Python Unpacking

1Python Unpacking: overview

Unpacking assigns the items of any iterable to several names in one statement, and a * lets one name collect the leftovers or spread items into a list, dictionary or function call.

Before this lesson: Python Lists, Python Tuples

2Python Unpacking: diagram

Quick reference: Python Unpacking

• How to Merge Two Dictionaries in Python — Use `merged = a | b` (Python 3.9+) or `merged = {**a, **b}` to merge two dictionaries into a new one. If both…
• How to Convert a Tuple to a List in Python — Use `list(my_tuple)`, for example `list((1, 2, 3))` returns `[1, 2, 3]`. The unpacking form `[*my_tuple]` doe…
• Python divmod() Function — `divmod(a, b)` returns the tuple `(a // b, a % b)`: the floor quotient and the remainder from a single divisi…
• Python String partition() Method — `str.partition(sep)` splits a string at the **first** occurrence of `sep` and always returns a tuple of three…

4Python Unpacking: syntax

a, b = [1, 2]                  # one name per item
first, *rest = items           # rest is always a list
*start, last = items           # star can come first, middle or last
first, *_, last = items        # _ = a value you ignore
(x, y), z = (1, 2), 3          # nested pattern
a, b = b, a                    # swap
for key, value in d.items():   # unpack in a loop
func(*args, **kwargs)          # spread into a call
new_list = [*a, *b]            # merge lists
new_dict = {**a, **b}          # merge dicts (later wins)

5Python Unpacking: run the example

Press Run (or Ctrl + Enter). The output (step 6) appears directly below the code. Change anything and run it again.

line = "Asha,Pune,82,91,77"
name, city, *marks = line.split(",")
marks = [int(m) for m in marks]
best, *rest = sorted(marks, reverse=True)
print(name, "from", city)
print("Best mark:", best, "| others:", rest)

profile = {"name": name, "city": city}
defaults = {"city": "unknown", "active": True}
merged = {**defaults, **profile}
print(merged)

def greet(name, city):
    return f"Hello {name} from {city}!"
print(greet(**profile))

Expected outputAsha from Pune
Best mark: 91 | others: [82, 77]
{'city': 'Pune', 'active': True, 'name': 'Asha'}
Hello Asha from Pune!

7Python Unpacking: how the example works

Hover or tap a step to highlight its lines in the example above.

1. Line 1A line of comma-separated text: a name, a city and three marks.
2. Line 2split(",") returns a list of five strings. name and city take the first two, and *marks collects the remaining three as a list: ['82', '91', '77'].
3. Line 3The marks are still text, so a list comprehension turns each one into an int.
4. Line 4sorted(..., reverse=True) gives [91, 82, 77]. The first value goes to best and *rest collects [82, 77].
5. Line 5-6Printing shows the pieces: Asha from Pune and the best mark with the others.
6. Line 8A small dictionary built from the variables we just unpacked.
7. Line 9-10{**defaults, **profile} pours both dictionaries into a new one. profile comes last, so its "city" replaces the default and "name" is added. The original dictionaries are not changed.
8. Line 11The merged dictionary keeps the key order of defaults first, then any new keys: city, active, name.
9. Line 13-14A function with two parameters named name and city.
10. Line 15greet(**profile) turns each key into a keyword argument, so it is the same as greet(name="Asha", city="Pune"). This only works because the keys match the parameter names.

8Python Unpacking: common mistakes

point = (3, 5, 7)
x, y = point

point = (3, 5, 7)
x, y, z = point
print(x, y, z)

x, y, *_ = point
print(x, y)

stock = {"pear": 3, "plum": 7}
for fruit, count in stock:
    print(fruit, count)

stock = {"pear": 3, "plum": 7}
for fruit, count in stock.items():
    print(fruit, count)

*head, *tail = [1, 2, 3, 4]

head, *tail = [1, 2, 3, 4]
print(head, tail)

def greet(name, city):
    return f"Hello {name} from {city}!"

profile = {"name": "Asha", "town": "Pune"}
print(greet(**profile))

def greet(name, city):
    return f"Hello {name} from {city}!"

profile = {"name": "Asha", "city": "Pune"}
print(greet(**profile))

a = 1
b = 2
a = b
b = a
print(a, b)

a = 1
b = 2
a, b = b, a
print(a, b)

9Python Unpacking: exercises

Write your answer, then press Check. The checks run in your browser.

record = ["Asha", "Pune", 28]
date = "2025-03-14"
low, high = 9, 3

# your code here

record = ["Asha", "Pune", 28]
date = "2025-03-14"
low, high = 9, 3

name, city, age = record
year, month, day = date.split("-")
low, high = high, low
print(name, year)

a, *b = "hello"
print(a, b)

x, (y, z), *w = 1, (2, 3), 4, 5
print(x, y, z, w)

first, *_, last = range(5)
print(first, last)

p, q = 1, 2
p, q = q, p + q
print(p, q)

h ['e', 'l', 'l', 'o']
1 2 3 [4, 5]
0 4
2 3

2 more exercises → 6 more examples

Further reading

• Data structures tutorial
• Sequence types: list, tuple, range
• collections module

10Next lesson

Related:
Python enumerate() and zip()Python TuplesPython DictionariesPython *args and **kwargs

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