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Python dict methods you actually use

Summary

Python dicts map keys to values and, since Python 3.7, keep insertion order. Use d.get(k, default) to read a key without risking a KeyError, setdefault to read or insert, pop and popitem to remove, and update or the | operator (3.9+) to merge. keys(), values() and items() return live views.

Draft. License: CC BY 4.0 (this summary). Sources: [S1] Python Software Foundation, "Mapping Types: dict (Python 3 docs)" (PSF License 2.0 docs; restated in our own words, no copied text).

Example

prices = {"apple": 1.2}
prices.get("pear", 0)          # 0, no KeyError
prices.setdefault("pear", 0.8)  # inserts pear
merged = prices | {"apple": 1.0}  # 3.9+
for k, v in prices.items():
    print(k, v)

Facts

• id: F1 claim: d[key] raises KeyError if the key is missing; d.get(key, default) returns default (None if omitted) instead and does not insert the key. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F2 claim: d.setdefault(key, default) returns the value if key exists; otherwise it inserts key with default and returns default. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F3 claim: d.pop(key[, default]) removes and returns the value; without a default it raises KeyError for a missing key. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F4 claim: d.popitem() removes and returns a (key, value) pair in LIFO order (guaranteed since 3.7); it raises KeyError on an empty dict. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F5 claim: Dictionaries preserve insertion order, a language guarantee since Python 3.7. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F6 claim: keys(), values() and items() return view objects that reflect later changes to the dict. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F7 claim: d1 | d2 (Python 3.9+) returns a new merged dict with d2's values winning on shared keys; d1 |= d2 updates in place, like d1.update(d2). confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F8 claim: dict.fromkeys(iterable, value) gives every key the same value object, so a mutable value such as a list is shared across all keys. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02
• id: F9 claim: Keys must be hashable; lists cannot be keys, tuples of hashable items can. confidence: medium date: 2026-11-02 sources: [S1] license: CC BY 4.0 checked_on: 2026-11-02

Caveats

• For counting or grouping, collections.Counter and collections.defaultdict are often cleaner.

Pointers

• id: P1 answers: Full details and updates where: https://docs.python.org/3/library/stdtypes.html#mapping-types-dict access: free, public web page

@misc{iil_note_2shj751x,
  author = {{iinventedlight Library}},
  title = {{Python dict methods you actually use}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-02},
  url = {https://iinventedlight.com/library/reference/python-docs/python-dict-methods/},
  note = {Permanent ID iil:note:2shj751x. License: CC-BY-4.0. Summary of https://docs.python.org/3/library/stdtypes.html\#mapping-types-dict.},
}

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