neutrinoceros / future_positional_only

positional_defaults

Python package to set defaults for any positional-only parameter

This tiny Python package contains a decorator @fpo which lets you specify default arguments for any positional-only parameter, no matter where it appears in the argument list.

Installation

COMPILE_FPO=1 python -m pip install -e .

Usage

Use the @fpo decorator to set default values for future-positional-only parameters (i.e. those before the positional-only indicator /):

from future_positional_only import fpo

@fpo({'start': 0})
def myrange(start, stop, step=1):
    ...

Signatures

Left-defaulted functions come with the correct signature:

>>> from inspect import signature
>>> signature(myrange)
<DefaultsSignature (start=0, stop, /, step=1)>
>>> signature(greet)
<DefaultsSignature (greeting='Welcome', prefix='Mrs', forename='Alice', surname, /, suffix='Esq')>

These show up correctly in the usual places such as help():

>>> help(myrange)

Help on function myrange:

myrange(start=0, stop, /, step=1)

>>> help(greet)

Help on function greet:

greet(greeting='Welcome', prefix='Mrs', forename='Alice', surname, /, suffix='Esq')

Performance

When the package is compiled as a native extension (which is what pip will deliver in the majority of cases), functions with positional defaults have comparable performance with respect to their undecorated functions.