Parameters & Arguments

Functions become powerful when they can accept data. This is done using Parameters and Arguments.

• Parameter: The variable listed inside the parentheses in the function definition.
• Argument: The value that is sent to the function when it is called.

Positional Arguments

By default, arguments must be passed in the correct order.

Keyword Arguments

You can pass arguments by key=value syntax. In this case, the order doesn't matter.

Default Values

You can define a default value for a parameter. If the caller doesn't provide an argument, the default is used.

Advanced: Positional-Only and Keyword-Only Parameters ⚡

Python 3.8+ introduced special syntax to enforce how arguments can be passed.

Positional-Only (/)

Parameters before / MUST be passed positionally.

Keyword-Only (*)

Parameters after * MUST be passed as keywords.

Mutable Default Arguments Pitfall ⚠️

NEVER use mutable objects (like lists or dicts) as default values! They persist across function calls.

Unpacking Arguments with * and **

You can unpack lists and dictionaries when calling functions.

Coding Challenge: Flexible Greeting System 🎭

Create a function greet_user that:

• Takes a name (required)
• Takes a greeting (keyword-only, default "Hello")
• Takes any number of additional info items (*args)
• Prints a formatted greeting

Quiz

Key Takeaways

✅ Parameters define what data a function accepts.
✅ Arguments are the actual data passed.
✅ Use / for positional-only and * for keyword-only parameters.
✅ Never use mutable defaults ([], {}).
✅ Use * and ** to unpack arguments.

What's Next?

Now that we can send data in, let's learn how to get data out using Return Values.

Keep coding! 🚀