All the IPython Notebooks in Python Advanced Topics lecture series by Dr. Milaan Parmar are available @ GitHub
*args and **kwargs¶In this class, we will learn about Python *args and **kwargs ,their uses and functions with examples.
In programming, we define a function to make a reusable code that performs similar operation. To perform that operation, we call a function with the specific value, this value is called a function argument in Python.
We would recommend you to read Python Function and Python Function Arguments.
Suppose, we define a function for addition of 3 numbers.
# Example 1: Function to add 3 numbers
def adder(x,y,z):
print("sum:",x+y+z)
adder(12,15,19)
sum: 46
Explanation:
In above program we have adder() function with three arguments x, y and z. When we pass three values while calling adder() function, we get sum of the 3 numbers as the output.
Lets see what happens when we pass more than 3 arguments in the adder() function.
def adder(x,y,z):
print("sum:",x+y+z)
adder(5,10,15,20,25)
--------------------------------------------------------------------------- TypeError Traceback (most recent call last) <ipython-input-2-986e6d871071> in <module> 2 print("sum:",x+y+z) 3 ----> 4 adder(5,10,15,20,25) TypeError: adder() takes 3 positional arguments but 5 were given
Explanation:
In the above program, we passed 5 arguments to the adder() function instead of 3 arguments due to which we got TypeError.
*args and **kwargs in Python¶In Python, we can pass a variable number of arguments to a function using special symbols. There are two special symbols:
*args (Non Keyword Arguments)**kwargs (Keyword Arguments)We use *args and **kwargs as an argument when we are unsure about the number of arguments to pass in the functions.
As in the above example we are not sure about the number of arguments that can be passed to a function. Python has *args which allow us to pass the variable number of non keyword arguments to function.
In the function, we should use an asterisk * before the parameter name to pass variable length arguments.The arguments are passed as a tuple and these passed arguments make tuple inside the function with same name as the parameter excluding asterisk *.
# Example 2: Using *args to pass the variable length arguments to the function
def adder(*num):
sum = 0
for n in num:
sum = sum + n
print("Sum:",sum)
adder(3,6)
adder(3,5,6,7)
adder(1,2,3,6,9)
Sum: 9 Sum: 21 Sum: 21
Explanation:
In the above program, we used *num as a parameter which allows us to pass variable length argument list to the adder() function. Inside the function, we have a loop which adds the passed argument and prints the result. We passed 3 different tuples with variable length as an argument to the function.
**kwargs¶Python passes variable length non keyword argument to function using *args but we cannot use this to pass keyword argument. For this problem Python has got a solution called **kwargs, it allows us to pass the variable length of keyword arguments to the function.
In the function, we use the double asterisk ** before the parameter name to denote this type of argument. The arguments are passed as a dictionary and these arguments make a dictionary inside function with name same as the parameter excluding double asterisk **.
# Example 3: Using **kwargs to pass the variable keyword arguments to the function
def intro(**data):
print("\nData type of argument:",type(data))
for key, value in data.items():
print("{} is {}".format(key,value))
intro(Firstname="Amy", Lastname="Barn", Age=24, Phone=1234567890)
intro(Firstname="Arthur", Lastname="Hunt", Email="arthurhunt@yesmail.com", Country="Atlantis", Age=27, Phone=9976563219)
Data type of argument: <class 'dict'> Firstname is Amy Lastname is Barn Age is 24 Phone is 1234567890 Data type of argument: <class 'dict'> Firstname is Arthur Lastname is Hunt Email is arthurhunt@yesmail.com Country is Atlantis Age is 27 Phone is 9976563219
Explanation:
In the above program, we have a function intro() with **data as a parameter. We passed two dictionaries with variable argument length to the intro() function. We have for loop inside intro() function which works on the data of passed dictionary and prints the value of the dictionary..
*args and **kwargs are special keyword which allows function to take variable length argument.*args passes variable number of non-keyworded arguments list and on which operation of the list can be performed.**kwargs passes variable number of keyword arguments dictionary to function on which operation of a dictionary can be performed.*args and **kwargs make the function flexible.