Pyledger¶
A simple ledger for smart contracts written in Python
Smart contracts are taking over the financial ecosystem, but most platforms are terribly complicated given their parallel nature. What happens is that, if you don’t need to deal with parallelism, building a ledger for smart contracts is relatively easy. Here’s where Pyledger comes into play.
Assume that you want to create a smart contract to implement a digital currency system. You have some features you consider necessary, namely creating accounts, adding currency to any account, checking the balance and transfer some amount.
A smart contract is an application, so you need to code to create one. In Pyledger you can implement your smart contract in Python. In a few words, a smart contract in Pyledger is a Python class
from pyledger.server.contract import SimpleContract
class DigitalCurrency(SimpleContract):
accounts = {}
def add_account(self, key: str):
if key in self.accounts:
raise Exception('Account already exists')
self.accounts[key] = 0.0
return key
def increment(self, key: str, quantity: float):
if key not in self.accounts:
raise Exception('Account not found')
self.accounts[key] += quantity
def transfer(self, source: str, dest: str, quantity: float):
if source not in self.accounts:
raise Exception('Source account not found')
if dest not in self.accounts:
raise Exception('Destination account not found')
if self.accounts[source] < quantity:
raise Exception('Not enough funds in source account')
if quantity < 0:
raise Exception('You cannot transfer negative currency')
self.accounts[source] -= quantity
self.accounts[dest] += quantity
def balance(self, key: str):
if key not in self.accounts:
print(self.accounts)
raise Exception('Account not found')
return str(self.accounts[key])
There is no need to deal with the details now, but if you are familiar with Python you more or less understand where the thing is going. Once you have finished creating your smart contract, PyLedger can get it up and running in no time.
from pyledger.server import run
run(DigitalCurrency)
Assume that the previous script is called ledger.py. Running the ledger is as simple as running the script with some options:
$> python ledger.py --sync
Now you have your ledger up and running, you can connect to it with a REPL client:
$> pyledger-shell
Connected to server: tcp:127.0.0.1:9000
Pyledger REPL client, write 'help' for help or 'help command' for help on a specific command
PL >>> help
The Pyledger REPL is a console to interact with a Pyledger server.
The list of available commands is the following
help Shows this help
disconnect Disconnects from the server in a clean way.
contracts Lists the available contracts in the server
api Shows the api for a particular contract
call Calls a method of a contract
broadcast Broadcast message all clients
This client may have some limitations respect to a custom client.
For instance, the server may push notifications to the clients,
and using the client API, you could define callbacks to those
pushed messages.
Read the full documentation in http://pyledger.readthedocs.io
PL >>> contracts
['DigitalCurrency']
PL >>> api DigitalCurrency
{'add_account': {'key': <class 'str'>},
'balance': {'key': <class 'str'>},
'increment': {'key': <class 'str'>, 'quantity': <class 'float'>},
'transfer': {'dest': <class 'str'>,
'quantity': <class 'float'>,
'source': <class 'str'>}}
PL >>> call DigitalCurrency add_account account1
Call with pairs of key value arguments
PL >>> call DigitalCurrency add_account key account1
'account1'
PL >>> call DigitalCurrency increment key account1 quantity 100.0
None
PL >>> call DigitalCurrency balance key account1
'100.0'
PL >>> call DigitalCurrency add_account key account2
'account2'
PL >>> call DigitalCurrency transfer source account1 dest account2 quantity 50.0
None
PL >>> call DigitalCurrency balance key account1
'50.0'
PL >>> call DigitalCurrency balance key account2
'50.0'
PL >>> disconnect
Successfully closed, you can kill this with Ctrl-C
WebSocket connection closed: 1000; None
^CBye
Pyledger is possible thanks to Autobahn
Now that we may have your attention, the actual docs.