Python*args and **kwargs
*args and **kwargs
By default, a function must be called with the correct number of arguments.
However, sometimes you may not know how many arguments that will be passed into your function.
*args and **kwargs allow functions to accept a unknown number of arguments.
Arbitrary Arguments - *args
If you do not know how many arguments will be passed into your function, add a* before the parameter name.
This way, the function will receive atuple of arguments and can access the items accordingly:
Example
Using *args to accept any number of arguments:
print("The youngest child is " + kids[2])
my_function("Emil", "Tobias", "Linus")
Arbitrary Arguments are often shortened to*args in Python documentation.
What is *args?
The*args parameter allows a function to accept any number of positional arguments.
Inside the function,args becomes a tuple containing all the passed arguments:
Example
Accessing individual arguments from *args:
print("Type:", type(args))
print("First argument:", args[0])
print("Second argument:", args[1])
print("All arguments:", args)
my_function("Emil", "Tobias", "Linus")
Using *args with Regular Arguments
You can combine regular parameters with *args.
Regular parameters must come before *args:
Example
for name in names:
print(greeting, name)
my_function("Hello", "Emil", "Tobias", "Linus")
In this example,"Hello" is assigned togreeting, and the rest are collected innames.
Practical Example with *args
*args is useful when you want to create flexible functions:
Example
A function that calculates the sum of any number of values:
total = 0
for num in numbers:
total += num
return total
print(my_function(1, 2, 3))
print(my_function(10, 20, 30, 40))
print(my_function(5))
Example
Finding the maximum value:
if len(numbers) == 0:
return None
max_num = numbers[0]
for num in numbers:
if num > max_num:
max_num = num
return max_num
print(my_function(3, 7, 2, 9, 1))
Arbitrary Keyword Arguments - **kwargs
If you do not know how many keyword arguments will be passed into your function, add two asterisks** before the parameter name.
This way, the function will receive adictionary of arguments and can access the items accordingly:
Example
Using **kwargs to accept any number of keyword arguments:
print("His last name is " + kid["lname"])
my_function(fname = "Tobias", lname = "Refsnes")
Arbitrary Keyword Arguments are often shortened to**kwargs in Python documentation.
What is **kwargs?
The**kwargs parameter allows a function to accept any number of keyword arguments.
Inside the function,kwargs becomes a dictionary containing all the keyword arguments:
Example
Accessing values from **kwargs:
print("Type:", type(myvar))
print("Name:", myvar["name"])
print("Age:", myvar["age"])
print("All data:", myvar)
my_function(name = "Tobias", age = 30, city = "Bergen")
Using **kwargs with Regular Arguments
You can combine regular parameters with **kwargs.
Regular parameters must come before **kwargs:
Example
print("Username:", username)
print("Additional details:")
for key, value in details.items():
print(" ", key + ":", value)
my_function("emil123", age = 25, city = "Oslo", hobby = "coding")
Combining *args and **kwargs
You can use both *args and **kwargs in the same function.
The order must be:
- regular parameters
- *args
- **kwargs
Example
print("Title:", title)
print("Positional arguments:", args)
print("Keyword arguments:", kwargs)
my_function("User Info", "Emil", "Tobias", age = 25, city = "Oslo")
Unpacking Arguments
The* and** operators can also be used whencalling functions to unpack (expand) a list or dictionary into separate arguments.
Unpacking Lists with *
If you have values stored in a list, you can use* to unpack them into individual arguments:
Example
Using * to unpack a list into arguments:
return a + b + c
numbers = [1, 2, 3]
result = my_function(*numbers) # Same as: my_function(1, 2, 3)
print(result)
Unpacking Dictionaries with **
If you have keyword arguments stored in a dictionary, you can use** to unpack them:
Example
Using ** to unpack a dictionary into keyword arguments:
print("Hello", fname, lname)
person = {"fname": "Emil", "lname": "Refsnes"}
my_function(**person) # Same as: my_function(fname="Emil", lname="Refsnes")
Remember: Use* and** in function definitions tocollect arguments, and use them in function calls tounpack arguments.
