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In this post I show you how to call into this from Python which is something that turns out to be almost trivially easy to set up. Python can work well as a kind of overpowered scripting language for automating complicated tasks through the bitcoin reference client, but this is also a great way to get started out if you're interested in writing more involved software that works with bitcoin transactions or the bitcoin blockchain.
Python has good support for byte sequences and large integers and seems to be quite a good fit for bitcoin operations in general, while the reference client has a great deal of test coverage, and deals with some tricky details very robustly. Using the RPC interface means that you can take advantage of reference client code for things like network and peer connectivity, wallet management and signing, whilst still retaining the possibility to get down and dirty with some lower level details such as raw transaction construction.
I'm going to assume you have the bitcoin reference client bitcoind installed and set up and I'm not going to talk about issues such as 'bootstrapping' the client to reduce initial block chain synchonisation times , as there should be plenty of other material available for these topics elsewhere on the web.
See this blog post , for example. This will start bitcoind as both a client which connects to other nodes in the bitcoin network and a local server which you can connect to for RPC calls. Otherwise it will just get straight into the continuous process of connecting to other nodes in the bitcoin network and starting or maintaining synchronisation with the network blockchain, while also listening out for local RPC calls.
Note that you can also run bitcoind as a daemon background process but I prefer to just give the server a dedicated terminal and can then switch to this terminal if I want to see some of the current server output.
It's not all intuitive and obvious, and I recommend starting out with testnet until you're pretty sure about what you're doing, to avoid the possibility of losing real money! You can use the same bitcoind executable to make RPC calls just by adding an RPC method at the end of command line , but this is depreciated, and you're now supposed to use bitcoin-cli for this purpose.
So, with a rpc user setup, and the bitcoin server running in a separate terminal, you should be able to do stuff like:.
When run in server mode, bitcoind sets up an http server, listens out for requests, decodes method name and parameters as JSON data from the http request contents, and encodes the result also as JSON in the http response.
On the other side, bitcoin-cli looks up your rpc connection information in the bitcoin configuration file, makes an http connection to the server, encodes the method name and parameters you specify on the command line as JSON, makes a specially formed http request which includes this data, decodes the resulting JSON data from the http response, and prints this out.
Thanks to the excellent requests library for Python we can do essentially the same thing as bitcoin-cli from within our Python scripts, very easily. A minimal script for querying the same block details as the bitcoin-cli 'getblock' method call above is as follows:. If you get an import error then that means that you need to install the requests library.
I won't go into details for this, but there are plenty of other resources you can refer to for this. And you'll also need to change the rpc user and password to whatever you have in your bitcoin. Note that the data is returned in the form of Python dictionaries and lists, and can be traversed and referenced directly from your Python scripts without any further parsing or processing required.
It's nice to add in a bit of error checking and encapsulate this functionality in a python class. I'm using the following class definition for this:. Note that this puts connections through a Session object, just in case this makes a difference to performance, since, according to the documentation for the requests library , sessions implement automatic keep-alive for connection reuse across requests.
And then there is also some error handling and automatic reconnection. If you ever find yourself doing more complicated operations that involve non-trivial program state then having some kind of automatic reconnect can potentially save a lot of stress trying to recreate program state and complete operations manually!
The params argument is a Python version of variable argument lists, and wraps up all the arguments passed after rpcMethod into a tuple. There are some wrapper libraries around that go on to add actual function stubs for each rpc method e. I think that a stubs layer is just something else that can get out of sync with the actual set of methods available on your RPC server, however. In terms of interface, the above works fine for me, and I like the fact that the RPCHost class is then simple enough to avoid the need to add in another third party dependency.
There are a bunch of other cryptocurrencies that use essentially the same code base as the original bitcoin client reference code. It looks like this includes the RPC setup, and you can then use essentially the same RPC setup with at least some of these 'altcoins'. For litecoin, for example and the litecoind reference client , just change the RPC port to for litecoin testnet, and for litecoin main net.
Copying and pasting your rpc username and password into scripts manually is a bit inconvenient, but we can improve on this by reading these values directly from the bitcoin config file. It seems like the standard way to read config files into Python is with the ConfigParser module, but it turns out that we can't use ConfigParser directly in this case.
The problem is that bitcoin config files loaded by bitcoind with Boost. A bit of googling shows that other people have encountered this problem, in this stackoverflow question for example, but I didn't really like any of the suggested workarounds. Config files are not so complicated, so I chose to just parse these files directly myself, using the following code:.
The config file is expected to be ascii, but we want to handle stuff like utf-8 and unicode characters in comments without falling over. And this should then work on both Python 2 and 3, returning a dictionary with unicode strings in each case. To connect to litecoind change '. Making RPC calls to bitcoind is easy! Next time you find yourself spending time copying and pasting data from the output of one RPC command into the input of another, consider automating this with a Python script..
April 7, , Python and bitcoin Python has good support for byte sequences and large integers and seems to be quite a good fit for bitcoin operations in general, while the reference client has a great deal of test coverage, and deals with some tricky details very robustly. Running the reference client as an RPC server I'm going to assume you have the bitcoin reference client bitcoind installed and set up and I'm not going to talk about issues such as 'bootstrapping' the client to reduce initial block chain synchonisation times , as there should be plenty of other material available for these topics elsewhere on the web.
We'll need to run bitcoind as a server, which I do with the following command: