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 <https://semver.org/spec/v2.0.0.html>_.

Installation

::

pip install compose

For static type checking, also install the type hint stubs <https://pypi.org/project/compose-stubs>_:

::

pip install compose-stubs

Usage

Basics

Import ``compose``:

.. code:: python

    >>> from compose import compose

All the usual function composition you know and love:

.. code:: python

    >>> def double(x):
    ...     return x * 2
    ...
    >>> def increment(x):
    ...     return x + 1
    ...
    >>> double_then_increment = compose(increment, double)
    >>> double_then_increment(1)
    3

Of course any number of functions can be composed:

.. code:: python

    >>> 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:

.. code:: python

    >>> 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:

.. code:: python

    >>> g_of_f.functions  # in order of execution:
    (<function f at 0x...>, <function g at 0x...>)

``compose`` instances flatten when nested:

.. code:: python

   >>> times_eight_times_two = compose(double, times_eight)
   >>> times_eight_times_two.functions == times_16.functions
   True

When programmatically inspecting arbitrary callables, we
can check if we are looking at a ``compose`` instance:

.. code:: python

    >>> isinstance(g_of_f, compose)
    True

``compose`` raises a ``TypeError`` when called with
no arguments or with any non-callable arguments:

.. code:: python

    >>> compose()
    Traceback (most recent call last):
        ...
    TypeError: compose() needs at least one argument

.. code:: python

    >>> 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:

.. code:: python

>>> 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())
84

acompose can compose any number of async and regular functions, in any order:

.. code:: python

>>> 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))
16

acompose instances always return awaitable values, even if none of the composed functions are async:

.. code:: python

>>> awaitable_times_16 = acompose(double, double, double, double)
>>> asyncio.run(async_times_16(1))
16

sacompose is like acompose, but sacompose instances return an awaitable value only if any of the composed functions return an awaitable value:

.. code:: python

>>> 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))
4

acompose and sacompose instances flatten when nested:

.. code:: python

>>> 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)
True

But compose instances don't flatten when nested into acompose and sacompose, and vice versa:

.. code:: python

>>> 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:

.. code:: python

>>> 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