python : positional argument, default argument

In Python, positional arguments and default arguments are used when passing values to a function.
1. Positional arguments
A positional argument is passed according to the position (order) of the parameter.

def student(name, age):
    print(name)
    print(age)

student("Sajin", 20)

Output :

Sajin
20

Step-by-step
Parameter Argument
name "Sajin"
age 20

Python matches values based on their order.

If you change the order:

student(20, "Sajin")

Output:

20
Sajin

Here, name = 20 and age = "Sajin".

2. Default arguments
A default argument has a value assigned in the function definition.

If you don't pass a value, Python uses the default.

def login(username="admin", password="1234"):
    print(username, password)

login()

Output:

admin 1234

You can also pass your own values:

login("Sajin", "5678")

Output:

Sajin 5678

Step-by-Step:

def login(username="admin", password="1234"):
    print(username, password)

login("Sajin")

Output:

Sajin 1234

• "Sajin" replaces the default username.
• Password is not provided.
• So Python uses the default password "1234".

3. Positional + Default arguments

def login(username, password="1234"):
    print(username, password)

login("Sajin")

Output:

Sajin 1234

Here:

• username is a required positional parameter.
• password is a default parameter.

You can also provide both:

login("Joe", "5678")

Output:

Joe 5678

Important rule: A parameter without a default value cannot come after a parameter with a default value.
❌ Incorrect:

def login(username="admin", password):
    print(username, password)

✅ Correct:

def login(username, password="1234"):
    print(username, password)