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typeddict: clarify that .get() with an unknown literal key is not an error by ashishpatel26 · Pull Request #2312 · python/typing · GitHub

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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 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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Original file line number Diff line number Diff line change
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 Jun 23, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

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 Jun 23, 2026

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Choose a reason Spam Abuse Off Topic Outdated Duplicate Resolved Low Quality

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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