test suite characterizing dict.get() (#13225)

stdlib/@tests/test_cases/builtins/check_dict.py

@@ -1,6 +1,6 @@
 from __future__ import annotations
 
-from typing import Dict, Generic, Iterable, TypeVar
+from typing import Any, Dict, Generic, Iterable, TypeVar, Union
 from typing_extensions import assert_type
 
 # These do follow `__init__` overloads order:
@@ -57,3 +57,93 @@ assert_type(dict(string.split(b".") for string in i4), Dict[bytes, bytes])
 
 dict(["foo", "bar", "baz"])  # type: ignore
 dict([b"foo", b"bar", b"baz"])  # type: ignore
+
+# Exploring corner cases of dict.get()
+d_any: dict[str, Any] = {}
+d_str: dict[str, str] = {}
+any_value: Any = None
+str_value = "value"
+int_value = 1
+
+assert_type(d_any["key"], Any)
+assert_type(d_any.get("key"), Union[Any, None])
+assert_type(d_any.get("key", None), Any)
+assert_type(d_any.get("key", any_value), Any)
+assert_type(d_any.get("key", str_value), Any)
+assert_type(d_any.get("key", int_value), Any)
+
+assert_type(d_str["key"], str)
+assert_type(d_str.get("key"), Union[str, None])
+assert_type(d_str.get("key", None), Union[str, None])
+# Pyright has str instead of Any here
+assert_type(d_str.get("key", any_value), Any)  # pyright: ignore[reportAssertTypeFailure]
+assert_type(d_str.get("key", str_value), str)
+assert_type(d_str.get("key", int_value), Union[str, int])
+
+# Now with context!
+result: str
+result = d_any["key"]
+result = d_any.get("key")  # type: ignore[assignment]
+result = d_any.get("key", None)
+result = d_any.get("key", any_value)
+result = d_any.get("key", str_value)
+result = d_any.get("key", int_value)
+
+result = d_str["key"]
+result = d_str.get("key")  # type: ignore[assignment]
+result = d_str.get("key", None)  # type: ignore[arg-type]
+result = d_str.get("key", any_value)
+result = d_str.get("key", str_value)
+result = d_str.get("key", int_value)  # type: ignore[arg-type]
+
+
+# Return values also make things weird
+
+# Pyright doesn't have a version of no-any-return,
+# and mypy doesn't have a type: ignore that pyright will ignore.
+# def test1() -> str:
+#     return d_any["key"]  # mypy: ignore[no-any-return]
+
+
+def test2() -> str:
+    return d_any.get("key")  # type: ignore[return-value]
+
+
+# def test3() -> str:
+#     return d_any.get("key", None)  # mypy: ignore[no-any-return]
+#
+#
+# def test4() -> str:
+#     return d_any.get("key", any_value)  # mypy: ignore[no-any-return]
+#
+#
+# def test5() -> str:
+#     return d_any.get("key", str_value)  # mypy: ignore[no-any-return]
+#
+#
+# def test6() -> str:
+#     return d_any.get("key", int_value)  # mypy: ignore[no-any-return]
+
+
+def test7() -> str:
+    return d_str["key"]
+
+
+def test8() -> str:
+    return d_str.get("key")  # type: ignore[return-value]
+
+
+def test9() -> str:
+    return d_str.get("key", None)  # type: ignore[arg-type]
+
+
+def test10() -> str:
+    return d_str.get("key", any_value)
+
+
+def test11() -> str:
+    return d_str.get("key", str_value)
+
+
+def test12() -> str:
+    return d_str.get("key", int_value)  # type: ignore[arg-type]