simply use default arguments for stdout and stderr

Unless this runs me into the famous Python default argument folly, which doesn't seem likely to me, then this should be a better way to do it. (What, do we change sys.stdout during the course of the program? Guess CI will let me find out...)

On another note, sys.stdout and sys.strerr can themselves technically be None, and typeshed gives them MaybeNone to pay homage to this — I would like to actually handle this correctly in the mypy code here, but, what are you going to do, write a message to stderr about it? Guess we'll just roll on.

Author: wyattscarpenter

mypy/build.py

@@ -147,8 +147,8 @@ def build(
     alt_lib_path: str | None = None,
     flush_errors: Callable[[str | None, list[str], bool], None] | None = None,
     fscache: FileSystemCache | None = None,
-    stdout: TextIO | None = None,
-    stderr: TextIO | None = None,
+    stdout: TextIO = sys.stdout,
+    stderr: TextIO = sys.stderr,
     extra_plugins: Sequence[Plugin] | None = None,
 ) -> BuildResult:
     """Analyze a program.
@@ -183,8 +183,6 @@ def default_flush_errors(
         messages.extend(new_messages)
 
     flush_errors = flush_errors or default_flush_errors
-    stdout = stdout or sys.stdout
-    stderr = stderr or sys.stderr
     extra_plugins = extra_plugins or []
 
     try:

mypy/config_parser.py

@@ -314,17 +314,15 @@ def parse_config_file(
     options: Options,
     set_strict_flags: Callable[[], None],
     filename: str | None,
-    stdout: TextIO | None = None,
-    stderr: TextIO | None = None,
+    stdout: TextIO = sys.stdout,
+    stderr: TextIO = sys.stderr,
 ) -> None:
     """Parse a config file into an Options object.
 
     Errors are written to stderr but are not fatal.
 
     If filename is None, fall back to default config files.
     """
-    stdout = stdout or sys.stdout
-    stderr = stderr or sys.stderr
 
     ret = (
         _parse_individual_file(filename, stderr)

mypy/main.py

@@ -1337,8 +1337,8 @@ def add_invertible_flag(
 
 def process_options(
     args: list[str],
-    stdout: TextIO | None = None,
-    stderr: TextIO | None = None,
+    stdout: TextIO = sys.stdout,
+    stderr: TextIO = sys.stderr,
     require_targets: bool = True,
     server_options: bool = False,
     fscache: FileSystemCache | None = None,
@@ -1352,8 +1352,6 @@ def process_options(
 
     Returns a tuple of: a list of source files, an Options collected from flags.
     """
-    stdout = stdout if stdout is not None else sys.stdout
-    stderr = stderr if stderr is not None else sys.stderr
 
     parser, _, strict_flag_assignments = define_options(
         program, header, stdout, stderr, server_options