args and kwargs in python for beginners

 

*args and **kwargs

Work with Python long enough, and eventually, you will encounter *args and **kwargs. These strange terms show up as parameters in function definitions. What do they do? Let's review a simple function:

def myfunc(a, b):
    return sum((a, b))*.05

print(myfunc(40, 60)

OUTPUT

5.0

This function returns 5% of the sum of a and b. In this example, a and b are positional arguments; that is, 40 is assigned to a because it is the first argument, and 60 to b. Notice also that to work with multiple positional arguments in the sum() function we had to pass them in as a tuple.

What if we want to work with more than two numbers? One way would be to assign a lot of parameters, and give each one a default value.

def myfunc(a=0,b=0,c=0,d=0,e=0):
    return sum((a,b,c,d,e))*.05



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myfunc(40,60,20)

OUTPUT

6.0

Obviously this is not a very efficient solution, and that's where *args comes in.

*args

When a function parameter starts with an asterisk, it allows for an arbitrary number of arguments, and the function takes them in as a tuple of values. Rewriting the above function:

def myfunc(*args):
&nbps;   return sum(args)*.05

myfunc(40,60,20)

OUTPUT

6.0

Notice how passing the keyword args into sum() function did the same thing as a tuple of arguments.
It is worth noting that the word args is itself arbitrary - any word will do so long as it's preceded by an asterisk. To demonstrate this:

def myfunc(*spam):
    return sum(spam)*.05




myfunc(40,60,20)

OUTPUT

6.0

**kwargs

Similarly, Python offers a way to handle arbitrary numbers of keyworded arguments. Instead of creating a tuple of values, **kwargs builds a dictionary of key/value pairs. For example:

def myfunc(*, **kwargs):
    if 'fruit' and 'juice' in kwargs:
    print(f"I like {' and '.join(args)} and my favorite fruit is {kwargs['fruit']}")
    &nsbp; &nsbp; print(f"May I have some {kwargs['juice']} juice?")
    else:
        pass

myfunc('eggs','spam',fruit='cherries',juice='orange')

I like eggs and spam and my favorite fruit is cherries

May I have some orange juice?

Placing keywords arguments ahead of positional arguments raises an exception:

myfumc(fruit='cherries',juice='orange','eggs','spam')

OUTPUT

  File "<ipython-input-8-fc6ff65addcc>", line 1
    myfunc(fruit='cherries',juice='orange','eggs','spam')
                                          ^
SyntaxError: positional argument follows keyword argument

As with args, you can use any name you'd like for keyworded arguments - kwargs is just a popular convention.

That's it! Now you should understand how *args and **kwargs provide the flexibility to work with arbitrary numbers of arguments!