Skip to main content

Partial function application with '...'

Project description


Partial argument application using ....


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 ....


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)

>>> halve = partial(truediv, ..., 2)  # functools.partial() cannot do this
>>> halve(3)

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)

Functions derived from f() automatically support ... themselves:

>>> h = g(2, ...)  # Supply g's first argument (y)
>>> h(3)  # Supply the final argument (z)

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)

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)


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.

The idea of using ... as a placeholder for function arguments and having it convert a function call into a partial function application is not new. AFAICS, it was first discussed on python-list in 2005, around the time partial() was first added to the Python standard library (PEP 309).


Run the following to install:

$ pip install partiell


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 nox to run all tests (as defined in

$ nox


Main development happens at Post issues and PRs there.

Project details

Download files

Download the file for your platform. If you're not sure which to choose, learn more about installing packages.

Source Distribution

partiell-0.0.2.tar.gz (12.1 kB view hashes)

Uploaded source

Built Distribution

partiell-0.0.2-py3-none-any.whl (9.0 kB view hashes)

Uploaded py3

Supported by

AWS AWS Cloud computing and Security Sponsor Datadog Datadog Monitoring Fastly Fastly CDN Google Google Download Analytics Microsoft Microsoft PSF Sponsor Pingdom Pingdom Monitoring Sentry Sentry Error logging StatusPage StatusPage Status page