Basics

Import composable:

>>> from compose_operator import composable

A simple inline composition:

>>> stringify_as_integer = composable(int) | str
>>> stringify_as_integer(12.3)
'12'

Naturally, the result of | on a composable function is also composable, so you can chain it:

>>> (composable(int) | str | list)(12.3)
['1', '2']

You can also use composable as a decorator:

>>> @composable
... def my_stringify(thing):
...     return f'hello {thing}'
...
>>> stringify_as_integer = int | my_stringify
>>> stringify_as_integer(12.3)
'hello 12'

composable is “sticky”

composable will stick to callable return values, so it works out-of-the-box with currying, partial application, and so on:

>>> import functools
>>> import operator
>>> import toolz
>>>
>>> partial = composable(functools.partial)
>>> add1 = partial(operator.add, 1)
>>> (add1 | str)(2)
'3'
>>> curry = composable(toolz.curry)
>>> add = curry(operator.add)
>>> (add(2) | float)(2)
4.0

composable also sticks to the results of method binding, so if you make a composable method, or assign a function composed with the | operator as a method, it “just works”:

>>> class Adder:
...     def __init__(self, value):
...         self._value = value
...
...     @composable
...     def add(self, thing):
...         return thing + self._value
...
...     add_then_stringify = add | str
...
>>> adder = Adder(42)
>>> (adder.add | str)(8)
'50'
>>> adder.add_then_stringify(9)
'51'

Composable Classes

If you want to decorate a class so that the class is composable, use @composable_constructor - that way, normal class functionality such as | for type unions still works:

>>> from compose_operator import composable_constructor
>>>
>>> from dataclasses import dataclass
>>>
>>> @composable_constructor
... @dataclass
... class MyClass:
...     x: int
...
>>> isinstance(1, int | MyClass)
True
>>> isinstance("hello!", int | MyClass)
False
>>> isinstance(MyClass(0), int | MyClass)
True
>>> (operator.add | MyClass)(3, 2)
MyClass(x=5)

composable takes precedence over composable_constructor, so you can still force | to do composition instead of type union if you need to:

>>> (composable(int) | MyClass)("6")
MyClass(x=6)
>>> (int | composable(MyClass))("7")
MyClass(x=7)

Composable Callable Objects

If you are defining a class with a __call__ method, you can make its instances automatically composable by using composable_instances:

>>> from compose_operator import composable_instances
>>>
>>> @composable_instances
... class Greeter:
...     def __init__(self, target):
...         self._target = target
...     def __call__(self):
...         return f"Hello, {self._target}!"
...
>>> world_greeter = Greeter("world")
>>> world_greeter()
'Hello, world!'
>>> (world_greeter | list)()
['H', 'e', 'l', 'l', 'o', ',', ' ', 'w', 'o', 'r', 'l', 'd', '!']