Partial function application with '...'
Project description
partiell
Partial argument application using ...
.
Description
An enhanced version of functools.partial()
that
allows partially applying positional arguments from both the left and right
sides of the argument list.
We use ...
(the Ellipsis object) as a placeholder in the argument list for
the arguments that are not yet supplied. The object returned from partial()
also supports being called with ...
for further partial application.
Use partial
as a function decorator (@partial
) to make a function
automatically support partial argument application with ...
.
Usage
As a drop-in replacement for functools.partial()
:
>>> from partiell import partial
>>> from operator import mul, truediv
>>> double = partial(mul, 2) # same as functools.partial()
>>> double(5)
10
>>> halve = partial(truediv, ..., 2) # functools.partial() cannot do this
>>> halve(3)
1.5
As a function decorator to enable smoother partial function application:
>>> @partial
... def f(x, y, z):
... return x * 100 + y * 10 + z
f()
can now be called with ...
for partial function application:
>>> g = f(1, ...) # Supply first argument only (x)
>>> g(2, 3) # Supply the two remaining arguments (y, z)
123
Functions derived from f()
automatically support ...
themselves:
>>> h = g(2, ...) # Supply g's first argument (y)
>>> h(3) # Supply the final argument (z)
123
Using the ...
placeholder also allows supplying arguments right-to-left:
>>> i = f(..., 3) # Supply last argument only (z)
>>> i(1, 2) # Supply the remaining arguments (x, y)
123
We can even supply arguments from both ends simultaneously:
>>> j = f(1, ..., 3) # Supply first and last argument (x, z)
>>> j(2) # Supply the remaining argument (y)
123
Discussion
Using ...
as a placeholder for future function arguments allows for a
"functional light" programming style that is somewhere between the verbosity
of invoking partial() explicitly and the implicit currying provided by e.g.
the @curry
decorator in PyMonad.
Installation
Run the following to install:
$ pip install partiell
Development
To work on partiell, clone this repo, and run the following (in a virtualenv) to get everything you need to develop and run tests:
$ pip install -e .[dev]
Alternatively, if you are using Nix, simply use the bundled shell.nix
to get
a development environment:
$ nix-shell
Use the run_tests.sh
script to run all tests:
$ ./run_tests.sh
Contributing
Main development happens at https://github.com/jherland/partiell/. Post issues and PRs there.
Project details
Release history Release notifications | RSS feed
Download files
Download the file for your platform. If you're not sure which to choose, learn more about installing packages.