Steven D'Aprano <st...@pearwood.info> writes:
> A work colleague wanted to pass an argument starting with "-" to a
> function.
>
> Apparently he didn't have a specific argument in mind. He just wanted
> to test the function to breaking point by passing invalid argument
> names.
That seems a reasonable test.
>>> kwargs = {
... 'spam': 13,
... 'eggs': 17,
... '-beans': 11,
... }
>>> foo(**kwargs) # Should this fail?
It exposes a design smell; by capturing ‘**kwargs’, a function has
deiberately not specified which keyword arguments it will accept.
>>> def foo_captures_kwargs(*args, **kwargs):
... for (name, value) in kwargs.items():
... print("Got argument {name}={value!r}".format(
... name=name, value=value))
...
>>> foo_captures_kwargs(**kwargs)
Got argument eggs=17
Got argument spam=13
Got argument -beans=11
Still not a bug in Python IMO. It may be a bug in the program; the
design of the function doesn't provide any way to know.
Perhaps the design can be improved by not using ‘**kwargs’ at all, and
instead using a specific set of keyword-only arguments.
>>> def foo_names_every_argument(*, spam="Lorem", eggs="ipsum"):
... print("Got argument {name}={value!r}".format(
... name='spam', value=spam))
... print("Got argument {name}={value!r}".format(
... name='eggs', value=eggs))
...
>>> foo_names_every_argument(**kwargs)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: foo_names_every_argument() got an unexpected keyword argument
'-beans'
This is IMO another good reason to migrate ASAP to Python 3; better
design is easier that before.
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_o__) |
Ben Finney
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