Data unpacking

Extract values from a sequence into separate named variables for clearer code.

Python: swapping two values without a temporary variable; Python: splitting a pair or tuple into individual variables; Python: iterating over pairs in a loop

Common in Python scripts, data processing pipelines, loops over enumerated items, and functions returning multiple values.

first_var, second_var = iterable

... , ... = ...

first_var: identifier, second_var: identifier, iterable: expression yielding at least two items

• swapping values
• loop iteration
• function returns with multiple values

• Extended unpacking with star
• e.g.
• a
• *rest = t
• using indexing like a = t[0]
• b = t[1]

Mismatched number of variables and iterable length causing ValueError; assuming unpacking works with non-iterable objects; forgetting parentheses when needed.

Sequential assignment (a = t[0]; b = t[1]) – more explicit but verbose; attribute unpacking like obj.x, obj.y = t – assigns to attributes instead of variables.

Coming from Java: may try to assign via temporary variable → use tuple unpacking a, b = t

• tuple unpacking
• sequence unpacking
• parallel assignment

Do not use when the iterable length may not match the number of variables unless using star unpacking, as it raises ValueError; performance impact is minimal—just O(n) iteration with no extra copying; note that the right side is evaluated first, enabling swaps, and generators are exhausted after unpacking.

Makes code more readable and avoids indexing errors; enables idiomatic swaps and clear multiple return value handling.

Think of unpacking a suitcase: pull out each item into its own slot.

Use parentheses when unpacking in return statements or when ambiguity may arise; otherwise parentheses are optional.

a, *rest = t (extended unpacking)