# Types¶

Vyper is a statically typed language, which means that the type of each variable (state and local) needs to 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
`x not y` Logical negation
`x and y` Logical conjunction
`x or y` Logical disjunction
`x == y` Equality
`x != y` Inequality

The operators `or` and `and` apply the common short-circuiting rules.

### 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.

#### 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` Addition
`x - y` Subtraction
`-x` Unary minus/Negation
`x * y` Multiplication
`x / y` Division
`x**y` Exponentiation
`x % y` Modulo
`min(x, y)` Minimum
`max(x, y)` Maximum

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

### 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).

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.

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

##### Arithmetic Operators¶

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

##### Bitwise Operators¶
Operator Description
`bitwise_and(x, y)` AND
`bitwise_not(x, y)` NOT
`bitwise_or(x, y)` OR
`bitwise_xor(x, y)` XOR
`shift(x, _shift)` Bitwise Shift

`x` and `y` must be of the type `uint256`. `_shift` must be of the type `int128`.

Note

Positive `_shift` equals a left shift; negative `_shift` equals a right shift. Values shifted above/below the most/least significant bit get discarded.

### 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).

#### 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¶

`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. It returns in hexadecimal notation with a leading `0x`.

##### Members¶
Member Description
`balance` Query the balance of an address. Returns `wei_value`.
`codesize` Query the code size of an address. Returns `int128`.

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

### Unit Types¶

Vyper allows the definition of types with discrete units e.g. meters, seconds, wei, … . These types may only be based on either `uint256`, `int128` or `decimal`. Vyper has 3 unit types built in, which are the following:

#### Time¶

Keyword Unit Base type Description
`timestamp` 1 sec `uint256` This represents a point in time.
`timedelta` 1 sec `uint256` This is a number of seconds.

Note

Two `timedelta` can be added together, as can a `timedelta` and a `timestamp`, but not two `timestamps`.

#### Wei¶

Keyword Unit Base type Description
`wei_value` 1 wei `uint256` This is an amount of Ether in wei.

### Custom Unit Types¶

Vyper allows you to add additional not-provided unit label to either `uint256`, `int128` or `decimal`.

Custom units example:

```# specify units used in the contract.
units: {
cm: "centimeter",
km: "kilometer"
}
```

Having defined the units they can be defined on variables as follows.

Custom units usage:

```a: int128(cm)
b: uint256(km)
```

### 32-bit-wide Byte Array¶

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

Example:

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

#### Operators¶

Keyword Description
`len(x)` Return the length as an integer.
`sha3(x)` Return the sha3 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.

### Fixed-size 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.

#### Strings¶

Fixed-size byte arrays can hold strings with equal or fewer characters than the maximum length of the byte array.

Example:

```exampleString = "Test String"
```

#### Operators¶

Keyword Description
`len(x)` Return the length as an integer.
`sha3(x)` Return the sha3 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 while `_start` and `_len` are integers.

## 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.

#### Syntax¶

Lists can be declared with `_name: _ValueType[_Integer]`. Multidimensional lists are also possible.

Example:

```#Defining a list
exampleList: int128[3]
#Setting values
exampleList = [10, 11, 12]
exampleList[2] = 42
#Returning a value
return exampleList[0]
```

### Structs¶

Structs are custom defined types that can group several variables.

#### Syntax¶

Structs can be accessed via `struct.argname`. Example:

```#Defining a struct
exampleStruct: {
value1: int128,
value2: decimal
}
#Accessing a value
exampleStruct.value1 = 1
```

### Mappings¶

Mappings in Vyper can be seen as hash tables which 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 similarity ends here, though: The key data is not actually stored in a mapping, only its `keccak256` hash used to look up the value. Because of this, mappings do not have a length or a concept of a key or value being “set”.

It is possible to mark mappings `public` and have Vyper create a getter. The `_KeyType` will become a required parameter for the getter and it will return `_ValueType`.

Note

Mappings are only allowed as state variables.

#### Syntax¶

Mapping types are declared as `_ValueType[_KeyType]`. Here `_KeyType` can be almost any type except for mappings, a contract, or a struct. `_ValueType` can actually be any type, including mappings.

Example:

```#Defining a mapping
exampleMapping: decimal[int128]
#Accessing a value
exampleMapping[0] = 10.1
```

Note

Mappings can only be accessed, not iterated over.

## Builtin Constants¶

Vyper has a few convenience constants builtin.

Type Name Value
int128 MAX_INT128 2**127 - 1
int128 MIN_INT128 -2**127
decimal MAX_DECIMAL (2**127 - 1)
decimal MIN_DECIMAL (-2**127)
uint256 MAX_UINT256 2**256 - 1

## Custom Constants¶

Custom constants can be defined at a global level in Vyper. To define a constant make use of the constant keyword.

Example:

```TOTAL_SUPPLY: constant(uint256) = 10000000
total_supply: public(uint256)

@public
def __init__():
self.total_supply = TOTAL_SUPPLY
```

```units: {
share: "Share unit"
}

MAX_SHARES: constant(uint256(share)) = 1000
SHARE_PRICE: constant(uint256(wei/share)) = 5

@public
def market_cap() -> uint256(wei):
return MAX_SHARES * SHARE_PRICE
```

## Initial Values and None¶

In Vyper, there is no `null` option like most programing languages have. Thus, every variable type has a default value. Nevertheless Vyper has the option to declare `None` which represent the default value of the type. Note that there is no option to assign `None` when initiating a variable. Also, note that you can’t make comparisons to None. In order to check if a variable is empty, you will need to compare it to its type’s default value.

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

Default Variable Values
Type Default Value
`bool` `False`
`int128` `0`
`uint256` `0`
`decimal` `0.0`
`address` `0x0000000000000000000000000000000000000000`
`bytes32` `'\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00'`

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.