Dictionaries

Dictionaries

A Python dictionary stores key-value pairs. Keys must be hashable (strings, numbers, tuples). Dictionaries preserve insertion order since Python 3.7.

Creating and Accessing

person = {"name": "Alice", "age": 30}
person["name"]          # "Alice"
person.get("age")       # 30
person.get("email", "") # "" (default if missing)

Mutating

person["email"] = "alice@example.com"  # add/update
del person["age"]                       # delete key

Iterating

for key in person:              # iterate keys
for key, val in person.items(): # iterate pairs
for val in person.values():     # iterate values

Useful Methods

person.keys()    # dict_keys(['name', 'email'])
person.values()  # dict_values(['Alice', 'alice@...'])
person.items()   # dict_items([('name', 'Alice'), ...])
"name" in person # True

setdefault and defaultdict

d = {}
d.setdefault("count", 0)  # set only if missing
d["count"] += 1

Your Task

Implement word_count(text) that returns a dictionary mapping each word to how many times it appears in text. Words are separated by spaces; treat them case-insensitively (lowercase all words).