> ## Documentation Index
> Fetch the complete documentation index at: https://python4ai.codewithsiva.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Parameters

> Pass data into your functions

## What are parameters?

Parameters let you pass data into functions. Instead of hardcoding values, you make functions flexible to work with different inputs.

```python theme={null}
# Without parameters (inflexible)
def greet_alice():
    print("Hello, Alice!")

# With parameters (flexible)
def greet(name):
    print(f"Hello, {name}!")

# Now it works for anyone
greet("Alice")
greet("Bob")
greet("Charlie")
```

## Basic parameters

Add parameters inside the parentheses when defining a function:

```python theme={null}
def introduce(name, age):
    print(f"My name is {name}")
    print(f"I am {age} years old")

# Call with values
introduce("Alice", 25)
introduce("Bob", 30)
```

<Note>
  The values you pass when calling a function are called "arguments". The variables in the function definition are "parameters". Many people use these terms interchangeably.
</Note>

## Multiple parameters

Functions can have multiple parameters:

```python theme={null}
def calculate_total(price, tax_rate, discount):
    tax = price * tax_rate
    final_price = price + tax - discount
    print(f"Total: ${final_price}")

# Order matters!
calculate_total(100, 0.08, 10)  # $98
```

## Default values

Give parameters default values for optional arguments:

```python theme={null}
def greet(name, greeting="Hello"):
    print(f"{greeting}, {name}!")

# Use default
greet("Alice")           # Hello, Alice!

# Override default
greet("Bob", "Hi")       # Hi, Bob!
greet("Charlie", "Hey")  # Hey, Charlie!
```

<Tip>
  Put parameters with defaults at the end. Required parameters come first, optional ones last.
</Tip>

## Keyword arguments

Call functions using parameter names for clarity:

```python theme={null}
def create_profile(name, age, city):
    print(f"{name}, {age}, from {city}")

# Positional arguments (order matters)
create_profile("Alice", 25, "NYC")

# Keyword arguments (order doesn't matter)
create_profile(city="NYC", age=25, name="Alice")
create_profile(name="Bob", city="LA", age=30)
```

## Common mistakes

<AccordionGroup>
  <Accordion title="Wrong number of arguments">
    ```python theme={null}
    def greet(name, age):
        print(f"Hi {name}, you're {age}")

    # Wrong - too few arguments
    greet("Alice")  # TypeError!

    # Wrong - too many arguments
    greet("Alice", 25, "NYC")  # TypeError!

    # Right
    greet("Alice", 25)
    ```
  </Accordion>

  <Accordion title="Default values with mutable objects">
    ```python theme={null}
    # Wrong - don't use lists as defaults
    def add_item(item, list=[]):
        list.append(item)
        return list

    # Right - use None and create new list
    def add_item(item, list=None):
        if list is None:
            list = []
        list.append(item)
        return list
    ```
  </Accordion>
</AccordionGroup>

## What's next?

Functions become truly powerful when they can return values. Let's learn how!

<Card title="Return values" icon="arrow-right" href="/functions/return-values">
  Get results from functions
</Card>