What is a tuple in Python and when should you choose it over a list?

A tuple is an ordered, immutable sequence. Once created it cannot be changed — no appending, inserting, or item reassignment. The syntax uses parentheses (optional in many contexts) or just a comma: point = 3, 4 is a tuple.

coords = (40.7128, -74.0060)  # latitude, longitude
x, y   = coords               # tuple unpacking
print(x)   # 40.7128

# Single-element tuple needs a trailing comma
single = (42,)   # tuple
not_a_tuple = (42)  # just the int 42

# Tuples support indexing and slicing like lists
print(coords[0])   # 40.7128
print(coords[-1])  # -74.006

When should you choose a tuple over a list? Several rules of thumb:

• Immutability intent: if the data should not change after creation — RGB colour, (lat, lon), a database record — a tuple signals that clearly.
• Dictionary keys: only hashable (immutable) objects can be dict keys. A tuple of ints or strings is hashable; a list is not.
• Slight performance edge: tuples use less memory and are slightly faster to create than lists because Python can optimise their storage.
• Named tuples: collections.namedtuple adds field names to a tuple for readability without the overhead of a full class: Point = namedtuple('Point', ['x', 'y']).

A common interview trap: tuples are immutable, but a tuple can contain a mutable object like a list. The tuple itself cannot be changed, but the list inside it can.