (2127 - 1).

In order for a literal to be interpreted as `decimal` it must include a decimal point.

#### Operators¶

##### Comparisons¶

Comparisons return a boolean value.

Operator

Description

`x < y`

Less than

`x <= y`

Less or equal

`x == y`

Equals

`x != y`

Does not equal

`x >= y`

Greater or equal

`x > y`

Greater than

`x` and `y` must be of the type `decimal`.

##### Arithmetic Operators¶

Operator

Description

`x + y`

`x - y`

Subtraction

`-x`

Unary minus/Negation

`x * y`

Multiplication

`x / y`

Division

`x % y`

Modulo

`x` and `y` must be of the type `decimal`.

Keyword: `address`

#### Values¶

An address type can hold an Ethereum address which equates to 20 bytes or 160 bits. Address literals must be written in hexadecimal notation with a leading `0x` and must be checksummed.

##### Members¶

Member

Type

Description

`balance`

`uint256`

`codehash`

`bytes32`

Keccak of code at an address, `EMPTY_BYTES32` if no contract is deployed

`codesize`

`uint256`

Size of code deployed an address, in bytes

`is_contract`

`bool`

Boolean indicating if a contract is deployed at an address

Syntax as follows: `_address.<member>`, where `_address` is of the type `address` and `<member>` is one of the above keywords.

Note

Operations such as `SELFDESTRUCT` and `CREATE2` allow for the removal and replacement of bytecode at an address. You should never assume that values of address members will not change in the future.

### 32-bit-wide Byte Array¶

Keyword: `bytes32` This is a 32-bit-wide byte array that is otherwise similar to byte arrays.

Example:

```# Declaration
hash: bytes32
# Assignment
self.hash = _hash
```

#### Operators¶

Keyword

Description

`keccak256(x)`

Return the keccak256 hash as bytes32.

`concat(x, ...)`

Concatenate multiple inputs.

`slice(x, start=_start, len=_len)`

Return a slice of `_len` starting at `_start`.

Where `x` is a byte array and `_start` as well as `_len` are integer values.

### Byte Arrays¶

Keyword: `Bytes`

A byte array with a fixed size.

The syntax being `Bytes[maxLen]`, where `maxLen` is an integer which denotes the maximum number of bytes. On the ABI level the Fixed-size bytes array is annotated as `bytes`.

Bytes literals may be given as bytes strings, hexadecimal, or binary.

```bytes_string: Bytes[100] = b"\x01"
hex_bytes: Bytes[100] = 0x01
binary_bytes: Bytes[100] = 0b00000001
```

### Strings¶

Keyword: `String`

Fixed-size strings can hold strings with equal or fewer characters than the maximum length of the string. On the ABI level the Fixed-size bytes array is annotated as `string`.

```example_str: String[100] = "Test String"
```

## Reference Types¶

Reference types do not fit into 32 bytes. Because of this, copying their value is not as feasible as with value types. Therefore only the location, i.e. the reference, of the data is passed.

### Fixed-size Lists¶

Fixed-size lists hold a finite number of elements which belong to a specified type.

Lists can be declared with `_name: _ValueType[_Integer]`.

```# Defining a list
exampleList: int128[3]

# Setting values
exampleList = [10, 11, 12]
exampleList[2] = 42

# Returning a value
return exampleList[0]
```

Multidimensional lists are also possible. The notation for the declaration is reversed compared to some other languages, but the access notation is not reversed.

A two dimensional list can be declared with `_name: _ValueType[inner_size][outer_size]`. Elements can be accessed with `_name[outer_index][inner_index]`.

```# Defining a list with 2 rows and 5 columns and set all values to 0
exampleList2D: int128[5][2] = empty(int128[5][2])

# Setting a value for row the first row (0) and last column (4)
exampleList2D[0][4] = 42

# Setting values
exampleList2D = [[10, 11, 12, 13, 14], [16, 17, 18, 19, 20]]

# Returning the value in row 0 column 4 (in this case 14)
return exampleList2D[0][4]
```

### Structs¶

Structs are custom defined types that can group several variables.

Struct types can be used inside mappings and arrays. Structs can contain arrays and other structs, but not mappings.

Struct members can be accessed via `struct.argname`.

```# Defining a struct
struct MyStruct:
value1: int128
value2: decimal

# Declaring a struct variable
exampleStruct: MyStruct = MyStruct({value1: 1, value2: 2.0})

# Accessing a value
exampleStruct.value1 = 1
```

### Mappings¶

Mappings are hash tables that are virtually initialized such that every possible key exists and is mapped to a value whose byte-representation is all zeros: a type’s default value.

The key data is not stored in a mapping, instead its `keccak256` hash used to look up a value. For this reason mappings do not have a length or a concept of a key or value being “set”.

Mapping types are declared as `HashMap[_KeyType, _ValueType]`.

• `_KeyType` can be any base or bytes type. Mappings, interfaces or structs are not support as key types.

• `_ValueType` can actually be any type, including mappings.

Note

Mappings are only allowed as state variables.

```# Defining a mapping
exampleMapping: HashMap[int128, decimal]

# Accessing a value
exampleMapping[0] = 10.1
```

Note

Mappings have no concept of length and so cannot be iterated over.

## Initial Values¶

Unlike most programming languages, Vyper does not have a concept of `null`. Instead, every variable type has a default value. To check if a variable is empty, you must compare it to the default value for it’s given type.

To reset a variable to it’s default value, assign to it the built-in `empty()` function which constructs a zero value for that type.

Note

Memory variables must be assigned a value at the time they are declared.

Here you can find a list of all types and default values:

Type

Default Value

`address`

`0x0000000000000000000000000000000000000000`

`bool`

`False`

`bytes32`

`0x0000000000000000000000000000000000000000000000000000000000000000`

`decimal`

`0.0`

`int128`

`0`

`uint256`

`0`

Note

In `Bytes` the array starts with the bytes all set to `'\x00'`

Note

In reference types all the type’s members are set to their initial values.

## Type Conversions¶

All type conversions in Vyper must be made explicitly using the built-in `convert(a: atype, btype)` function. Currently, the following type conversions are supported:

In (`atype`)

Out (`btype`)

Allowable Values

`bool`

`decimal`

All

`0.0` or `1.0`

`bool`

`int128`

All

`0` or `1`

`bool`

`uint256`

All

`0` or `1`

`bool`

`bytes32`

All

`0x00` or `0x01`

`bool`

`Bytes`

All

`decimal`

`bool`

All

Returns `a != 0.0`

`decimal`

`int128`

All

Value is truncated

`decimal`

`uint256`

`a >= 0.0`

Value is truncated

`decimal`

`bytes32`

All

`decimal`

`Bytes`

All

`int128`

`bool`

All

Returns `a != 0`

`int128`

`decimal`

All

`int128`

`uint256`

`a >= 0`

Cannot convert negative values

`int128`

`bytes32`

All

`int128`

`Bytes`

All

`uint8`

`bool`

All

Returns `a != 0`

`uint8`

`decimal`

All

`uint8`

`int128`

All

`uint8`

`bytes32`

All

`uint8`

`Bytes`

All

`uint256`

`bool`

All

Returns `a != 0`

`uint256`

`decimal`

`a <= MAX_DECIMAL`

`uint256`

`int128`

`a <= MAX_INT128`

`uint256`

`bytes32`

All

`uint256`

`Bytes`

All

`bytes32`

`bool`

All

`True` if `a` is not empty

`bytes32`

`decimal`

All

`bytes32`

`int128`

All

`bytes32`

`uint256`

All

`bytes32`

`Bytes`

All