Types¶
Vyper is a statically typed language. The type of each variable (state and local) must be specified or at least known at compiletime. 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 
Shortcircuiting of boolean operators (or
and and
) is consistent with
the behavior of Python.
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 2^{127} and (2^{127}  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 
Addition 
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 (256 bit)¶
Keyword: uint256
An unsigned integer (256 bit) is a type to store nonnegative integers.
Values¶
Integer values between 0 and (2^{256}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 
Addition 
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 2^{127} and (2^{127}  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 
Addition 
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
.
Address¶
Keyword: address
The address type holds an Ethereum 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 
Balance of an address 
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.
32bitwide Byte Array¶
Keyword: bytes32
This is a 32bitwide 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 Fixedsize 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
Fixedsize strings can hold strings with equal or fewer characters than the maximum length of the string.
On the ABI level the Fixedsize 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.
Fixedsize Lists¶
Fixedsize lists hold a finite number of elements which belong to a specified type.
Lists can be declared with _name: _ValueType[_Integer]
. Multidimensional lists are also possible.
# 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.
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
.
Mappings¶
Mappings are hash tables that are virtually initialized such that every possible key exists and is mapped to a value whose byterepresentation 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 builtin 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 
1 
uint256 
1 
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 builtin convert(a: atype, btype)
function. Currently, the following type conversions are supported:
In (atype ) 
Out (btype ) 
Allowable Values  Additional Notes 

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  
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 