factom-api 1.0.3
Python client library for the Factom API
License: MIT License

factom-api
==========

This library provides Python clients for interacting with the factomd
and factom-walletd APIs. While not all API methods have been implemented
yet, you'll find most of what you need to build a working application
are available, along with shortcut methods for accomplishing common
tasks involving multiple calls between the wallet and daemon.

Because Python 2 is reaching EOL, this API client (from version 1.0.0
onwards) targets Python 3.5 and higher.

If you're unfamiliar with Factom, I encourage you to `read the
documentation <http://docs.factom.com/>`__, especially the `white
paper <https://github.com/FactomProject/FactomDocs/blob/master/whitepaper.md>`__.
In a nutshell, Factom provides a layer on top of the Bitcoin blockchain
making it possible to secure data faster and in larger amounts than the
Bitcoin network would allow alone.

Getting started
---------------

Installing the API client
~~~~~~~~~~~~~~~~~~~~~~~~~

The easiest way to install is directly from pip:

::

    $ pip install factom-api

Usage
-----

I'll go over a few common operations here you'll most likely use in
applications. In general you'll need instances of both the wallet and
factomd clients to build and submit transactions. To build new clients:

.. code:: python

    from factom import Factomd, FactomWalletd

    # Default settings
    factomd = Factomd()
    walletd = FactomWalletd()

    # You can also specify default fct and ec addresses, change host, or specify RPC credentials, for example:
    fct_address = 'FA2jK2HcLnRdS94dEcU27rF3meoJfpUcZPSinpb7AwQvPRY6RL1Q'
    ec_address = 'EC2jhmCtabeTXGtuLi3AaPzvwSuqksdVsjfxXMXV5gPmipXc4GjC'

    factomd = Factomd(
        host='http://someotherhost:8088',
        fct_address=fct_address,
        ec_address=ec_address,
        username='rpc_username',
        password='rpc_password'
    )

Transacting factoids to factoids
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

First let's query the balance in both of our fct addresses:

.. code:: python

    >>> fct_address1 = 'FA2jK2HcLnRdS94dEcU27rF3meoJfpUcZPSinpb7AwQvPRY6RL1Q'
    >>> fct_address2 = 'FA3TMQHrCrmLa4F9t442U3Ab3R9sM1gThYMDoygPEVtxrbHtFRtg'
    >>> ec_address = 'EC2jhmCtabeTXGtuLi3AaPzvwSuqksdVsjfxXMXV5gPmipXc4GjC'

    # Initialize the two clients
    >>> factomd = Factomd()
    >>> walletd = FactomWalletd()

    # Query the balance in our first address. There should be a large amount
    >>> factomd.factoid_balance(fct_address1)
    {'balance': 1999999735950}

    # The second address should be empty.
    >>> factomd.factoid_balance(fct_address2)
    {'balance': 0}

The wallet client provides a shorcut method ``fct_to_fct()`` which
performs all the API calls needed to submit a simple fct to fct
transaction. This includes adding inputs and outputs, calculating the
fee, building the signed transaction, and submitting it to the network.

.. code:: python

    >>> walletd.fct_to_fct(factomd, 50000, fct_to=fct_address2, fct_from=fct_address1)
    {'message': 'Successfully submitted the transaction', 'txid': 'a4d641f13d82b1d1682549d44fa41c7e1b01f1a16f8cbddb5c695df53fcebfd7'}

The server reports the transaction was submitted and if we wait a few
seconds we can see the results:

.. code:: python

    >>> factomd.factoid_balance(fct_address2)
    {'balance': 50000}

Converting factoids to entry credits
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Our new entry credit address should have a balance of zero:

.. code:: python

    >>> factomd.entry_credit_balance(ec_address)
    {'balance': 0}

First, we need to ask for the conversion rate:

.. code:: python

    >>> factomd.entry_credit_rate()
    {'rate': 1000}

This tells us we'll need to burn 1000 factoids in exchange for 1 entry
credit, so let's purchase 50 entry credits for 50000 factoids. Similar
to ``fct_to_fct()``, the wallet client also provides a ``fct_to_ec()``
shortcut for building and submitting simple fct conversion transactions.

.. code:: python

    >>> walletd.fct_to_ec(factomd, 50000, fct_address=fct_address1, ec_address=ec_address)
    {'message': 'Successfully submitted the transaction', 'txid': 'd70b14ce05a21dbf772d1894383694b4537e17454915fc42dc20f02c1e0e2df2'}

And if we query our entry credit balance we see the conversion has
happened:

.. code:: python

    >>> factomd.entry_credit_balance(ec_address)
    {'balance': 50}

Writing chains and entries
~~~~~~~~~~~~~~~~~~~~~~~~~~

The real meat and potatoes is the ability to easily read from and write
data to the blockchain. Let's write some test data. The wallet client
provides a ``new_chain()`` shortcut method that handles the API calls
and encoding needed for creating a new chain. You could also build the
transaction manually if you'd like more control over each step, but for
most cases this is going to be easier.

.. code:: python

    >>> walletd.new_chain(factomd, ['random', 'chain', 'id'], 'chain_content', ec_address=ec_address)
    {'message': 'Entry Reveal Success', 'entryhash': 'f9662a4675f4bb6566337eafd8237ab9fd2ba396947dadeb677c0526d367a5ce', 'chainid': 'da2ffed0ae7b33acc718089edc0f1d001289857cc27a49b6bc4dd22fac971495'}

If we wait a few minutes and search for the chain ID in the explorer we
can see our initial entry:

.. figure:: screenshots/chain.png
   :alt: Our new chain

   Our new chain

Now let's add another entry to the same chain:

.. code:: python

    >>> chain_id = 'da2ffed0ae7b33acc718089edc0f1d001289857cc27a49b6bc4dd22fac971495'
    >>> walletd.new_entry(factomd, chain_id, ['random', 'entry', 'id'], 'entry_content', ec_address=ec_address)
    {'message': 'Entry Reveal Success', 'entryhash': '96f0472c9ec8a76c861fb4df37beb742938f41bbe492dc04893337bf387b83c5', 'chainid': 'da2ffed0ae7b33acc718089edc0f1d001289857cc27a49b6bc4dd22fac971495'}

You should see the new entry appear shortly.

Reading entries
~~~~~~~~~~~~~~~

If the entries in your chain reference each other, you may want to scan
the entire chain in order to verify its integrity. The factomd client
provides a ``read_chain()`` method which iterates over all
entry-containing blocks and returns a list of entries in reverse order.

.. code:: python

    >>> chain_id = 'da2ffed0ae7b33acc718089edc0f1d001289857cc27a49b6bc4dd22fac971495'
    >>> factomd.read_chain(chain_id)
    [{'chainid': 'da2ffed0ae7b33acc718089edc0f1d001289857cc27a49b6bc4dd22fac971495', 'extids': ['random', 'entry', 'id'], 'content': 'entry_content'}, {'chainid': 'da2ffed0ae7b33acc718089edc0f1d001289857cc27a49b6bc4dd22fac971495', 'extids': ['random', 'chain', 'id'], 'content': 'chain_content'}]

You can see the two entries we created earlier.

Error handling
~~~~~~~~~~~~~~

When things go badly, API methods will raise a
``factom.exceptions.FactomAPIError`` with details about the error.

.. code:: python

    >>> walletd.new_chain(factomd, ['random', 'chain', 'id'], 'chain_content', ec_address=ec_address)
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
      File "/src/factom/client.py", line 196, in new_chain
        'ecpub': ec_address or self.ec_address
      File "/src/factom/client.py", line 56, in _request
        handle_error_response(resp)
      File "/src/factom/exceptions.py", line 18, in handle_error_response
        raise codes[code](message=message, code=code, data=data, response=resp)
    factom.exceptions.InvalidParams: -32602: Invalid params

More data about the error is attached to the exception instance:

.. code:: python

    >>> try:
    ...     walletd.new_chain(factomd, ['random', 'chain', 'id'], 'chain_content', ec_address=ec_address)
    ... except FactomAPIError as e:
    ...     print(e.data)
    ... 
    Chain da2ffed0ae7b33acc718089edc0f1d001289857cc27a49b6bc4dd22fac971495 already exists

If you'd like to catch more specific errors, there are exception
subclasses for the different error codes returned by the APIs. See
`factom/exceptions.py <factom/exceptions.py>`__ for a list.