redipy 0.2.0

redipy is a uniform interface to Redis-like storage systems. It allows you to use the same Redis API with different backends that implement the same functionality.

redipy

redipy is a Python library that provides a uniform interface to Redis-like storage systems. It allows you to use the same Redis API with different backends that implement the same functionality, such as:

• redipy.memory: A backend that runs inside the current process and stores data in memory using Python data structures.
• redipy.redis: A backend that connects to an actual Redis instance and delegates all operations to it.

Warning

This library is still early in development and not all redis functions are available yet! If you need certain functionality have a look at the contributing section. It is easy to add redis functions to the API.

Installation

You can install redipy using pip:

pip install redipy

Usage

To use redipy, you need to import the library and create a redipy client object with the desired backend. For example:

# Import the redipy library
import redipy

# Create a redipy client using the memory backend
r = redipy.Redis(backend="memory")

# Create a redipy client using the redis backend
r = redipy.Redis(backend="redis", host="localhost", port=6379)

# Or
r = redipy.Redis(
    backend="redis",
    cfg={
        "host": "localhost",
        "port": 6379,
        "passwd": "",
        "prefix": "",
        "path": ".",
    })

The redipy client object supports similar methods and attributes to the official redis Python client library. You can use them as you would normally do with redis. For example:

# Set some values
r.set("foo", "bar")
r.set("baz", "qux")

# Get some values
r.get("foo")  # "bar"
r.get("baz")  # "qux"

# Push some values
r.lpush("mylist", "a", "b", "c")
r.rpush("mylist", "d")

# Pop values
r.lpop("mylist")  # "c"
r.rpop("mylist", 3)  # ["d", "a", "b"]

Features

The main features of redipy are:

• Flexibility: You can choose from different backends that suit your needs and preferences, without changing your code or learning new APIs.

• Performance: You can leverage the high performance of Redis or other backends that offer fast and scalable data storage and retrieval.

• Compatibility: You can use any Redis client or tool with any backend.

• Migration: You can easily migrate data between different backends, or use multiple backends simultaneously.

• Scripting: You can create backend independent redis scripts without using lua. Scripts are written using a symbolic API in python.

Scripts

Redis scripts can be defined via a symbolic API in python and can be executed by any backend:

ctx = redipy.script.FnContext()
cmp = ctx.add_arg("cmp")
inp = redipy.script.RedisList(ctx.add_key("inp"))
left = redipy.script.RedisList(ctx.add_key("left"))
right = redipy.script.RedisList(ctx.add_key("right"))

cur = ctx.add_local(inp.lpop())
# we consume "inp" until it is empty
loop = ctx.while_(cur.ne_(None))
b_then, b_else = loop.if_(redipy.script.ToNum(cur).lt_(cmp))
b_then.add(left.rpush(cur))
b_else.add(right.rpush(cur))
loop.add(cur.assign(inp.lpop()))

ctx.set_return_value(None)

# make sure to build the script only once and reuse the filter_list function
filter_list = r.register_script(ctx)

r.rpush("mylist", "1", "3", "2", "4")
filter_list(
    keys={
        "inp": "mylist",
        "left": "small",
        "right": "big",
    },
    args={
        "cmp": 3,
    })

r.lpop("mylist", 4)  # []
r.lpop("small", 4)  # ["1", "2"]
r.lpop("big", 4)  # ["3", "4"]

Limitations

The current limitations of redipy are:

• Not all Redis commands are supported yet: This will eventually be resolved.
• The API differs slightly: Most notably stoerd values are always strings (i.e., the bytes returned by redis are decoded as utf-8).
• The semantic of redis functions inside scripts has been altered to feel more natural coming from python: Redis functions inside lua scripts often differ greatly from the documented behavior. For example, LPOP returns false for an empty list inside lua (instead of nil). While LPOP returns None in the python API. The script API of redipy has been altered to match the python API more closely. As the user doesn't code in lua directly the benefit of having a more consistent API outweighs the more complicated lua code that needs to be generated in the backend.
• Scripts aim to use python semantics as best as possible: In lua array indices start at 1. The script API uses a 0 based indexing system and transparently adjusts indices in the lua backend. Other, similar changes are performed as well.
• Scripts use JSON to pass arguments and return values: The arguments to the script are passed as JSON bytes for the lua backend. Keys are passed as is. The return value of the script is also converted into JSON when moving from lua to python. Note, that the empty dictionary ({}) and the empty list ([]) are indistinguishable in lua so None is returned instead if setting the return value to either of these.

TODOs

• implement more redis functions
• redipy.sql: A backend that provides the Redis functionality via SQL on traditional database systems, such as SQLite, PostgreSQL, or MySQL.
• switch_backend: dynamically switch backends at runtime which (potentially) migrates data to the new backend
• documentation

License

redipy is licensed under the Apache License (Version 2.0).

Contributing

The easiest way to contribute to redipy is to pick some redis API functions that have not (or not completely) been implemented in redipy yet. For this follow these steps:

1. Add the signature of the function to redipy.api.RedisAPI. Adjust as necessary from the redis spec to get a pythonic feel. Also, add the signature to redipy.api.PipelineAPI but with None as return value.
2. Implement the function in redipy.redis.conn.RedisConnection and redipy.redis.conn.PipelineConnection. This should be straightforward as there are not too many changes expected. Don't forget to convert bytes into strings via ...decode("utf-8").
3. Add tests to test/test_sanity.py to determine the function's behavior in lua (especially its edge cases).
4. If the lua behavior needs to be changed to provide a better feel you can mokeypatch the function call in redipy.redis.lua.LuaFnHook#adjust_redis_fn by either directly changing the returned expr for the execution graph or using a lua helper function via redipy.redis.lua.HELPER_FNS.
5. Next, add and implement the functionality in redipy.memory.state.Machine and add the appropriate redirects in redipy.memory.rt.LocalRuntime and redipy.memory.rt.LocalPipeline.
6. To make the new function accessible in scripts from the memory backend add an entry in redipy.memory.rt.LocalRuntime#redis_fn.
7. Add the approriate class or method in the right redipy.symbolic.r...py file. If it is a new class / file add an import to redipy.script.
8. Add a new test to verify the new function works inside a script for all backends. You can run make pytest FILE=test/...py to execute the test and make coverage-report to verify that the new code is executed.
9. Make sure make lint-all passes, as well as, all tests (make pytest) run without issue.

You can submit your patch as pull request here.

Feedback

If you have any questions, suggestions, or issues with redipy, please feel free to open an issue on GitHub. I would love to hear your feedback and improve redipy. Thank you!