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Python Object-Oriented Python (retired) Inheritance Instance Methods

Posted by Stephen Poole
Stephen Poole
9,361 Points

Could someone please remind me what **kwargs actually does?

I don't remember what **kwargs does. Could someone please explain it?

3 Answers

Dan Johnson
Dan Johnson
40,533 Points

**kwargs (short for keyword arguments) is a dictionary who's keys represent argument or attribute names. The two asterisks appended to the front mean that any keyword arguments passed into the function/method will be packed into the dictionary. This way you can pass any number of them as arguments:

class MyClass(object):
    my_first_attr = None
    my_second_attr = None

    def __init__(self, **kwargs):
        for key, value in kwargs.items():
            if hasattr(self, key):
                setattr(self, key, value)

    def __str__(self):
        return "{} {}".format(
            self.my_first_attr, 
            self.my_second_attr)


example = MyClass(
    my_first_attr = "Using packing", 
    my_second_attr = "to send arguments")

print(example)

You can actually use whatever name you'd like for it, kwargs is just the convention.

Stephen Poole
Stephen Poole
9,361 Points

Great, Thanks a lot Dan. Do you happen to know where the video is that the instructor did about the packing dictionaries and the use of the double asterisk? I feel like I need to rewatch it because I still find it confusing :/

I tried looking for the video on my own but can't seem to find it anywhere...

Dan Johnson
Dan Johnson
40,533 Points

The first mention of it I found in this course was in this video. It's mentioned at around 4:40.

Here's a simpler example if the video doesn't help:

def print_all(**kwargs):
    for key, value in kwargs.items():
        print("{} has the value {}".format(key, value))

print_all(send="in", whatever="you'd", like="to")
Stephen Poole
Stephen Poole
9,361 Points
Stephen Poole
Stephen Poole
9,361 Points

Ok awesome that makes a lot of sense! Just one more thing though: I thought the double asterisk was only used to unpack dictionaries... So when passing, send="in", whatever="you'd", like="to", to your print_all function, shouldn't you really be doing {"send": "in", "whatever": "you'd", "like": "to"}?

Or is the way you do it just another way of declaring a dictionary?

Dan Johnson
Dan Johnson
40,533 Points

It works for both packing and unpacking.

This is kind of a contrived example but it does both:

def pack(**kwargs):
    print("{works}".format(**kwargs))

pack(works="for both")
Stephen Poole
Stephen Poole
9,361 Points

Amazing, that clears everything up. Thanks again Dan, really big help!

Emmet Lowry
Emmet Lowry
10,196 Points
Emmet Lowry
Emmet Lowry
10,196 Points

When u call items on kwargs what items it refering to and what is the key and value represtent thx

Dan Johnson
Dan Johnson
40,533 Points

items returns a collection of the dictionary's key-value pairs. You can view the key as an index. and the value being whatever is stored at that index:

dictionary = {"Key": "Value"}
# Will print "Value"
print(dictionary["Key"])