Dictionary
Create
| What | How | Details |
| Empty | x = {} | |
| Define with string keys | x = {'color': 'blue', 'size': 'large'} | |
| Define from keys (iterator) and constant value v | dict.fromkeys(key_iter, v) | |
| Define dynamically from iterators for keys and values | x = dict(zip(key_iter, value_iter)) | |
| Merge dictionaries | z = x | y | |
| Merge dictionaries | z = {**x, **y} | ? |
Get
| What | How | Details |
| Value | x['color'] | Throws an error if missing |
| Try get value | x.get('color') | Returns None if missing |
| Try get value with default v | x.get('color', v) | |
| Values from list of keys | [x[k] for k in keys_list] | |
| Keys (as dict_keys) | x.keys() | |
| Keys as list | list(x) | |
| Keys as sorted list | sorted(x) | |
| Values (as dict_values) | x.values() | |
| Values as list | list(x.values()) | |
| Values sorted by keys | [x[k] for k in sorted(x)] | |
| Entries (as list of tuples) | x.items() | |
| First key with value v | next(k for k in x if x[k] == v) | |
| All keys with value v | [k for k in x if x[k] == v] | |
Test
| What | How | Details |
| Empty | if x: | |
| Not empty | if not x: | |
| Contains key k | k in x | |
| Contains value v | v in x.values() | |
| Contains specific keys | {k1, k2}.issubset(x) | |
| Contains specific values | {v1, v2}.issubset(x.values()) | |
| Contains keys keys | set(keys).issubset(x) | |
| Contains values values | set(values).issubset(x.values()) | |
| Contains duplicate values | len(x) != len(set(x.values())) | |
Update
| What | How | Details |
| Set default entry value for missing key | x.setdefault('size', 'medium') | |
| Update entry value | x['size'] = 'small' | |
| Update entry, error if missing | ? | |
Grow
| What | How | Details |
| Add/update entry | x['size'] = 'small' | |
| Merge with another dictionary | x |= y | |
| Merge with another dictionary | x.update(y) | |
Shrink
| What | How | Details |
| Remove key | del x['size'] | |
| Remove keys | for k in keys: del x[k] | |
| Remove key, get value | x.pop('size') | |
| Remove keys, get values | [x.pop(k) for k in keys] | |
| Remove last item, get value | x.popitem() | |
| Clear | x.clear() | |
Derive
| What | How | Details |
| Copy | x.copy() | |
| Copy | dict(x) | ? |
| Subset for keys | {k: x[k] for k in keys} | Error if a key is missing |
| Subset for keys with default v | {k: x.get(k, default=v) for k in keys} | |
| Subset (intersection) for keys | {k: x[k] for k in x.keys() if k in keys} | Returns empty dict if all keys are missing |
| Subset except for keys | {k: x[k] for k in x.keys() if k not in keys} | |
Convert
| What | How | Details |
| Pretty print | pprint.pprint(x) | |
| List of key-value tuples | x.items() | |
| JSON string | json.dumps(x) | |
| JSON string, handle non-string entries | json.dumps(x, default = str) | |