> ## Documentation Index
> Fetch the complete documentation index at: https://genai.codewithsiva.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Packing and Unpacking

> Learn how to group multiple values together and extract them efficiently

Packing and unpacking are incredibly convenient features in Python that allow you to group multiple values into a single collection, or extract values from a collection directly into individual variables.

***

## Tuple Packing

**Packing** happens when you assign multiple values to a single variable without any brackets. Python automatically groups these values into a **tuple**.

```python theme={null}
# Packing three values into a single tuple
person = "Alice", 25, "Engineer"

print(person)        # ('Alice', 25, 'Engineer')
print(type(person))  # <class 'tuple'>
```

***

## Basic Unpacking

**Unpacking** is the reverse process. It extracts elements from a collection (tuple, list, set, or string) and assigns them to multiple variables in a single line.

```python theme={null}
person = ("Alice", 25, "Engineer")

# Unpacking the tuple into three separate variables
name, age, profession = person

print(name)        # Alice
print(age)         # 25
print(profession)  # Engineer
```

### Precaution: Variable Count Must Match

When doing basic unpacking, the number of variables on the left **must exactly match** the number of elements in the collection on the right.

```python theme={null}
numbers = (1, 2, 3)

# ERROR: Too many variables (expects 4 elements, got 3)
a, b, c, d = numbers  # ValueError: not enough values to unpack

# ERROR: Too few variables (expects 2 variables, got 3 elements)
x, y = numbers        # ValueError: too many values to unpack
```

***

## Extended Unpacking with `*` (Starred Expression)

What if you only want to extract a few elements and group the rest together? Python lets you use the asterisk `*` operator to capture multiple elements.

```python theme={null}
numbers = [1, 2, 3, 4, 5]

# Capture the first element, and pack the rest into a list
first, *rest = numbers
print(first)  # 1
print(rest)   # [2, 3, 4, 5]
```

You can place the `*` variable anywhere:

```python theme={null}
# Capture the last element, pack the rest
*body, last = [10, 20, 30, 40]
print(body)  # [10, 20, 30]
print(last)  # 40

# Capture the first and last, pack the middle
first, *middle, last = "Python"
print(first)   # 'P'
print(middle)  # ['y', 't', 'h', 'o']
print(last)    # 'n'
```

<Warning>
  **Rule:** You can only use **one** starred expression (`*`) in a single assignment. Otherwise, Python won't know how to divide the elements, raising a `SyntaxError`.
</Warning>

***

## Dictionary Unpacking with `**`

For dictionaries, you can use the double asterisk `**` operator to unpack key-value pairs. This is commonly used to merge multiple dictionaries together.

```python theme={null}
default_settings = {"theme": "light", "notifications": True}
user_settings = {"theme": "dark", "font_size": 14}

# Merge dictionaries (user settings will override defaults)
merged_settings = {**default_settings, **user_settings}
print(merged_settings)
# Output: {'theme': 'dark', 'notifications': True, 'font_size': 14}
```

***

## Unpacking in Loops

Unpacking makes iterating over complex data structures clean and readable.

### 1. Iterating over list of tuples/lists

```python theme={null}
pairs = [(1, "one"), (2, "two"), (3, "three")]

for number, name in pairs:
    print(f"{number} is spelled {name}")
```

### 2. Using `enumerate()`

The built-in `enumerate()` function returns pairs of `(index, item)`, which you can unpack in the loop header:

```python theme={null}
fruits = ["apple", "banana", "cherry"]

for index, fruit in enumerate(fruits):
    print(f"Index {index}: {fruit}")
```

### 3. Iterating over dictionary `.items()`

```python theme={null}
ages = {"Alice": 25, "Bob": 30}

for name, age in ages.items():
    print(f"{name} is {age} years old")
```

***

## Key Rules & Common Mistakes

<AccordionGroup>
  <Accordion title="ValueError: too many values to unpack">
    Happens when the number of elements on the right is greater than the number of variables on the left.

    ```python theme={null}
    # Wrong
    a, b = (1, 2, 3)  # ValueError!

    # Fix: Use * to capture the rest
    a, b, *rest = (1, 2, 3)
    ```
  </Accordion>

  <Accordion title="ValueError: not enough values to unpack">
    Happens when the number of variables on the left is greater than the number of elements on the right.

    ```python theme={null}
    # Wrong
    a, b, c = (1, 2)  # ValueError!
    ```
  </Accordion>

  <Accordion title="SyntaxError: two starred expressions in assignment">
    You cannot have more than one `*` variable on the left side.

    ```python theme={null}
    # Wrong
    *a, b, *c = [1, 2, 3, 4]  # SyntaxError!
    ```
  </Accordion>
</AccordionGroup>

***

## Practice & Exercises

To reinforce what you've learned in this section (Tuple packing, basic unpacking, starred expression unpacking, and loop unpacking), practice with these interactive notebooks:

<CardGroup cols={2}>
  <Card title="Follow-Along Practice" icon="laptop-code">
    Practice packing values, basic unpacking, starred unpacking (`*`), and loop/dictionary merging.

    [💻 VS Code](vscode://file/Users/sivaprasad/Downloads/python%20material/python4ai/public/notebooks/basics_exercises/Packing_Unpacking_Practice.ipynb) | [🚀 Colab](https://colab.research.google.com/github/prasad230776/python4ai/blob/master/public/notebooks/basics_exercises/Packing_Unpacking_Practice.ipynb) | <a href="/public/notebooks/basics_exercises/Packing_Unpacking_Practice.ipynb" download>📥 Download</a>
  </Card>

  <Card title="Practice Exercises" icon="pen-to-square">
    Test your knowledge with hands-on exercises on coordinate unpacking,Starred Marks partitioning, and configuration dictionary merging.

    [💻 VS Code](vscode://file/Users/sivaprasad/Downloads/python%20material/python4ai/public/notebooks/basics_exercises/Packing_Unpacking_Exercises.ipynb) | [🚀 Colab](https://colab.research.google.com/github/prasad230776/python4ai/blob/master/public/notebooks/basics_exercises/Packing_Unpacking_Exercises.ipynb) | <a href="/public/notebooks/basics_exercises/Packing_Unpacking_Exercises.ipynb" download>📥 Download</a>
  </Card>
</CardGroup>

## What's next?

Congratulations! You've completed Python Basics. Ready to start building programs?

<Card title="Building Programs" icon="graduation-cap" href="/functions">
  Learn about functions
</Card>