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 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 

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
do not apply shortcircuiting rules, i.e. both
x and y will always be evaluated.
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.
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 nonnegative integers.
Values¶
Integer values between 0 and (2^{256}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.
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 
uint256_addmod(x, y, z) 
Addition modulo z 
x * y 
Multiplication 
uint256_mulmod(x, y, z) 
Multiplication modulo z 
x / y 
Division 
x**y 
Exponentiation 
x % y 
Modulo 
min(x, y) 
Minimum 
max(x, y) 
Maximum 
x
, y
and z
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 2^{127} and (2^{127}  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¶
Operator  Description 

x + y 
Addition 
x  y 
Subtraction 
x 
Unary minus/Negation 
x * y 
Multiplication 
x / y 
Division 
x % y 
Modulo 
min(x, y) 
Minimum 
max(x, y) 
Maximum 
floor(x) 
Largest integer <= x . Returns int128 . 
ceil(x) 
Smallest integer >= x . Returns int128 . 
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. 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 . 
is_contract 
Query whether it is a contract address. Returns bool . 
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
.
Custom Unit Types¶
Vyper allows you to add additional notprovided 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)
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.
Fixedsize 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
.
Example:
example_bytes: bytes[100] = b"\x01\x02\x03"
Fixedsize 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:
example_str: string[100] = "Test String"
Operators¶
Keyword  Description 

len(x) 
Return the length as an integer. 
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 or string while _start
and _len
are integers.
The len
, keccak256
, concat
, slice
operators can be used with string
and bytes
types.
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.
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
struct MyStruct:
value1: int128
value2: decimal
exampleStruct: MyStruct
#Constructing a struct
exampleStruct = MyStruct({value1: 1, value2: 2})
#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 byterepresentation 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 map(_KeyType, _ValueType)
.
Here _KeyType
can be any base or bytes type. Mappings, contract or structs are not support as key types.
_ValueType
can actually be any type, including mappings.
Example:
#Defining a mapping
exampleMapping: map(int128, decimal)
#Accessing a value
exampleMapping[0] = 10.1
Note
Mappings can only be accessed, not iterated over.
Built In Constants¶
Vyper has a few convenience constants builtin.
Type  Name  Value 

address  ZERO_ADDRESS  0x0000000000000000000000000000000000000000 
bytes32  EMPTY_BYTES32  0x0000000000000000000000000000000000000000000000000000000000000000 
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
Advanced Example:
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¶
In Vyper, there is no null
option like most programming languages have. Thus, every variable type has a default value. In order to check if a variable is empty, you will need to compare it to its type’s default value.
If you would like to reset a variable to its type’s default value, use the builtin clear()
function.
Here you can find a list of all types and default 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.
Type Conversions¶
All type conversions in Vyper must be made explicitly using the builtin convert(a, b)
function. Currently, the following type conversions are supported:
Destination Type (b)  Input Type (a.type)  Allowed Inputs Values (a)  Additional Notes 

bool 
bool 
—  Do not allow converting to/from the same type 
bool 
decimal 
MINNUM...MAXNUM 
Has the effective conversion logic of: return (a != 0.0) 
bool 
int128 
MINNUM...MAXNUM 
Has the effective conversion logic of: return (a != 0) 
bool 
uint256 
0...MAX_UINT256 
Has the effective conversion logic of: return (a != 0) 
bool 
bytes32 
(0x00 * 32)...(0xFF * 32) 
Has the effective conversion logic of: return (a != 0x00) 
bool 
bytes 
(0x00 * 1)...(0xFF * 32) 
Has the effective conversion logic of: return (a != 0x00) 
decimal 
bool 
True / False 
Result will be 0.0 or 1.0 
decimal 
decimal 
—  Do not allow converting to/from the same type 
decimal 
int128 
MINNUM...MAXNUM 

decimal 
uint256 
0...MAXDECIMAL 

decimal 
bytes32 
(0x00 * 32)...(0xFF * 32) 

decimal 
bytes 
(0x00 * 1)...(0xFF * 32) 

int128 
bool 
True / False 
Result will be 0 or 1 
int128 
decimal 
MINNUM...MAXNUM 
Only allow input within int128 supported range, truncates the decimal value 
int128 
int128 
—  Do not allow converting to/from the same type 
int128 
uint256 
0...MAXNUM 

int128 
bytes32 
(0x00 * 32)...(0xFF * 32) 

int128 
bytes 
(0x00 * 1)...(0xFF * 32) 

uint256 
bool 
True / False 
Result will be 0 or 1 
uint256 
decimal 
0...MAXDECIMAL 
Truncates the decimal value 
uint256 
int128 
0...MAXNUM 

uint256 
uint256 
—  Do not allow converting to/from the same type 
uint256 
bytes32 
(0x00 * 32)...(0xFF * 32) 

uint256 
bytes 
(0x00 * 1)...(0xFF * 32) 

bytes32 
bool 
True / False 
Result will be either (0x00 * 32) or (0x00 * 31 + 0x01) 
bytes32 
decimal 
MINDECIMAL...MAXDECIMAL 
Has the effective behavior of multiplying the decimal value by the decimal divisor 10000000000 and then converting that signed integer value to a bytes32 byte array 
bytes32 
int128 
MINNUM...MAXNUM 

bytes32 
uint256 
0...MAX_UINT256 

bytes32 
bytes32 
—  Do not allow converting to/from the same type 
bytes32 
bytes 
(0x00 * 1)...(0xFF * 32) 
Leftpad input bytes to size of 32 