Improve Python stdio handling and logging on Darwin

Clarifies in the README that Python stdout/stderr is forwarded via NSLog for better visibility. In the Swift plugin, ensures Python stdio is line-buffered for prompt log output and uses NSLog in addition to os_log for maximum log visibility in Xcode and log stream.

Author: FeodorFitsner

src/serious_python/README.md

@@ -183,7 +183,7 @@ dart run serious_python:main package app/src -p Darwin --verbose
 
 ### iOS/macOS Python output
 
-On Darwin (iOS/macOS), Python `stdout`/`stderr` is forwarded into Apple’s unified logging, so it’s visible in `flutter run` and Xcode logs.
+On Darwin (iOS/macOS), Python `stdout`/`stderr` is forwarded into Apple’s unified logging (via `NSLog`), so it’s visible in `flutter run` and Xcode logs.
 
 To disable forwarding, set `SERIOUS_PYTHON_FORWARD_STDIO=0` in `environmentVariables`.
 

src/serious_python_darwin/darwin/Classes/SeriousPythonPlugin.swift

@@ -116,6 +116,7 @@ public class SeriousPythonPlugin: NSObject, FlutterPlugin {
     @objc func runPythonFile(appPath: String) {
         SeriousPythonLogForwarder.shared.beginCapturing()
         Py_Initialize()
+        _configurePythonStdioLineBuffering()
 
         // run app
         let file = fopen(appPath, "r")
@@ -131,6 +132,7 @@ public class SeriousPythonPlugin: NSObject, FlutterPlugin {
     @objc func runPythonScript(script: String) {
         SeriousPythonLogForwarder.shared.beginCapturing()
         Py_Initialize()
+        _configurePythonStdioLineBuffering()
 
         // run app
         let result = PyRun_SimpleString(script)
@@ -141,6 +143,23 @@ public class SeriousPythonPlugin: NSObject, FlutterPlugin {
         Py_Finalize()
         SeriousPythonLogForwarder.shared.endCapturing()
     }
+    
+    private func _configurePythonStdioLineBuffering() {
+        // Best-effort: make print()/logging visible promptly when stdout/stderr is a pipe.
+        // Safe to ignore failures across Python versions/configs.
+        let code = """
+        import sys
+        try:
+            sys.stdout.reconfigure(line_buffering=True)
+        except Exception:
+            pass
+        try:
+            sys.stderr.reconfigure(line_buffering=True)
+        except Exception:
+            pass
+        """
+        _ = PyRun_SimpleString(code)
+    }
 }
 
 private final class SeriousPythonLogForwarder {
@@ -277,6 +296,8 @@ private final class SeriousPythonLogForwarder {
     private func _emit(_ message: String) {
         let trimmed = message.trimmingCharacters(in: .newlines)
         guard !trimmed.isEmpty else { return }
+        // Use NSLog for maximum visibility in Xcode + `log stream` by process.
+        NSLog("%@", trimmed)
         os_log("%{public}@", log: log, type: .default, trimmed)
     }
 }