Argument order rules in Python - Step-by-Step Execution

Concept Flow - Argument order rules

Define function with parameters

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Call function with arguments

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Match arguments to parameters

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Positional

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Execute function body with matched values

This flow shows how Python matches arguments to function parameters by order: positional first, then keyword, and uses defaults if needed.

Execution Sample

Python

def greet(name, age=30, city='NY'):
    print(f"Name: {name}, Age: {age}, City: {city}")

greet('Alice', city='LA')

Calls greet with one positional and one keyword argument, showing how arguments match parameters.

Execution Table

Step	Parameter	Argument Provided	Value Assigned	Reason
1	name	'Alice'	'Alice'	Positional argument matches first parameter
2	age	None	30	No argument given, uses default value
3	city	'LA'	'LA'	Keyword argument overrides default
4	Function body	N/A	Prints: Name: Alice, Age: 30, City: LA	Execution with assigned values

💡 All parameters matched by positional, keyword, or default; function executes.

Variable Tracker

Parameter	Initial	After Assignment	Final
name	None	'Alice'	'Alice'
age	30 (default)	30	30
city	'NY' (default)	'LA'	'LA'

Key Moments - 3 Insights

Why can't we put a positional argument after a keyword argument in the call?

Because Python assigns positional arguments first in order, then keyword arguments. The execution_table shows 'name' assigned positionally first, then 'city' by keyword. Placing positional after keyword causes confusion in matching.

What happens if we omit an argument with a default value?

The default value is used. In the execution_table, 'age' has no argument provided, so it uses the default 30.

Can keyword arguments override positional arguments?

No, positional arguments are assigned first by order. Keyword arguments can only override parameters not already assigned positionally, as shown by 'city' in the table.

Visual Quiz - 3 Questions

Look at the execution_table, what value is assigned to 'age' parameter?

A 'LA'

B 'Alice'

C 30

D None

💡 Hint

Check the row where parameter is 'age' and see the 'Value Assigned' column.

At which step does the keyword argument get assigned?

A Step 2

B Step 3

C Step 1

D Step 4

💡 Hint

Look for the row where 'Argument Provided' is a keyword argument like 'city'.

If we call greet('Bob', 25), what value will 'city' have?

A 'NY'

B 'LA'

C 25

D 'Bob'

💡 Hint

Refer to variable_tracker for default values and how missing arguments use defaults.

Concept Snapshot

def func(pos1, pos2=default, *, kw1, kw2=default):
- Positional args fill parameters in order
- Keyword args assigned by name after positionals
- Default values used if no argument given
- Positional args cannot follow keyword args in call
- Mixing order correctly is required to avoid errors

Full Transcript

This visual trace shows how Python matches function call arguments to parameters. First, positional arguments are assigned in order to parameters. Then keyword arguments assign by name, overriding defaults if given. Parameters with default values use those defaults if no argument is provided. The example function greet has three parameters: name (required), age (default 30), and city (default 'NY'). The call greet('Alice', city='LA') assigns 'Alice' to name positionally, uses default 30 for age, and overrides city with 'LA' keyword. The execution table tracks each step of assignment and the final print output. Key points include that positional arguments must come before keyword arguments in calls, default values fill missing arguments, and keyword arguments cannot override positional assignments. The quiz tests understanding of these rules by referencing the execution steps and variable states.