Python args and kwargs are used to pass a variable number of arguments to a function. In this article, I will like to take you through the awesomeness of args and kwargs in python and how they can be used, args stands for arguments while kwargs stands for keyword-arguments
Explaining arbitrary arguments
Arbitrary means a varying number of arguments, we don't always know how many arguments the user is going to pass in when they invoke a function, to accept a varying amount of argument developers turn to use args and kwargs.
Let's see the example below. Creating a function that will add two numbers together.
# *args = allows you to pass multiple non-key arguments
# **args = allows you to pass multiple keyword-arguments
# *unpacking operator
# 1. position 2. default 3. keyword 4. ARBITRARY
def add(a, b):
return a + b
print(add(1,2))
and we have our output which is:
3
now what is we will like to pass in 3 parameters?
def add(a, b):
return a + b
print(add(1,2,4))
well you can see it returns and error.
print(add(1,2,4))
TypeError: add() takes 2 positional arguments but 3 were given
So, what we can do is to modify our function in such a way that it takes varying number of arguments by using the *args. What happens when we do this is that we pack all our arguments into a tuple. Let me show you what am saying.
def add(*args):
print(type(args))
print(add(1,2,4))
and we have
<class 'tuple'>
as our results. So, we can use the build in methods of this tuple, or we can iterate over it. Let's iterate our tuple in the example below.
def add(*args):
total = 0
for arg in args:
total += arg
return total
print(add(1,2,4))
What we have done in the example below is to create variable named total to keep track of the total and also, we have total += the current arg that we are iterating over, and we have returned the total, and now we have our results.
7
and now we can add as many arguments as we want. See the example below.
def add(*args):
total = 0
for arg in args:
total += arg
return total
print(add(1,2,4,2,4,5))
and we now have our results as
18
You also change the name of the *args to anything let's say *nums and you will still have the same results because it is not as important as the unpacking operator.
def add(*nums):
total = 0
for num in nums:
total += num
return total
print(add(1,2,4,2,4,5))
output
18
and you can see we still have the same results.
Now let's try another example, a function that will display somebody's name.
def display_name(*args):
for arg in args:
print(arg, end="")
display_name("Noel", "Bansikah", "Tandap")
output:
NoelBansikahTandap
and you can pass in as many arguments that you want, maybe a title or your best food or game. Following a unique parameter name, you can pack whatever you want into a tuple as I mentioned above.
**kwargs
Now let's talk about kwargs. kwargs stands for keyword-arguments it allows you to pass multiple keyword arguments. See the example below, creating a function that prints an address. Whenever you pass arguments using kwargs, you pack them into a dictionary. To prove this, see below.
def print_address(**kwargs):
print(type(kwargs))
print_address(street="Mile 16",
city="Buea",
region="southwest region",
zip="00237")
output
<class 'dict'>
so, you can treat kwargs as if it's a dictionary. Let's iterate over the values to see our results.
def print_address(**kwargs):
for value in kwargs.values():
print(value)
print_address(street="Mile 16",
city="Buea",
region="southwest region",
zip="00237")
output
Mile 16
Buea
southwest region
00237
and now we have our values printed out, you can use the keys method to see the keys in the dictionary.
def print_address(**kwargs):
for key in kwargs.keys():
print(key)
print_address(street="Mile 16",
city="Buea",
region="southwest region",
zip="00237")
Output
street
city
region
zip
and we have our keys printed out.
To see everything both keys and values, you can use the items method.
def print_address(**kwargs):
for key,value in kwargs.items():
print(f"{key}: {value}")
print_address(street="Mile 16",
city="Buea",
region="southwest region",
zip="00237")
Output
street: Mile 16
city: Buea
region: southwest region
zip: 00237
and now you have all your outputs printed out.
Before we continue i will just like to recommend that if you don't have a detailed understanding about dictionaries, you can check this article Dictionaries in Python Explained.
In the example above, we can add in a vary number of keyword-arguments. Let's add apartment number.
def print_address(**kwargs):
for key,value in kwargs.items():
print(f"{key}: {value}")
print_address(street="Mile 16",
apt="100",//added apartment no.
city="Buea",
region="southwest region",
zip="00237")
Output
street: Mile 16
apt: 100
city: Buea
region: southwest region
zip: 00237
and now you can see apartment no. is packed with our previous arguments.
In our next example, we are going to use both *args and **kwargs for better understanding. We will print a shipping label.
def shipping_label(*args, **kwargs):
for arg in args:
print(arg, end="")
for value in kwargs.values():
print(value, end="")
shipping_label("Noel", "Bansikah", "Tandap",
street="Mile 16",
apt="100",
city="Buea",
region="southwest region",
zip="00237"
)
Output
Noel Bansikah Tandap Mile 16 100 Buea southwest region 00237
To print our output neat and separately, we can do this.
def shipping_label(*args, **kwargs):
for arg in args:
print(arg, end="")
print(f"{kwargs.get('street')} {kwargs.get('apt')}")
print(f"{kwargs.get('city')} {kwargs.get('state')}, {kwargs.get('zip')}")
shipping_label(" Noel ", " Bansikah ", " Tandap ",
street=" Mile 16 ",
apt=" 100 ",
city=" Buea ",
region=" southwest region ",
zip=" 00237 "
)
Output
Noel Bansikah Tandap Mile 16 100
Buea None, 00237
You can check if our print statement is setup to print an apartment and street, but the user doesn't have an apartment? as we can see above it will display none but we don't want that, so we can solve that by using if and else statements.
def shipping_label(*args, **kwargs):
for arg in args:
print(arg, end="")
if "apt" in kwargs:
print(f"{kwargs.get('street')} {kwargs.get('apt')}")
else:
print(f"{kwargs.get('street')}")
print(f"{kwargs.get('city')} {kwargs.get('state')}, {kwargs.get('zip')}")
shipping_label(" Noel ", " Bansikah ", " Tandap ",
street=" Mile 16 ",
# apt=" 100 ",
city=" Buea ",
region=" southwest region ",
zip=" 00237 "
)
output
Noel Bansikah Tandap Mile 16
Buea southwest region , 00237
and you can see that we have solved that problem of it displaying none.
Now what if a user has a POX, let's see how we can add that
def shipping_label(*args, **kwargs):
for arg in args:
print(arg, end="")
if "apt" in kwargs:
print(f"{kwargs.get('street')} {kwargs.get('apt')}")
elif "pobox" in kwargs:
print(f"{kwargs.get('street')}")
print(f"{kwargs.get('pobox')}")
else:
print(f"{kwargs.get('street')}")
print(f"{kwargs.get('city')} {kwargs.get('region')}, {kwargs.get('zip')}")
shipping_label(" Noel ", " Bansikah ", " Tandap ",
street=" Mile 16 ",
pobox=" #1001 ",
city=" Buea ",
region=" southwest region ",
zip=" 00237 "
)
Output
Noel Bansikah Tandap Mile 16
#1001
and now you can see the user's pobox is been added.
So that's all about arbitrary arguments and arbitrary keyword-arguments.
Summary
**args*: allows you to pass multiple non-key arguments, these arguments are packed in a tuple.
kwargs: allos you to pass multiple keyword-arguments and these arguments are packed in a dictionary.
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