Function definition and syntax in Python - Step-by-Step Execution

Concept Flow - Function definition and syntax

Start

↓

Define function with def

↓

Function name and parameters

↓

Function body indented

↓

Function ends

↓

Call function to run it

↓

Function runs and returns

↓

End

This flow shows how a function is defined with def, given a name and parameters, has an indented body, and then is called to run.

Execution Sample

Python

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

greet("Alice")

Defines a function greet that prints a hello message, then calls it with 'Alice'.

Execution Table

Step	Action	Evaluation	Result
1	Define function greet with parameter name	No output	Function greet created
2	Call greet with argument 'Alice'	name = 'Alice'	Function greet starts
3	Execute print inside greet	Prints 'Hello, Alice!'	Output: Hello, Alice!
4	Function greet ends	No return value	Back to main program

💡 Function greet has finished running after printing the message.

Variable Tracker

Variable	Start	After call greet('Alice')	Final
name	undefined	'Alice'	undefined after function ends

Key Moments - 3 Insights

Why do we indent the function body?

Indentation shows which lines belong inside the function, as seen in step 3 where print is indented under greet.

What happens if we call the function without parentheses?

Without parentheses, the function does not run; step 2 shows calling greet() with parentheses runs the function.

Is the variable 'name' available outside the function?

No, 'name' exists only inside the function during step 2 and 3, then disappears after step 4.

Visual Quiz - 3 Questions

Look at the execution table, what is the value of 'name' during step 3?

A 'Alice'

B undefined

C None

D greet

💡 Hint

Check the 'Evaluation' column at step 3 in the execution table.

At which step does the function greet actually run its code?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look for the step where the print statement executes in the execution table.

If we remove the parentheses in greet("Alice"), what changes in the execution table?

A Error occurs at step 2

B Function greet runs twice

C Function greet is defined but never called

D Output prints twice

💡 Hint

Refer to step 2 where the function call happens with parentheses.

Concept Snapshot

def function_name(parameters):
    indented function body

- Use def to define a function.
- Function body must be indented.
- Call function with parentheses to run it.
- Parameters receive input values.

Full Transcript

This example shows how to define a function in Python using def, give it a name and parameters, write an indented body, and then call it with parentheses to run. The variable inside the function exists only during the function call. Indentation is important to mark the function body. Calling the function without parentheses does not run it.