compose
The classic compose, with all the Pythonic features.
This compose follows the lead of functools.partial
and returns callable compose objects which:
- have a regular and unambiguous
repr, - retain correct signature introspection,
- allow introspection of the composed callables,
- can be type-checked,
- can be weakly referenced,
- can have attributes,
- will merge when nested, and
- can be pickled (if all composed callables can be pickled).
For async/await support, different variants of
compose are included.
Versioning
This library's version numbers follow the SemVer 2.0.0 specification.
Installation
pip install compose
For static type checking, also install the type hint stubs:
pip install compose-stubs
Usage
Basics
Import compose:
>>> from compose import composeAll the usual function composition you know and love:
>>> def double(x):
... return x * 2
...
>>> def increment(x):
... return x + 1
...
>>> double_then_increment = compose(increment, double)
>>> double_then_increment(1)
3Of course any number of functions can be composed:
>>> def double(x):
... return x * 2
...
>>> times_eight = compose(double, double, double)
>>> times_16 = compose(double, double, double, double)We still get the correct signature introspection:
>>> def f(a, b, c=0, **kwargs):
... pass
...
>>> def g(x):
... pass
...
>>> g_of_f = compose(g, f)
>>> import inspect
>>> inspect.signature(g_of_f)
<Signature (a, b, c=0, **kwargs)>And we can inspect all the composed callables:
>>> g_of_f.functions # in order of execution:
(<function f at 0x...>, <function g at 0x...>)compose instances flatten when nested:
>>> times_eight_times_two = compose(double, times_eight)
>>> times_eight_times_two.functions == times_16.functions
TrueWhen programmatically inspecting arbitrary callables, we
can check if we are looking at a compose instance:
>>> isinstance(g_of_f, compose)
Truecompose raises a TypeError when called with
no arguments or with any non-callable arguments:
>>> compose()
Traceback (most recent call last):
...
TypeError: compose() needs at least one argument>>> compose(increment, 'oops', increment)
Traceback (most recent call last):
...
TypeError: compose() arguments must be callable
async/await
We can compose async code by using acompose:
>>> import asyncio
>>> from compose import acompose
>>>
>>> async def get_data():
... # pretend this data is fetched from some async API
... await asyncio.sleep(0)
... return 42
...
>>> get_and_double_data = acompose(double, get_data)
>>> asyncio.run(get_and_double_data())
84acompose can compose any number of async
and regular functions, in any order:
>>> async def async_double(x):
... await asyncio.sleep(0)
... return x * 2
...
>>> async_times_16 = acompose(async_double, double, async_double, double)
>>> asyncio.run(async_times_16(1))
16acompose instances always return awaitable values,
even if none of the composed functions are async:
>>> awaitable_times_16 = acompose(double, double, double, double)
>>> asyncio.run(async_times_16(1))
16sacompose is like acompose, but sacompose
instances return an awaitable value only if any of
the composed functions return an awaitable value:
>>> from compose import sacompose
>>>
>>> regular_times_4 = sacompose(double, double)
>>> awaitable_times_4 = sacompose(double, async_double)
>>>
>>> regular_times_4(1)
4
>>> asyncio.run(awaitable_times_4(1))
4acompose and sacompose instances flatten when nested:
>>> acompose(f, acompose(f, f)).functions == (f, f, f)
True
>>> acompose(sacompose(f, f), f).functions == (f, f, f)
True
>>> sacompose(acompose(f, f), f).functions == (f, f, f)
True
>>> sacompose(f, sacompose(f, f)).functions == (f, f, f)
TrueBut compose instances don't flatten when nested
into acompose and sacompose, and vice versa:
>>> acompose(g_of_f).functions
(compose(<function g at 0x...>, <function f at 0x...>),)
>>> sacompose(g_of_f).functions
(compose(<function g at 0x...>, <function f at 0x...>),)
>>> compose(acompose(g, f)).functions
(acompose(<function g at 0x...>, <function f at 0x...>),)
>>> compose(sacompose(g, f)).functions
(sacompose(<function g at 0x...>, <function f at 0x...>),)compose, acompose, and sacompose
instances are all distinct types:
>>> isinstance(g_of_f, compose)
True
>>> isinstance(g_of_f, (acompose, sacompose))
False
>>> isinstance(async_times_16, acompose)
True
>>> isinstance(async_times_16, (compose, sacompose))
False
>>> isinstance(awaitable_times_4, sacompose)
True
>>> isinstance(awaitable_times_4, (compose, acompose))
False
