Dict Iteration and Tuples

Looping over a dict

Data travels in pairs and small fixed groups constantly: a point's (x, y), a row's (name, score), and every entry of a dict. This lesson covers the loop that processes a whole dict and the tuple, Python's type for those fixed little groups, together, because dict iteration hands you tuples.

Three views of a dictionary, three loops:

for name in ages:                 # keys (the default)
for age in ages.values():         # values only
for name, age in ages.items():    # pairs: the one you will use most

That two-variable form works because .items() hands out each pair as a tuple.

Tuples: sequences that never change

A tuple is written with parentheses: point = (3, 4). Index and slice it like a list, but it is immutable: point[0] = 9 is a TypeError. Use tuples for small fixed records where each position means something, like (x, y) or (name, score).

Unpacking splits a tuple into variables in one line, and it is why the .items() loop reads so well:

x, y = (3, 4)     # x is 3, y is 4
a, b = b, a       # the classic swap, no temp variable