best way to distribute keyword arguments?

Question

What's the approved programming pattern for distributing keyword arguments among called functions?

Consider this contrived (and buggy) example:

def create_box(**kwargs): box = Box() set_size(box, **kwargs) set_appearance(box, **kwargs) def set_size(box, width=1, height=1, length=1): ... def set_appearance(box, material='cardboard', color='brown'): ...

Obviously the set_size() method will object to receiving material or color keyword arguments, just as set_appearance() will object to receiving width, height, or length arguments.

There's a valid argument that create_box() should make all of the keyword and defaults explicit, but the obvious implementation is rather unwieldy:

def create_box(width=1, height=1, length=1, material='cardboard', color='brown'): box = Box() set_size(box, width=width, height=height, length=length) set_appearance(box, material=material, color=color)

Is there a more Pythonic way to approach this?

IMO the kind of runtime bugs you can get by trying to hide a long list of args inside a kwargs can often be more unwieldy than just listing out the arguments explicitly — DaveBensonPhillips
– DaveBensonPhillips, Commented Nov 12, 2018 at 15:05

Rob Bricheno · Accepted Answer · 2018-11-12 15:00:23Z

You could add **kwargs as the last argument to the functions that would otherwise become annoyed.

def create_box(**kwargs): box = Box() set_size(box, **kwargs) set_appearance(box, **kwargs) def set_size(box, width=1, height=1, length=1, **kwargs): ... def set_appearance(box, material='cardboard', color='brown', **kwargs): ...

Chris_Rands · Accepted Answer · 2018-11-12 15:12:53Z

Assuming you can't alter set_size or set_appearance, you could filter kwargs depending on the expected keword arguments, I'm not sure if this is the most pythonic way though...

import inspect def create_box(**kwargs): box = None set_size_args = inspect.getargspec(set_size).args set_size(box, {k:v for k,v in kwargs.items() if k in set_size_args}) set_appearance_args = inspect.getargspec(set_appearance).args set_appearance(box, {k:v for k,v in kwargs.items() if k in set_appearance_args}) def set_size(box, width=1, height=1, length=1): pass def set_appearance(box, material='cardboard', color='brown'): pass create_box(width=1, height=1, length=1, material='', color='')

(use inspect.signature() for Python 3)

LeKhan9 · Accepted Answer · 2018-11-12 15:04:26Z

Hm, personally I would pass an object containing all of the params I needed. That way you're only passing one param all along.

Example:

class BoxDefinition: def __init__(self, width=1, height=1, length=1, material='cardboard', color='brown'): self.width = width self.height = height # and so on for the rest of the params ...

Internally in the each method you can read from this object:

def create_box(box_definition): box = Box() set_size(box, box_definition) set_appearance(box, box_definition) def set_size(box, box_definition): width = box_definition.width def set_appearance(box, box_definition): color = box_definition.color

Then you can call it like this:

definition = BoxDefinition(width=2, height=3, length=4) create_box(definition)

In fact, you can even make BoxDefinition and attribute of the Box class, and then the only thing you'd have to pass is Box.

This can get unwieldy if you have functions sharing the same kwarg but with different default values.
Fair point, I figured in the OPs scenario this would not be the case as the sets of kwargs are unique among functions

Collectives™ on Stack Overflow

best way to distribute keyword arguments?

3 Answers 3

Comments

Comments

2 Comments

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

Comments

2 Comments

Related