GraphQL base implementation for Python
Python
Latest commit 9202021 Jul 27, 2018

README.md

GraphQL-core

GraphQL for Python.

This library is a port of graphql-js to Python and currently is up-to-date with release 0.6.0.

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See more complete documentation at http://graphql.org/ and http://graphql.org/docs/api-reference-graphql/.

For questions, ask Stack Overflow.

Getting Started

An overview of the GraphQL language is available in the README for the Specification for GraphQL.

The overview describes a simple set of GraphQL examples that exist as tests in this repository. A good way to get started is to walk through that README and the corresponding tests in parallel.

Using graphql-core

Install from pip:

pip install graphql-core

GraphQL.js provides two important capabilities: building a type schema, and serving queries against that type schema.

First, build a GraphQL type schema which maps to your code base.

from graphql import (
    graphql,
    GraphQLSchema,
    GraphQLObjectType,
    GraphQLField,
    GraphQLString
)

schema = GraphQLSchema(
  query= GraphQLObjectType(
    name='RootQueryType',
    fields={
      'hello': GraphQLField(
        type= GraphQLString,
        resolver=lambda *_: 'world'
      )
    }
  )
)

This defines a simple schema with one type and one field, that resolves to a fixed value. The resolve function can return a value, a promise, or an array of promises. A more complex example is included in the top level tests directory.

Then, serve the result of a query against that type schema.

query = '{ hello }'

result = graphql(schema, query)

# Prints
# {'hello': 'world'} (as OrderedDict)

print result.data

This runs a query fetching the one field defined. The graphql function will first ensure the query is syntactically and semantically valid before executing it, reporting errors otherwise.

query = '{ boyhowdy }'

result = graphql(schema, query)

# Prints
# [GraphQLError('Cannot query field "boyhowdy" on type "RootQueryType".',)]

print result.errors

Executors

The graphql query is executed, by default, synchronously (using SyncExecutor). However the following executors are available if we want to resolve our fields in parallel:

  • graphql.execution.executors.asyncio.AsyncioExecutor: This executor executes the resolvers in the Python asyncio event loop.
  • graphql.execution.executors.gevent.GeventExecutor: This executor executes the resolvers in the Gevent event loop.
  • graphql.execution.executors.process.ProcessExecutor: This executor executes each resolver as a process.
  • graphql.execution.executors.thread.ThreadExecutor: This executor executes each resolver in a Thread.
  • graphql.execution.executors.sync.SyncExecutor: This executor executes each resolver synchronusly (default).

Usage

You can specify the executor to use via the executor keyword argument in the grapqhl.execution.execute function.

from graphql.execution.execute import execute

execute(schema, ast, executor=SyncExecutor())

Contributing

After cloning this repo, create a virtualenv and ensure dependencies are installed by running:

virtualenv venv
source venv/bin/activate
pip install -e ".[test]"

Well-written tests and maintaining good test coverage is important to this project. While developing, run new and existing tests with:

py.test PATH/TO/MY/DIR/test_test.py # Single file
py.test PATH/TO/MY/DIR/ # All tests in directory

Add the -s flag if you have introduced breakpoints into the code for debugging. Add the -v ("verbose") flag to get more detailed test output. For even more detailed output, use -vv. Check out the pytest documentation for more options and test running controls.

GraphQL-core supports several versions of Python. To make sure that changes do not break compatibility with any of those versions, we use tox to create virtualenvs for each python version and run tests with that version. To run against all python versions defined in the tox.ini config file, just run:

tox

If you wish to run against a specific version defined in the tox.ini file:

tox -e py36

Tox can only use whatever versions of python are installed on your system. When you create a pull request, Travis will also be running the same tests and report the results, so there is no need for potential contributors to try to install every single version of python on their own system ahead of time. We appreciate opening issues and pull requests to make GraphQL-core even more stable & useful!

Main Contributors

License

MIT License