Python dictionaries are accessed by key, not offset position.
The following table summarizes some of the most common and representative dictionary operations.
| Operation | Interpretation |
|---|---|
| D = {} | Empty dictionary |
| D = {'name': 'test', 'age': 40} | Two-item dictionary |
| E = {'cto': {'name': 'test', 'age': 40}} | Nesting |
| D = dict(name='test', age=40) | Alternative construction techniques: |
| D = dict([('name', 'test'), ('age', 40)]) D = dict(zip(keyslist, valueslist)) D = dict.fromkeys(['name', 'age']) | keywords, key/value pairs, zipped key/value pairs, key lists |
| D['name'] E['cto']['age'] | Indexing by key |
| 'age' in D | Membership: key present test |
| D.keys() | Methods: all keys, |
| D.values() | all values, |
| D.items() | all key+value tuples, |
| D.copy() | copy (top-level), |
| D.clear() | clear (remove all items), |
| D.update(D2) | merge by keys, |
| D.get(key, default?) | fetch by key, if absent default (or None), |
| D.pop(key, default?) | remove by key, if absent default (or error) |
| D.setdefault(key, default?) | fetch by key, if absent set default (or None), |
| D.popitem() | remove/return any (key, value) pair; etc. |
| len(D) | Length: number of stored entries |
| D[key] = 42 | Adding/changing keys |
| del D[key] | Deleting entries by key |
| list(D.keys()) D1.keys() & D2.keys() | Dictionary views (Python 3.X) |
| D.viewkeys(), D.viewvalues() | Dictionary views (Python 2.7) |
| D = {x: x*2 for x in range(10)} | Dictionary comprehensions (Python 3.X, 2.7) |