Basic usage¶

Files layout¶

It is recommended to create dedicated folder in your project for your LUA scripts.

A good convention is to name it lua as it is both obvious and short to type.

You can then organize your scripts in whichever structure you want: with or without subfolders, one for each function or several functions per file. It’s really up to you. Just make sure you stay consistent.

A common pattern to get a variable that points to that root folder for scripts is to write:

LUA_SCRIPTS_PATH = os.path.join(
    os.path.dirname(os.path.abspath(__file__)),
    'lua',
)

Initialization¶

In a typical case, you want to load all your scripts in the initialization of your executable or service. The easiest way to achieve that is to simply call:

from redis_lua import load_all_scripts

scripts = load_all_scripts(path=LUA_SEARCH_PATH)

Calling scripts¶

Calling a script is easy:

result = scripts['foo'].get_runner(client=client)(
    my_key='my_key',
    my_arg='my_arg',
)

result will contain the result as given by the LUA script.

Advanced usage¶

redis_lua does not only provide helpers to deal with LUA scripts but also extends the LUA syntax to add new features.

Keys, arguments and return values¶

redis_lua helps you calling LUA scripts by allowing you to name your keys and arguments.

To do that, you can use the %key and %arg instructions. Both are pretty similar but don’t have the exact same syntax.

Keys¶

The %key instruction takes one mandatory parameter that is the name of the key. Keys and arguments share the same namespace which means you can only have one key or argument with a given name. To avoid ambiguity on the Python side, it is recommended that you suffix your keys with _key as to make it obvious you are dealing with a Redis key.

Here is an example of usage of the %key instruction:

%key player_key

This exposes a player_key function argument on the Python side which expects to be set with a Redis key (a string).

Arguments¶

The %arg instructions takes one mandatory parameter which is the name of the argument, like %key, and one optional parameter, which is the type of the argument.

Here is an example of usage of the %arg instruction:

%arg count int

This exposes a count function argument on the Python side which expects to be set with a Python integer value.

Here is a list of the supported types:

Aliases	Python type	LUA type
int	int	number
integer	int	number
string	str	string
str	str	string
bool	bool	number
boolean	bool	number
dict	dict	array (dict)
dictionary	dict	array (dict)
list	list	array
array	list	array

If no type is specified, the argument is transfered as-is to the script using the default argument conversion of pyredis. It is unspecified what this conversion does exactly.

Return values¶

The %return statement indicates the expected return type of the script when converting the value for return on the Python side. The user is responsible for providing a value that can correctly be cast to the registered return type.

Here is an example of usage of the %return instruction:

%return dict

This cause the value returned by the script to be interpreted as a JSON-encoded dictionary and converted implicitely into a Python dict.

Here is a list of the expected LUA types for each type:

Aliases	Python type	LUA type
int	int	number
integer	int	number
string	str	string
str	str	string
bool	bool	number
boolean	bool	number
dict	dict	JSON-encoded array (dict)
dictionary	dict	JSON-encoded array (dict)
list	list	JSON-encoded array
array	list	JSON-encoded array

On the LUA side, you may want to use the following pattern for the list and dict return types:

return cjson.encode({
   a=1,
   b="2",
   c={
     d=42,
   },
})

Warning

There can be at most one %return statement in a given script.

Script inclusion¶

One of the main problems of Redis LUA scripts is that it doesn’t support the LUA require keyword. To circumvent that limitation, the LUA script parsing logic in redis_lua handles %include statements, like so:

-- The "foo.lua" script in the same folder defines the "create_foo()"
-- function.

%include "foo"

local t = create_foo(1, "a");

%include takes a single argument, which is the complete name (with any relative path component) of the LUA script to include, without its .lua extension.

So if you have two scripts foo/a.lua and bar/b.lua each in a different subfolder of the lua directory, you can include bar/b.lua in foo/a.lua by simply adding the following %include statement:

%include '../bar/b'

Warning

For the inclusion system to work properly, all scripts must either been have loaded by the same call, or by different calls but using the same script cache.

Multiple inclusion¶

By default, redis-lua allows multiple inclusions of the same file several times. This can cause issues when including different scripts that include the same subscripts which conflict with each other.

To prevent side-effects caused by multiple inclusion of the same scripts, you can use the following statement, anywhere in the script:

%pragma once

Note

This behavior is new since version 2.0.0.

In previous versions, the default behavior was as-if %pragma once was defined implicitely in each script.