# Data Types in neo-python¶

There are a few data types that are good to be familiar with when using neo-python or the NEO blockchain in general. It is useful to have an understanding of these in order to recognize them where they occur in various parts of the system in different formats, and how to work with them. The following section will give a quick overview of each data type and its general usage

Note that these data types are implemented in the neocore project, but used heavily in neo-python.

An address in NEO is actually a public/private key-pair. When you create a wallet, the password you use is used to create a 32 byte private key that is stored and known only to you. This key is paired with a ‘public’ key that is used to identify the address on the network. The only time a private-key is used is when signing a transaction.

If you open the prompt and open a wallet, using the wallet command will output a few things, but one of them is a list of the public keys in your wallet, like:

"public_keys": [
{
"Public Key": "036d4de3e05057df18b82718d635795cb67d9c19001e998d76c77b86081be5f160"
}
],


The Public Key above represents the x and y coordinates on the an ECDSA curve, specifically the SECP256R1 curve, in a compressed format. We derive the Address in a series of steps:

• create a UInt160 or ScriptHash of the public key prepended with 21 and finished with ac

>>> from neocore.Cryptography.Crypto import Crypto
>>> pubkey_hex = '036d4de3e05057df18b82718d635795cb67d9c19001e998d76c77b86081be5f160'
>>> pubkey_hex_for_addr = '21' + pubkey_hex + 'ac'
'21036d4de3e05057df18b82718d635795cb67d9c19001e998d76c77b86081be5f160ac'
>>> script_hash
<neocore.UInt160.UInt160 object at 0x10d33e908>
>>> script_hash.Data
bytearray(b'\x03\x19\xe0)\xb9%\x85w\x90\xe4\x17\x85\xbe\x9c\xce\xc6\xca\xb1\x98\x96')

• second, create an address from this script hash:

>>> addr = Crypto.ToAddress(script_hash)
'AG4GfwjnvydAZodm4xEDivguCtjCFzLcJy'
>>>


If you are interested in the implementation details of the KeyPair, UInt160, or Crypto package, have a look at the neocore repository

## UInt256¶

A UInt256 is used to represent a 32 byte hash. This is normally a hash of a Transaction object or a Block. You will normally see it represented as a 64 character string, or a 66 character string with a 0x hex specifier. Below is a sample of how to interact with a UInt256

>>>
>>> from neocore.UInt256 import UInt256
>>>
>>> hash = "0x99e2be05956027b884cbf11cddbf9d2e5a8fb97ab18d5cde44d5ae2d4c980d18"
>>>
>>> uint = UInt256.ParseString(hash)
>>> uint
<neocore.UInt256.UInt256 object at 0x10cb9b240>
>>> uint.ToString()
'99e2be05956027b884cbf11cddbf9d2e5a8fb97ab18d5cde44d5ae2d4c980d18'
>>> uint.To0xString()
'0x99e2be05956027b884cbf11cddbf9d2e5a8fb97ab18d5cde44d5ae2d4c980d18'
>>> uint.Data
bytearray(b"\x18\r\x98L-\xae\xd5D\xde\\\x8d\xb1z\xb9\x8fZ.\x9d\xbf\xdd\x1c\xf1\xcb\x84\xb8\'\x95\x05\xbe\xe2\x99")
>>>
>>> uint.ToBytes()
b'99e2be05956027b884cbf11cddbf9d2e5a8fb97ab18d5cde44d5ae2d4c980d18'
>>>
>>> data = uint.Data
>>> data
bytearray(b"\x18\r\x98L-\xae\xd5D\xde\\\x8d\xb1z\xb9\x8fZ.\x9d\xbf\xdd\x1c\xf1\xcb\x84\xb8\'\x95\x05\xbe\xe2\x99")
>>>
>>> copy = UInt256(data=data)
>>>
>>> copy.To0xString()
'0x99e2be05956027b884cbf11cddbf9d2e5a8fb97ab18d5cde44d5ae2d4c980d18'
>>>


One thing to note, while we normally see the string, or 0x string version of a UInt256

## UInt160¶

A UInt160 is used to represent a 20 byte hash, and might also be referred to as a ScriptHash. It is used to represent Address objects in NEO, whether they are normal addresses or addresses of Smart Contracts on the network. Below is a sample of how to interact with a UInt160

>>>
>>> data = bytearray(b'\x03\x19\xe0)\xb9%\x85w\x90\xe4\x17\x85\xbe\x9c\xce\xc6\xca\xb1\x98\x96')
>>>
>>> from neocore.UInt160 import UInt160
>>>
>>> new_sh = UInt160(data=data)
>>> new_sh
<neocore.UInt160.UInt160 object at 0x10d3460b8>
>>> new_sh.Data
bytearray(b'\x03\x19\xe0)\xb9%\x85w\x90\xe4\x17\x85\xbe\x9c\xce\xc6\xca\xb1\x98\x96')
>>>
>>> new_sh.To0xString()
'0x9698b1cac6ce9cbe8517e490778525b929e01903'
>>>
>>> sh_again = UInt160.ParseString( new_sh.To0xString() )
>>> sh_again.Data
bytearray(b'\x03\x19\xe0)\xb9%\x85w\x90\xe4\x17\x85\xbe\x9c\xce\xc6\xca\xb1\x98\x96')
>>>
'AG4GfwjnvydAZodm4xEDivguCtjCFzLcJy'
>>>


## Fixed8¶

A Fixed8 is used to represent numbers with 8 decimals in an integer format. Below is a basic example of using a Fixed8:

>>> from neocore.Fixed8 import Fixed8
>>>
>>> three = Fixed8.FromDecimal(3)
>>> three.value
300000000
>>> three.ToInt()
3
>>> three.ToString()
'3.0'
>>>
>>>
>>> point5 = Fixed8(50000000)
>>> point5.ToString()
'0.5'
>>>
>>> point5 + three
<neocore.Fixed8.Fixed8 object at 0x10cd48ba8>
>>> threepoint5 = point5 + three
>>> threepoint5.value
350000000
>>>
>>> threepoint5.ToString()
'3.5'
>>>
>>>
>>> threepoint5 * 2
Traceback (most recent call last):
File "<input>", line 1, in <module>
threepoint5 * 2
File "/Users/thomassaunders/Workshop/neo-python/venv/lib/python3.6/site-packages/neocore/Fixed8.py", line 85, in __mul__
return Fixed8(self.value * other.value)
AttributeError: 'int' object has no attribute 'value'
>>>
>>>


Here are a few thoughts to sum up the above:

• if you want to create a Fixed8 and you have a decimal, the easiest thing to do is to use the Fixed8.FromDecimal method.
• you can do math on Fixed8 objects, assuming each operand is a Fixed8
• doing math between a Fixed8 and another type of number will raise an error
• you can access the full value of a Fixed8 object by accessing the value attribute

## BigInteger¶

A BigInteger is used to store and perform math on arbitrarily sized integers, both negative and positive. The are useful for serializing numbers to bytes and back. Here is some sample usage of a BigInteger

>>> from neocore.BigInteger import BigInteger
>>>
>>> bi = BigInteger(10000)
>>>
>>> bi.ToByteArray()
b"\x10'"
>>>
>>> bi2 = BigInteger.FromBytes( bi.ToByteArray() )
>>> bi2
10000
>>>
>>> bi3 = BigInteger(-3)
>>>
>>> bi4 = bi2 * bi3
>>> bi4
-30000
>>>
>>> bi4 += 100000
>>> bi4
70000
>>> bi4.ToByteArray()
b'p\x11\x01'
>>>


One thing to note with the BigInteger implementation is that it differs a bit from Fixed8 in that you can perform math operations between a BigInteger and a normal integer without problems.

## ContractParameterTypes¶

What follows are the ContractParameterTypes that are used in creating and invoking Smart Contracts

Description:
Contract Parameter Type in neo.Wallets
Usage:
from neo.SmartContract.ContractParameterType import ContractParameterType
class neo.SmartContract.ContractParameterType.ContractParameterType[source]

Contract Parameter Types are used to denote different types of objects used in the VM

Signature

00

Boolean

01

Integer

02

Hash160

03

Hash256

04

ByteArray

05

PublicKey

06

String

07

Array

10

InteropInterface

f0

Void

ff

neo.SmartContract.ContractParameterType.ToName(param_type)[source]

Gets the name of a ContractParameterType based on its value :param param_type: type to get the name of :type param_type: ContractParameterType

Returns: str