Proper way to use **kwargs in Python Proper way to use **kwargs in Python python python

Proper way to use **kwargs in Python


You can pass a default value to get() for keys that are not in the dictionary:

self.val2 = kwargs.get('val2',"default value")

However, if you plan on using a particular argument with a particular default value, why not use named arguments in the first place?

def __init__(self, val2="default value", **kwargs):


While most answers are saying that, e.g.,

def f(**kwargs):    foo = kwargs.pop('foo')    bar = kwargs.pop('bar')    ...etc...

is "the same as"

def f(foo=None, bar=None, **kwargs):    ...etc...

this is not true. In the latter case, f can be called as f(23, 42), while the former case accepts named arguments only -- no positional calls. Often you want to allow the caller maximum flexibility and therefore the second form, as most answers assert, is preferable: but that is not always the case. When you accept many optional parameters of which typically only a few are passed, it may be an excellent idea (avoiding accidents and unreadable code at your call sites!) to force the use of named arguments -- threading.Thread is an example. The first form is how you implement that in Python 2.

The idiom is so important that in Python 3 it now has special supporting syntax: every argument after a single * in the def signature is keyword-only, that is, cannot be passed as a positional argument, but only as a named one. So in Python 3 you could code the above as:

def f(*, foo=None, bar=None, **kwargs):    ...etc...

Indeed, in Python 3 you can even have keyword-only arguments that aren't optional (ones without a default value).

However, Python 2 still has long years of productive life ahead, so it's better to not forget the techniques and idioms that let you implement in Python 2 important design ideas that are directly supported in the language in Python 3!


I suggest something like this

def testFunc( **kwargs ):    options = {            'option1' : 'default_value1',            'option2' : 'default_value2',            'option3' : 'default_value3', }    options.update(kwargs)    print optionstestFunc( option1='new_value1', option3='new_value3' )# {'option2': 'default_value2', 'option3': 'new_value3', 'option1': 'new_value1'}testFunc( option2='new_value2' )# {'option1': 'default_value1', 'option3': 'default_value3', 'option2': 'new_value2'}

And then use the values any way you want

dictionaryA.update(dictionaryB) adds the contents of dictionaryB to dictionaryA overwriting any duplicate keys.


matomo