Need to find a task’s urgency from its title? Use a Python dictionary, or `dict`, to store title–urgency pairs. Unlike a list or tuple, which holds individual items, a dictionary stores keys with corresponding values. The key gives you a way to retrieve the value. section 3.4
Look up task urgency
```python urgencies = {"Laundry": 3, "Homework": 5, "Museum": 2} print(urgencies["Homework"]) ``` Output: `5`. Use subscripting when you created the dictionary and want a misspelled key to surface as an error. For a dictionary supplied by someone else, `get` retrieves an item without raising `KeyError` when the key is absent. section 3.4 section 3.7
Choose a construction pattern that matches the data you already have:
- Use `dict(zip(id_numbers, titles))` for parallel iterables. `zip` supplies two-item pairs; `dict` takes the first item of each pair as a key and the second as its value. section 5.1.3
- Use `{task.title: task.description for task in tasks}` when each existing item supplies both parts. A dictionary comprehension makes that transformation concise. section 5.2.2
- Use dictionary views when accessing all keys, values, or pairs; the views stay in sync with their dictionary. section 3.7
Keys must be hashable: a list used as a key raises `TypeError`. Dictionaries and sets use hash tables, making item lookup efficient at O(1) time complexity. A dictionary cannot retain duplicate keys; when constructing one with repeated keys, the later value overrides the earlier value. section 3.5 section 3.5.3 section 3.5.4
Replace branches with a function lookup
```python actions = {"mean": get_mean, "min": get_min, "max": get_max} calculation = actions.get(action, fallback_action) processed = calculation(data) ``` Here the values are functions. Looking up the requested action avoids a growing `if`/`elif` chain, while `get` supplies a fallback for an unknown action. section 7.2.1
A dictionary can also label fields: `csv.DictReader` reads a CSV header as keys and produces a dictionary for each subsequent row. For a lightweight record, those keys make fields clearer than list positions, though mistyping a key can cause `KeyError`. section 11.2.2 section 3.3.1
