Python function: how to use the argument in kwargs

Question

When writing functions with **kwargs, the syntax becomes not as clean as without it. For example

def func(x, y):
    print(x + y)

will become

def func(**kwargs):
    print(kwargs["x"] + kwargs["y"])

Any suggestions to make calling kwargs nicer and more clean?

Answer 1

argparse mentioned in the other answer uses kwargs a lot. It gives a lot of flexibility when handling a large number optional parameters, but the syntax is not 'simple. You need to handle the case where the user does not provide a value. The dictionary get is good for that:

In [241]: def func(**kwargs): 
     ...:     print(kwargs) 
     ...:     x = kwargs.get('x',0) 
     ...:     y = kwargs.get('y',0) 
     ...:     return x + y 
     ...:      
     ...:                                                                       
In [242]: func(x=1, y=2)                                                        
{'x': 1, 'y': 2}
Out[242]: 3
In [243]: func(**{'x':1, 'y':2})                                                
{'x': 1, 'y': 2}
Out[243]: 3

Also use if 'x' in kwargs: or for key in kwargs:

With keyword parameters, you can use the same **dict style of input:

In [244]: def func(x=0, y=2): 
     ...:     return x + y                                                                       
In [245]: func(**{'x':1, 'y':2})                                                
Out[245]: 3

You could unpack the kwargs with:

In [246]: def func(**kwargs): 
     ...:     x, y = kwargs.values() 
     ...:     return x + y 
     ...:                                                                       
In [247]: func(**{'x':1, 'y':2})                                                
Out[247]: 3

but in that case you might as well use *args:

In [248]: def func(*args): 
     ...:     x, y = args 
     ...:     return x + y 
     ...:                                                                       
In [249]: func(1,2)                                                             
Out[249]: 3

Part of the code for argparse.Namespace:

class Namespace(_AttributeHolder):
    def __init__(self, **kwargs):
        for name in kwargs:
            setattr(self, name, kwargs[name])

This converts the dictionary keys into object attributes. argparse also notes that you can go the other direction with vars(args), getting a dictionary from an object's attributes.