default arguments.

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🐍 Default Arguments in Python

Understanding Default Values in Function Parameters

1. What is a Default Argument?

A default argument is a value assigned to a function parameter when the function is defined.

If the caller does not provide a value for that parameter, Python automatically uses the default value.

2. Syntax

def function_name(parameter=default_value):
    statements

The parameter is assigned a value using the = operator.

3. Simple Example

def greet(name="Student"):
    print("Hello", name)

greet()
greet("Bijan")

Output

Hello Student Hello Bijan

In the first function call, no argument is supplied. Therefore, Python uses "Student".

In the second call, "Bijan" is supplied, so the default value is replaced.

4. How Default Arguments Work

Function Definition

→

Default Value

→

Function Call

→

Argument Given?

→

Use Given / Default Value

5. Multiple Default Arguments

def student(name, course="BCA", year=1):
    print("Name:", name)
    print("Course:", course)
    print("Year:", year)

student("Rahul")

Output

Name: Rahul Course: BCA Year: 1

Here, course and year have default values.

6. Overriding a Default Argument

def student(name, course="BCA", year=1):
    print(name, course, year)

student("Rahul")
student("Anita", "BSc", 2)

Output

Rahul BCA 1 Anita BSc 2

When values are provided during the function call, they replace the default values.

7. Default Argument with Return

def power(number, exponent=2):
    return number ** exponent

print(power(5))
print(power(5, 3))

Output

25 125

The default exponent is 2. Therefore, power(5) calculates 5².

When 3 is supplied, the calculation becomes 5³.

8. Important Rule

Important: Parameters with default values should generally be placed after parameters without default values.

Correct:

def student(name, age=18):
    print(name, age)

Incorrect:

def student(age=18, name):
    print(name, age)

The second form produces a SyntaxError.

9. Parameter vs Default Argument

Concept	Example	Meaning
Parameter	name	Variable that receives a value.
Default Parameter	name="Student"	Parameter with a predefined value.
Argument	"Bijan"	Actual value passed during the function call.

10. Advantages of Default Arguments

♻ Reusability

The same function can work with or without optional values.

⚡ Simplicity

The caller does not need to provide every argument.

🧩 Flexibility

Default values can be replaced whenever necessary.

📖 Readability

Functions become easier to use and understand.

11. Interactive Demonstration

Click the buttons to understand how default arguments work.

Select an example.

12. Important Points for Examination

• A default argument has a predefined value.
• Default values are specified while defining the function.
• If an argument is omitted, the default value is used.
• A supplied argument overrides the default value.
• Non-default parameters should come before default parameters.
• Default arguments are useful for optional parameters.

13. Quick Summary

def function_name(parameter=default_value):
    statements

function_name()
function_name(value)

Remember:

No argument → Default value is used
Argument supplied → Supplied value is used

Python Programming Notes | Default Arguments
Created by Bijan Krishna Paul

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