fakeredis: A fake version of a redis-py

Intro | How to Use | Contributing | Guides | Sponsoring

Intro

fakeredis is a pure-Python implementation of the redis-py python client that simulates talking to a redis server. This was created for a single purpose: to write tests. Setting up redis is not hard, but many times you want to write tests that do not talk to an external server (such as redis). This module now allows tests to simply use this module as a reasonable substitute for redis.

For a list of supported/unsupported redis commands, see REDIS_COMMANDS.md.

Installation

To install fakeredis-py, simply:

pip install fakeredis        # No additional modules support

pip install fakeredis[lua]   # Support for LUA scripts

pip install fakeredis[json]  # Support for RedisJSON commands

How to Use

FakeRedis can imitate Redis server version 6.x or 7.x. If you do not specify the version, version 7 is used by default.

The intent is for fakeredis to act as though you're talking to a real redis server. It does this by storing state internally. For example:

>>> import fakeredis
>>> r = fakeredis.FakeStrictRedis(version=6)
>>> r.set('foo', 'bar')
True
>>> r.get('foo')
'bar'
>>> r.lpush('bar', 1)
1
>>> r.lpush('bar', 2)
2
>>> r.lrange('bar', 0, -1)
[2, 1]

The state is stored in an instance of FakeServer. If one is not provided at construction, a new instance is automatically created for you, but you can explicitly create one to share state:

>>> import fakeredis
>>> server = fakeredis.FakeServer()
>>> r1 = fakeredis.FakeStrictRedis(server=server)
>>> r1.set('foo', 'bar')
True
>>> r2 = fakeredis.FakeStrictRedis(server=server)
>>> r2.get('foo')
'bar'
>>> r2.set('bar', 'baz')
True
>>> r1.get('bar')
'baz'
>>> r2.get('bar')
'baz'

It is also possible to mock connection errors, so you can effectively test your error handling. Simply set the connected attribute of the server to False after initialization.

>>> import fakeredis
>>> server = fakeredis.FakeServer()
>>> server.connected = False
>>> r = fakeredis.FakeStrictRedis(server=server)
>>> r.set('foo', 'bar')
ConnectionError: FakeRedis is emulating a connection error.
>>> server.connected = True
>>> r.set('foo', 'bar')
True

Fakeredis implements the same interface as redis-py, the popular redis client for python, and models the responses of redis 6.x or 7.x.

Use to test django-rq

There is a need to override django_rq.queues.get_redis_connection with a method returning the same connection.

from fakeredis import FakeRedisConnSingleton

django_rq.queues.get_redis_connection = FakeRedisConnSingleton()

Support for additional modules

RedisJson

Currently, Redis Json module is partially implemented ( see supported commands).

>>> import fakeredis
>>> from redis.commands.json.path import Path
>>> r = fakeredis.FakeStrictRedis()
>>> assert r.json().set("foo", Path.root_path(), {"x": "bar"}, ) == 1
>>> r.json().get("foo")
{'x': 'bar'}
>>> r.json().get("foo", Path("x"))
'bar'

Lua support

If you wish to have Lua scripting support (this includes features like redis.lock.Lock, which are implemented in Lua), you will need lupa, you can simply install it using pip install fakeredis[lua]

JSON support

Support for JSON commands (eg, JSON.GET) is implemented using jsonpath-ng, you can simply install it using pip install fakeredis[json].

Known Limitations

Apart from unimplemented commands, there are a number of cases where fakeredis won't give identical results to real redis. The following are differences that are unlikely to ever be fixed; there are also differences that are fixable (such as commands that do not support all features) which should be filed as bugs in GitHub.

• Hyperloglogs are implemented using sets underneath. This means that the type command will return the wrong answer, you can't use get to retrieve the encoded value, and counts will be slightly different (they will in fact be exact).

• When a command has multiple error conditions, such as operating on a key of the wrong type and an integer argument is not well-formed, the choice of error to return may not match redis.

• The incrbyfloat and hincrbyfloat commands in redis use the C long double type, which typically has more precision than Python's float type.

• Redis makes guarantees about the order in which clients blocked on blocking commands are woken up. Fakeredis does not honour these guarantees.

• Where redis contains bugs, fakeredis generally does not try to provide exact bug-compatibility. It's not practical for fakeredis to try to match the set of bugs in your specific version of redis.

• There are a number of cases where the behaviour of redis is undefined, such as the order of elements returned by set and hash commands. Fakeredis will generally not produce the same results, and in Python versions before 3.6 may produce different results each time the process is re-run.

• SCAN/ZSCAN/HSCAN/SSCAN will not necessarily iterate all items if items are deleted or renamed during iteration. They also won't necessarily iterate in the same chunk sizes or the same order as redis.

• DUMP/RESTORE will not return or expect data in the RDB format. Instead, the pickle module is used to mimic an opaque and non-standard format. WARNING: Do not use RESTORE with untrusted data, as a malicious pickle can execute arbitrary code.

Local development environment

To ensure parity with the real redis, there are a set of integration tests that mirror the unittests. For every unittest that is written, the same test is run against a real redis instance using a real redis-py client instance. In order to run these tests you must have a redis server running on localhost, port 6379 (the default settings). WARNING: the tests will completely wipe your database!

First install poetry if you don't have it, and then install all the dependencies:

pip install poetry
poetry install

To run all the tests:

poetry run pytest -v

If you only want to run tests against fake redis, without a real redis::

poetry run pytest -m fake

Because this module is attempting to provide the same interface as redis-py, the python bindings to redis, a reasonable way to test this to take each unittest and run it against a real redis server. fakeredis and the real redis server should give the same result. To run tests against a real redis instance instead:

poetry run pytest -m real

If redis is not running, and you try to run tests against a real redis server, these tests will have a result of 's' for skipped.

There are some tests that test redis blocking operations that are somewhat slow. If you want to skip these tests during day to day development, they have all been tagged as 'slow' so you can skip them by running:

poetry run pytest -m "not slow"

Contributing

Contributions are welcome. Please see the contributing guide for more details. If you'd like to help out, you can start with any of the issues labeled with Help wanted.

There are guides how to implement a new command and how to write new test cases.

New contribution guides are welcome.

Guides

Implementing support for a command

Creating a new command support should be done in the FakeSocket class (in _fakesocket.py) by creating the method and using @command decorator (which should be the command syntax, you can use existing samples on the file).

For example:

class FakeSocket(BaseFakeSocket, FakeLuaSocket):
    # ...
    @command(name='zscore', fixed=(Key(ZSet), bytes), repeat=(), flags=[])
    def zscore(self, key, member):
        try:
            return self._encodefloat(key.value[member], False)
        except KeyError:
            return None

How to use @command decorator

The @command decorator register the method as a redis command and define the accepted format for it. It will create a Signature instance for the command. Whenever the command is triggered, the Signature.apply(..) method will be triggered to check the validity of syntax and analyze the command arguments.

By default, it takes the name of the method as the command name.

If the method implements a subcommand (eg, SCRIPT LOAD), a Redis module command (eg, JSON.GET), or a python reserve word where you can not use it as the method name (eg, EXEC), then you can supply explicitly the name parameter.

If the command implemented require certain arguments, they can be supplied in the first parameter as a tuple. When receiving the command through the socket, the bytes will be converted to the argument types supplied or remain as bytes.

Argument types (All in _commands.py):

• Key(KeyType) - Will get from the DB the key and validate its value is of KeyType (if KeyType is supplied). It will generate a CommandItem from it which provides access to the database value.
• Int - Decode the bytes to int and vice versa.
• DbIndex/BitOffset/BitValue/Timeout - Basically the same behavior as Int, but with different messages when encode/decode fail.
• Hash - dictionary, usually describe the type of value stored in Key Key(Hash)
• Float - Encode/Decode bytes <-> float
• SortFloat - Similar to Float with different error messages.
• ScoreTest - Argument converter for sorted set score endpoints.
• StringTest - Argument converter for sorted set endpoints (lex).
• ZSet - Sorted Set.

Implement a test for it

There are multiple scenarios for test, with different versions of redis server, redis-py, etc. The tests not only assert the validity of output but runs the same test on a real redis-server and compares the output to the real server output.

• Create tests in the relevant test file.
• If support for the command was introduced in a certain version of redis-py ( see redis-py release notes) you can use the decorator @testtools.run_test_if_redispy_ver on your tests. example:

@testtools.run_test_if_redispy_ver('above', '4.2.0')  # This will run for redis-py 4.2.0 or above.
def test_expire_should_not_expire__when_no_expire_is_set(r):
    r.set('foo', 'bar')
    assert r.get('foo') == b'bar'
    assert r.expire('foo', 1, xx=True) == 0

Updating REDIS_COMMANDS.md

Lastly, run from the root of the project the script to regenerate REDIS_COMMANDS.md:

python scripts/supported.py > REDIS_COMMANDS.md    

Write a new test case

There are multiple scenarios for test, with different versions of python, redis-py and redis server, etc. The tests not only assert the validity of the expected output with FakeRedis but also with a real redis server. That way parity of real Redis and FakeRedis is ensured.

To write a new test case for a command:

• Determine which mixin the command belongs to and the test file for the mixin (eg, string_mixin.py => test_string_commands.py).
• Tests should support python 3.7 and above.
• Determine when support for the command was introduced
  • To limit the redis-server versions it will run on use: @pytest.mark.max_server(version) and @pytest.mark.min_server(version)
  • To limit the redis-py version use @run_test_if_redispy_ver(above/below, version)
• pytest will inject a redis connection to the argument r of the test.

Sample of running a test for redis-py v4.2.0 and above, redis-server 7.0 and above.

@pytest.mark.min_server('7')
@testtools.run_test_if_redispy_ver('above', '4.2.0')
def test_expire_should_not_expire__when_no_expire_is_set(r):
    r.set('foo', 'bar')
    assert r.get('foo') == b'bar'
    assert r.expire('foo', 1, xx=True) == 0

Sponsor

fakeredis-py is developed for free.

You can support this project by becoming a sponsor using this link.

Alternatively, you can buy me coffee using this link: