Fix _csv.Dialect.__init__ (#12320)

stdlib/@tests/stubtest_allowlists/common.txt

@@ -11,7 +11,6 @@ _collections_abc.AsyncGenerator.ag_running
 _collections_abc.ItemsView.__reversed__
 _collections_abc.KeysView.__reversed__
 _collections_abc.ValuesView.__reversed__
-_csv.Dialect.__init__  # C __init__ signature is inaccurate
 _ctypes.CFuncPtr  # stubtest erroneously thinks it can't be subclassed
 _threading_local.local.__new__
 ast.Bytes.__new__

stdlib/_csv.pyi

@@ -20,6 +20,8 @@ _QuotingType: TypeAlias = int
 
 class Error(Exception): ...
 
+_DialectLike: TypeAlias = str | Dialect | type[Dialect]
+
 class Dialect:
     delimiter: str
     quotechar: str | None
@@ -29,9 +31,18 @@ class Dialect:
     lineterminator: str
     quoting: _QuotingType
     strict: bool
-    def __init__(self) -> None: ...
-
-_DialectLike: TypeAlias = str | Dialect | type[Dialect]
+    def __init__(
+        self,
+        dialect: _DialectLike | None = ...,
+        delimiter: str = ",",
+        doublequote: bool = True,
+        escapechar: str | None = None,
+        lineterminator: str = "\r\n",
+        quotechar: str | None = '"',
+        quoting: _QuotingType = 0,
+        skipinitialspace: bool = False,
+        strict: bool = False,
+    ) -> None: ...
 
 class _reader(Iterator[list[str]]):
     @property

stdlib/csv.pyi

@@ -1,12 +1,10 @@
 import sys
-
-# actually csv.Dialect is a different class to _csv.Dialect at runtime, but for typing purposes, they're identical
 from _csv import (
     QUOTE_ALL as QUOTE_ALL,
     QUOTE_MINIMAL as QUOTE_MINIMAL,
     QUOTE_NONE as QUOTE_NONE,
     QUOTE_NONNUMERIC as QUOTE_NONNUMERIC,
-    Dialect as Dialect,
+    Dialect as _Dialect,
     Error as Error,
     __version__ as __version__,
     _DialectLike,
@@ -61,6 +59,9 @@ if sys.version_info < (3, 13):
 
 _T = TypeVar("_T")
 
+class Dialect(_Dialect):
+    def __init__(self) -> None: ...
+
 class excel(Dialect): ...
 class excel_tab(excel): ...
 class unix_dialect(Dialect): ...