Introduction to Chains¶
Introduction¶
Populus has the ability to run and/or connect to a variety of blockchains for you, both programatically and from the command line.
Transient Chains¶
Populus can run two types of transient chains.
tester
A test EVM backed blockchain.
testrpc
Runs the
eth-testrpc
chain which implements the full JSON-RPC interface backed by a test EVM.temp
Runs a blockchain backed by the go-ethereum
geth
client. This chain will use a temporary directory for it’s chain data which will be cleaned up and removed when the chain shuts down.
Local Chains¶
Local chains can be setup within your populus.json
file. Each local chain
stores its chain data in the populus.Project.blockchains_dir
and persists it’s data between runs.
Local chains are backed by the go-ethereum geth
client.
Public Chains¶
Populus can run both the main and ropsten public chains.
mainnet
With
$ populus chain run mainnet
populus will run the the go-ethereum client for you connected to the main public ethereum network.ropsten
With
$ populus chain run ropsten
populus will run the the go-ethereum client for you connected to the ropsten testnet public ethereum network.
Running from the command line¶
The $ populus chain
command handles running chains from the command line.
$ populus chain
Usage: populus chain [OPTIONS] COMMAND [ARGS]...
Manage and run ethereum blockchains.
Options:
-h, --help Show this message and exit.
Commands:
reset Reset a chain removing all chain data and...
run Run the named chain.
Running programatically from code¶
The populus.Project.get_chain(chain_name, chain_config=None)
method returns
a populus.chain.Chain
instance that can be used within your code to run any
populus chain. Also read up on the Web3.py library, which offers additional
functions to communicate with an Ethereum blockchain.
Lets look at a basic example of using the temp
chain.
>>> from populus import Project
>>> project = Project()
>>> with project.get_chain('temp') as chain:
... print('coinbase:', chain.web3.eth.coinbase)
...
...
coinbase: 0x16e11a86ca5cc6e3e819efee610aa77d78d6e075
>>>
>>> with project.get_chain('temp') as chain:
... print('coinbase:', chain.web3.eth.coinbase)
...
...
coinbase: 0x64e49c86c5ad1dd047614736a290315d415ef28e
You can see that each time a temp
chain is instantiated it creates a new
data directory and generates new keys.
The testrpc
chain operates in a similar manner in that each time you run
the chain the EVM data is fully reset. The benefit of the testrpc
server
is that it starts quicker, and has mechanisms for manually resetting the chain.
Here is an example of running the tester
blockchain.
>>> from populus import Project
>>> project = Project()
>>> with project.get_chain('tester') as chain:
... print('coinbase:', chain.web3.eth.coinbase)
... print('blockNumber:', chain.web3.eth.blockNumber)
... chain.mine()
... print('blockNumber:', chain.web3.eth.blockNumber)
... snapshot_id = chain.snapshot()
... print('Snapshot:', snapshot_id)
... chain.mine()
... chain.mine()
... print('blockNumber:', chain.web3.eth.blockNumber)
... chain.revert(snapshot_id)
... print('blockNumber:', chain.web3.eth.blockNumber)
...
coinbase: 0x82a978b3f5962a5b0957d9ee9eef472ee55b42f1
blockNumber: 1
blockNumber: 2
Snapshot: 0
blockNumber: 4
blockNumber: 2
Note
The testrpc
chain can be run in the same manner.