Functions, args, kwargs, defaults

def name(params): ... return value. *args collects positional, **kwargs collects keyword.

script.py v3.1

def greet(name, greeting='Hello', shout=False):
    msg = f'{greeting}, {name}!'
    if shout:
        msg = msg.upper()
    return msg

# Positional args
print(greet('Ada'))

# Keyword args (order doesn't matter)
print(greet(greeting='Hi', name='Alan'))

# Default arg used
print(greet('Bob', shout=True))

# *args — collect extra positional into a tuple
def sum_all(*nums):
    return sum(nums)
print('sum:', sum_all(1, 2, 3, 4, 5))

# **kwargs — collect extra keyword into a dict
def show_config(**opts):
    for k, v in opts.items():
        print(f'  {k}: {v}')
show_config(debug=True, port=8080, host='localhost')

Python output click Run to execute

Click "Run" to execute the code on the left.
The output will appear here.

🧠 How it works

def name(params): body return value. Default args use '=' — evaluated ONCE at def time (mutable defaults like def f(x=[]) are a famous footgun!). *args collects extra positional args into a tuple. **kwargs collects extra keyword args into a dict. Order: positional, *args, keyword-only, **kwargs. Passing *list and **dict unpacks them into separate args: f(*[1,2,3]) is f(1, 2, 3). Functions are first-class — you can pass them as args, return them, store in variables.

✏️ Try these changes

Change greeting='Hello' to greeting='Hi'
→ default greeting changes
Add a new parameter punctuation='!' and append it to msg
→ greeting ends with the punctuation
Change sum_all(1,2,3,4,5) to sum_all(*range(1, 6))
→ unpacks range into args — same result
Call greet() with no args
→ TypeError — name is required

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