Default arguments in Python - Step-by-Step Execution

Concept Flow - Default arguments

Function defined with default argument

↓

Function called

↓

Argument given

↓

Use given value

↓

Function body runs with chosen argument

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Return result

The function is defined with a default value for an argument. When called, if an argument is given, it uses that; otherwise, it uses the default.

Execution Sample

Python

def greet(name="Friend"):
    print(f"Hello, {name}!")

greet("Alice")
greet()

Defines a function with a default argument and calls it once with and once without an argument.

Execution Table

Step	Function Call	Argument Passed?	Value of 'name'	Action	Output
1	greet("Alice")	Yes	"Alice"	Use passed argument	Hello, Alice!
2	greet()	No	"Friend"	Use default argument	Hello, Friend!
3	End	-	-	No more calls	-

💡 All function calls completed, program ends.

Variable Tracker

Variable	Start	After Call 1	After Call 2	Final
name	-	"Alice"	"Friend"	-

Key Moments - 2 Insights

Why does the function print "Hello, Friend!" when called without an argument?

Because the function has a default argument 'name="Friend"', so when no argument is passed (see execution_table step 2), it uses the default value.

What happens if you pass an argument to the function?

The passed argument is used instead of the default (see execution_table step 1), so the function prints the greeting with the given name.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'name' during the second function call?

A "Alice"

B "Friend"

C None

D Error

💡 Hint

Check execution_table row 2 under 'Value of name'

At which step does the function use the default argument?

A Step 1

B Step 3

C Step 2

D Never

💡 Hint

Look at the 'Argument Passed?' column in execution_table

If you call greet("Bob"), what will be printed?

A Hello, Bob!

B Hello, Friend!

C Hello, Alice!

D Error

💡 Hint

See how the function uses passed arguments in execution_table step 1

Concept Snapshot

def function_name(arg=default):
    # function body

- If argument is passed, use it.
- Otherwise, use default value.
- Default arguments allow flexible function calls.

Full Transcript

This visual execution shows how Python functions use default arguments. The function greet is defined with a default argument name="Friend". When greet is called with an argument like "Alice", it uses that value. When called without an argument, it uses the default "Friend". The execution table tracks each call, showing the argument passed, the value used, and the output printed. The variable tracker shows how the variable 'name' changes with each call. Key moments clarify why default arguments work and when they are used. The quiz tests understanding by asking about values and behavior from the execution steps.