Iterating over dictionaries

Keys, values and both

Three views onto a dictionary:

for key in scores:              # keys — the default
for value in scores.values():   # values
for key, value in scores.items():   # both

.items() is the one you will use most. Since Python 3.7 dictionaries keep insertion order, so iteration is predictable.

in checks for a key, not a value:

"Ada" in scores          # True if Ada is a key
90 in scores.values()    # check the values instead

Your turn: write best(scores) returning the name with the highest score. If the dictionary is empty, return None.

Transforming a dictionary

Dictionary comprehensions work just like list comprehensions, with a key: value pair at the front:

doubled = {k: v * 2 for k, v in scores.items()}

Your turn: write passing(scores) returning a new dictionary containing only the entries scoring 50 or more. Leave the original untouched.