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typeddict: clarify that .get() with an unknown literal key is not an error #2312

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typeddict: clarify that .get() with an unknown literal key is not an …
ashishpatel26 Jun 22, 2026
6313c8e
conformance: fix zuban line number and update results.html for pycros…
ashishpatel26 Jun 22, 2026
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6 changes: 3 additions & 3 deletions conformance/results/mypy/typeddicts_operations.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -8,9 +8,9 @@ typeddicts_operations.py:28: error: Missing key "year" for TypedDict "Movie" [t
typeddicts_operations.py:29: error: Incompatible types (expression has type "float", TypedDict item "year" has type "int") [typeddict-item]
typeddicts_operations.py:32: error: Extra key "other" for TypedDict "Movie" [typeddict-unknown-key]
typeddicts_operations.py:37: error: Expected TypedDict key to be string literal [misc]
typeddicts_operations.py:47: error: "Movie" has no attribute "clear" [attr-defined]
typeddicts_operations.py:49: error: Key "name" of TypedDict "Movie" cannot be deleted [misc]
typeddicts_operations.py:62: error: "MovieOptional" has no attribute "clear" [attr-defined]
typeddicts_operations.py:49: error: "Movie" has no attribute "clear" [attr-defined]
typeddicts_operations.py:51: error: Key "name" of TypedDict "Movie" cannot be deleted [misc]
typeddicts_operations.py:64: error: "MovieOptional" has no attribute "clear" [attr-defined]
"""
conformance_automated = "Pass"
errors_diff = """
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16 changes: 11 additions & 5 deletions conformance/results/pycroscope/typeddicts_operations.toml
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Original file line number Diff line number Diff line change
@@ -1,5 +1,11 @@
conformance_automated = "Pass"
conformant = "Partial"
notes = """
Incorrectly flags ``TypedDict.get()`` with an unknown literal string key as an
error; the spec requires this to be allowed.
"""
conformance_automated = "Fail"
errors_diff = """
Line 46: Unexpected errors ["./typeddicts_operations.py:46:0: Unknown TypedDict key 'other' [invalid_typeddict_key]"]
"""
output = """
./typeddicts_operations.py:22:0: Value for key 'name' must be str, not Literal[1982] [incompatible_argument]
Expand All @@ -10,8 +16,8 @@ output = """
./typeddicts_operations.py:29:0: Incompatible assignment: expected TypedDict({"name": str, "year": int}), got Literal[{'name': 'Blade Runner', 'year': 1982.1}] [incompatible_assignment]
./typeddicts_operations.py:32:0: Incompatible assignment: expected TypedDict({"name": str, "year": int}), got Literal[{'name': '', 'year': 1900, 'other': 2}] [incompatible_assignment]
./typeddicts_operations.py:37:4: Incompatible assignment: expected TypedDict({"name": str, "year": int}), got <dict containing {str: Literal[''], Literal['year']: Literal[1900]}> [incompatible_assignment]
./typeddicts_operations.py:44:0: Unknown TypedDict key 'other' [invalid_typeddict_key]
./typeddicts_operations.py:47:0: Cannot call clear() on non-closed TypedDict [incompatible_call]
./typeddicts_operations.py:49:10: Cannot delete required TypedDict key Literal['name'] [incompatible_argument]
./typeddicts_operations.py:62:0: Cannot call clear() on non-closed TypedDict [incompatible_call]
./typeddicts_operations.py:46:0: Unknown TypedDict key 'other' [invalid_typeddict_key]
./typeddicts_operations.py:49:0: Cannot call clear() on non-closed TypedDict [incompatible_call]
./typeddicts_operations.py:51:10: Cannot delete required TypedDict key Literal['name'] [incompatible_argument]
./typeddicts_operations.py:64:0: Cannot call clear() on non-closed TypedDict [incompatible_call]
"""
6 changes: 3 additions & 3 deletions conformance/results/pyrefly/typeddicts_operations.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -12,7 +12,7 @@ ERROR typeddicts_operations.py:29:42-48: `float` is not assignable to TypedDict
ERROR typeddicts_operations.py:32:36-43: Key `other` is not defined in TypedDict `Movie` [bad-typed-dict-key]
ERROR typeddicts_operations.py:37:20-52: Missing required key `name` for TypedDict `Movie` [bad-typed-dict-key]
ERROR typeddicts_operations.py:37:21-33: Expected string literal key, got `str` [bad-typed-dict-key]
ERROR typeddicts_operations.py:47:1-12: Object of class `Movie` has no attribute `clear` [missing-attribute]
ERROR typeddicts_operations.py:49:11-17: Key `name` in TypedDict `Movie` may not be deleted [unsupported-delete]
ERROR typeddicts_operations.py:62:1-21: Object of class `MovieOptional` has no attribute `clear` [missing-attribute]
ERROR typeddicts_operations.py:49:1-12: Object of class `Movie` has no attribute `clear` [missing-attribute]
ERROR typeddicts_operations.py:51:11-17: Key `name` in TypedDict `Movie` may not be deleted [unsupported-delete]
ERROR typeddicts_operations.py:64:1-21: Object of class `MovieOptional` has no attribute `clear` [missing-attribute]
"""
6 changes: 3 additions & 3 deletions conformance/results/pyright/typeddicts_operations.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -15,11 +15,11 @@ typeddicts_operations.py:29:42 - error: Type "dict[str, str | float]" is not ass
typeddicts_operations.py:32:36 - error: Type "dict[str, str | int]" is not assignable to declared type "Movie"
  "other" is an undefined item in type "Movie" (reportAssignmentType)
typeddicts_operations.py:37:20 - error: Type "dict[str, str | int]" is not assignable to declared type "Movie" (reportAssignmentType)
typeddicts_operations.py:47:7 - error: Cannot access attribute "clear" for class "Movie"
typeddicts_operations.py:49:7 - error: Cannot access attribute "clear" for class "Movie"
  Attribute "clear" is unknown (reportAttributeAccessIssue)
typeddicts_operations.py:49:5 - error: Could not delete item in TypedDict
typeddicts_operations.py:51:5 - error: Could not delete item in TypedDict
  "name" is a required key and cannot be deleted (reportGeneralTypeIssues)
typeddicts_operations.py:62:16 - error: Cannot access attribute "clear" for class "MovieOptional"
typeddicts_operations.py:64:16 - error: Cannot access attribute "clear" for class "MovieOptional"
  Attribute "clear" is unknown (reportAttributeAccessIssue)
"""
conformance_automated = "Pass"
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12 changes: 9 additions & 3 deletions conformance/results/results.html
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6 changes: 3 additions & 3 deletions conformance/results/ty/typeddicts_operations.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ typeddicts_operations.py:28:9: error[missing-typed-dict-key] Missing required ke
typeddicts_operations.py:29:42: error[invalid-argument-type] Invalid argument to key "year" with declared type `int` on TypedDict `Movie`: value of type `float`
typeddicts_operations.py:32:36: error[invalid-key] Unknown key "other" for TypedDict `Movie`
typeddicts_operations.py:37:20: error[missing-typed-dict-key] Missing required key 'name' in TypedDict `Movie` constructor
typeddicts_operations.py:47:1: error[unresolved-attribute] Object of type `Movie` has no attribute `clear`
typeddicts_operations.py:49:11: error[invalid-argument-type] Cannot delete required key "name" from TypedDict `Movie`
typeddicts_operations.py:62:1: error[unresolved-attribute] Object of type `MovieOptional` has no attribute `clear`
typeddicts_operations.py:49:1: error[unresolved-attribute] Object of type `Movie` has no attribute `clear`
typeddicts_operations.py:51:11: error[invalid-argument-type] Cannot delete required key "name" from TypedDict `Movie`
typeddicts_operations.py:64:1: error[unresolved-attribute] Object of type `MovieOptional` has no attribute `clear`
"""
6 changes: 3 additions & 3 deletions conformance/results/zuban/typeddicts_operations.toml
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Original file line number Diff line number Diff line change
Expand Up @@ -10,7 +10,7 @@ typeddicts_operations.py:28: error: Missing key "year" for TypedDict "Movie" [t
typeddicts_operations.py:29: error: Incompatible types (expression has type "float", TypedDict item "year" has type "int") [typeddict-item]
typeddicts_operations.py:32: error: Extra key "other" for TypedDict "Movie" [typeddict-unknown-key]
typeddicts_operations.py:37: error: Expected TypedDict key to be string literal [literal-required]
typeddicts_operations.py:47: error: "Movie" has no attribute "clear" [attr-defined]
typeddicts_operations.py:49: error: Key "name" of TypedDict "Movie" cannot be deleted [misc]
typeddicts_operations.py:62: error: "MovieOptional" has no attribute "clear" [attr-defined]
typeddicts_operations.py:49: error: "Movie" has no attribute "clear" [attr-defined]
typeddicts_operations.py:51: error: Key "name" of TypedDict "Movie" cannot be deleted [misc]
typeddicts_operations.py:64: error: "MovieOptional" has no attribute "clear" [attr-defined]
"""
8 changes: 5 additions & 3 deletions conformance/tests/typeddicts_operations.py
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Expand Up @@ -37,11 +37,13 @@ def func1(variable_key: str):
movie: Movie = {variable_key: "", "year": 1900} # E: variable key


# It's not clear from the spec what type this should be.
# > For required keys, type checkers may return either the declared type T
# > or T | None.
movie.get("name")

# It's not clear from the spec what type this should be.
movie.get("other") # E?
# > If ``e`` is a string literal that is not a defined key of ``d``,
# > no error should be reported.
movie.get("other")


movie.clear() # E: clear not allowed
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16 changes: 13 additions & 3 deletions docs/spec/typeddict.rst
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Expand Up @@ -757,9 +757,19 @@ This section discusses some specific operations in more detail.
should be allowed for TypedDict objects, for an arbitrary expression
``e`` with type ``str``. The motivation is that these are safe and
can be useful for introspecting TypedDict objects. The static type
of ``d.get(e)`` should be the union of all possible item types in ``d``
if the string value of ``e`` cannot be determined statically.
(This simplifies to ``object`` if ``d`` is :term:`open`.)
of ``d.get(e)`` depends on what is known about the value of ``e``:

- If ``e`` is a string literal equal to a defined key of ``d``, the
return type is the declared type of that key combined with ``None``
for non-required keys. For required keys, type checkers may return
either the declared type ``T`` or ``T | None``.
Comment on lines +764 to +765

@JelleZijlstra JelleZijlstra Jun 23, 2026

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Why leave this as an option? If the key is required, then it must be present so .get() can't return None.

- If ``e`` is a string literal that is **not** a defined key of ``d``,
no error should be reported. The return type is the union of all
possible value types in ``d`` combined with ``None``.
- If the string value of ``e`` cannot be determined statically, the
return type is the union of all possible value types in ``d``
combined with ``None``. (This simplifies to ``object | None`` if

@JelleZijlstra JelleZijlstra Jun 23, 2026

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Which is just object.

``d`` is :term:`open`.)

* ``clear()`` is not safe on :term:`open` TypedDicts since it could remove required items, some of which
may not be directly visible because of :term:`structural`
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