catalogue: Super lightweight function registries for your library

catalogue is a tiny, zero-dependencies library that makes it easy to add
function (or object) registries to your code. Function registries are helpful
when you have objects that need to be both easily serializable and fully
customizable. Instead of passing a function into your object, you pass in an
identifier name, which the object can use to lookup the function from the
registry. This makes the object easy to serialize, because the name is a simple
string. If you instead saved the function, you'd have to use Pickle for
serialization, which has many drawbacks.

⏳ Installation

pip install catalogue

conda install -c conda-forge catalogue

⚠️ Important note: catalogue v2.0+ is only compatible with Python 3.6+.
For Python 2.7+ compatibility, use catalogue v1.x.

👩‍💻 Usage

Let's imagine you're developing a Python package that needs to load data
somewhere. You've already implemented some loader functions for the most common
data types, but you want to allow the user to easily add their own. Using
catalogue.create you can create a new registry under the namespace
your_package → loaders.

# YOUR PACKAGE
import catalogue

loaders = catalogue.create("your_package", "loaders")

This gives you a loaders.register decorator that your users can import and
decorate their custom loader functions with.

# USER CODE
from your_package import loaders

@loaders.register("custom_loader")
def custom_loader(data):
    # Load something here...
    return data

The decorated function will be registered automatically and in your package,
you'll be able to access all loaders by calling loaders.get_all.

# YOUR PACKAGE
def load_data(data, loader_id):
    print("All loaders:", loaders.get_all()) # {"custom_loader": <custom_loader>}
    loader = loaders.get(loader_id)
    return loader(data)

The user can now refer to their custom loader using only its string name
("custom_loader") and your application will know what to do and will use their
custom function.

# USER CODE
from your_package import load_data

load_data(data, loader_id="custom_loader")

❓ FAQ

But can't the user just pass in the `custom_loader` function directly?

Sure, that's the more classic callback approach. Instead of a string ID,
load_data could also take a function, in which case you wouldn't need a
package like this. catalogue helps you when you need to produce a serializable
record of which functions were passed in. For instance, you might want to write
a log message, or save a config to load back your object later. With
catalogue, your functions can be parameterized by strings, so logging and
serialization remains easy – while still giving you full extensibility.

How do I make sure all of the registration decorators have run?

Decorators normally run when modules are imported. Relying on this side-effect
can sometimes lead to confusion, especially if there's no other reason the
module would be imported. One solution is to use
entry points.

For instance, in spaCy we're starting to use function
registries to make the pipeline components much more customizable. Let's say one
user, Jo, develops a better tagging model using new machine learning research.
End-users of Jo's package should be able to write
spacy.load("jo_tagging_model"). They shouldn't need to remember to write
import jos_tagged_model first, just to run the function registries as a
side-effect. With entry points, the registration happens at install time – so
you don't need to rely on the import side-effects.

🎛 API

`function` `catalogue.create`

Create a new registry for a given namespace. Returns a setter function that can
be used as a decorator or called with a name and func keyword argument. If
entry_points=True is set, the registry will check for
Python entry points
advertised for the given namespace, e.g. the entry point group
spacy_architectures for the namespace "spacy", "architectures", in
Registry.get and Registry.get_all. This allows other packages to
auto-register functions.

Argument	Type	Description
`*namespace`	str	The namespace, e.g. `"spacy"` or `"spacy", "architectures"`.
`entry_points`	bool	Whether to check for entry points of the given namespace and pre-populate the global registry.
RETURNS	`Registry`	The `Registry` object with methods to register and retrieve functions.

architectures = catalogue.create("spacy", "architectures")

# Use as decorator
@architectures.register("custom_architecture")
def custom_architecture():
    pass

# Use as regular function
architectures.register("custom_architecture", func=custom_architecture)

`class` `Registry`

The registry object that can be used to register and retrieve functions. It's
usually created internally when you call catalogue.create.

`method` `Registry.init`

Initialize a new registry. If entry_points=True is set, the registry will
check for
Python entry points
advertised for the given namespace, e.g. the entry point group
spacy_architectures for the namespace "spacy", "architectures", in
Registry.get and Registry.get_all.

Argument	Type	Description
`namespace`	Tuple[str]	The namespace, e.g. `"spacy"` or `"spacy", "architectures"`.
`entry_points`	bool	Whether to check for entry points of the given namespace in `get` and `get_all`.
RETURNS	`Registry`	The newly created object.

# User-facing API
architectures = catalogue.create("spacy", "architectures")
# Internal API
architectures = Registry(("spacy", "architectures"))

`method` `Registry.contains`

Check whether a name is in the registry.

Argument	Type	Description
`name`	str	The name to check.
RETURNS	bool	Whether the name is in the registry.

architectures = catalogue.create("spacy", "architectures")

@architectures.register("custom_architecture")
def custom_architecture():
    pass

assert "custom_architecture" in architectures

`method` `Registry.call`

Register a function in the registry's namespace. Can be used as a decorator or
called as a function with the func keyword argument supplying the function to
register. Delegates to Registry.register.

`method` `Registry.register`

Register a function in the registry's namespace. Can be used as a decorator or
called as a function with the func keyword argument supplying the function to
register.

Argument	Type	Description
`name`	str	The name to register under the namespace.
`func`	Any	Optional function to register (if not used as decorator).
RETURNS	Callable	The decorator that takes one argument, the name.

architectures = catalogue.create("spacy", "architectures")

# Use as decorator
@architectures.register("custom_architecture")
def custom_architecture():
    pass

# Use as regular function
architectures.register("custom_architecture", func=custom_architecture)

`method` `Registry.get`

Get a function registered in the namespace.

Argument	Type	Description
`name`	str	The name.
RETURNS	Any	The registered function.

custom_architecture = architectures.get("custom_architecture")

`method` `Registry.get_all`

Get all functions in the registry's namespace.

Argument	Type	Description
RETURNS	Dict[str, Any]	The registered functions, keyed by name.

all_architectures = architectures.get_all()
# {"custom_architecture": <custom_architecture>}

`method` `Registry.get_entry_points`

Get registered entry points from other packages for this namespace. The name of
the entry point group is the namespace joined by _.

Argument	Type	Description
RETURNS	Dict[str, Any]	The loaded entry points, keyed by name.

architectures = catalogue.create("spacy", "architectures", entry_points=True)
# Will get all entry points of the group "spacy_architectures"
all_entry_points = architectures.get_entry_points()

`method` `Registry.get_entry_point`

Check if registered entry point is available for a given name in the namespace
and load it. Otherwise, return the default value.

Argument	Type	Description
`name`	str	Name of entry point to load.
`default`	Any	The default value to return. Defaults to `None`.
RETURNS	Any	The loaded entry point or the default value.

architectures = catalogue.create("spacy", "architectures", entry_points=True)
# Will get entry point "custom_architecture" of the group "spacy_architectures"
custom_architecture = architectures.get_entry_point("custom_architecture")

`method` `Registry.find`

Find the information about a registered function, including the module and path
to the file it's defined in, the line number and the docstring, if available.

Argument	Type	Description
`name`	str	Name of the registered function.
RETURNS	Dict[str, Union[str, int]]	The information about the function.

import catalogue

architectures = catalogue.create("spacy", "architectures", entry_points=True)

@architectures("my_architecture")
def my_architecture():
    """This is an architecture"""
    pass

info = architectures.find("my_architecture")
# {'module': 'your_package.architectures',
#  'file': '/path/to/your_package/architectures.py',
#  'line_no': 5,
#  'docstring': 'This is an architecture'}

`function` `catalogue.check_exists`

Check if a namespace exists.

Argument	Type	Description
`*namespace`	str	The namespace, e.g. `"spacy"` or `"spacy", "architectures"`.
RETURNS	bool	Whether the namespace exists.

Dependencies of catalogue (2).
Dependency	Optional
typing-extensions	false
zipp	false

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