pythonnative/src/pythonnative/_ios_log.py at main · pythonnative/pythonnative · GitHub

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"""Route Python `sys.stdout`/`sys.stderr` through fd 2 on iOS.

When an app is launched via `xcrun simctl launch --console-pty`

(what `pn run ios` does), the simulator attaches the caller's

terminal to the app's stderr, which is the same channel `NSLog` and

`os_log` write to. Python `print()` calls, however, go to

`sys.stdout` (fd 1), and for reasons specific to how CPython's

embedded framework is started on the iOS Simulator that descriptor

does not reach the attached console. As a result, users see

Swift-side `NSLog` output but never their own `print()` output.

Redirecting `sys.stdout` and `sys.stderr` at a Python level to write

straight to fd 2 is a small, reliable fix: fd 2 *is* visible to

`simctl` (that is exactly how `NSLog` reaches the terminal), so

Python output lands next to the Swift logs with correct ordering.

This module is intentionally self-contained (no bridge or

platform-specific C bindings required), so it is safe to import

early during `pythonnative` package initialization.

"""

from __future__ import annotations

import os

import sys

from typing import Iterable

_STDERR_FD = 2

class _StderrStream:

"""Minimal text-mode file-like that writes UTF-8 bytes to fd 2.

Write-through (no buffering), so a `print()` call appears in the

terminal immediately. That matches user expectations for an

interactive "run on simulator" log stream.

"""

encoding = "utf-8"

errors = "replace"

mode = "w"

name = "<stderr>"

def write(self, s: str) -> int:

if not s:

return 0

data = s.encode(self.encoding, self.errors)

try:

return os.write(_STDERR_FD, data)

except OSError:

return 0

def writelines(self, lines: Iterable[str]) -> None:

for line in lines:

self.write(line)

def flush(self) -> None:

# os.write is unbuffered; nothing to flush.

return None

def isatty(self) -> bool:

try:

return os.isatty(_STDERR_FD)

except OSError:

return False

def fileno(self) -> int:

return _STDERR_FD

def close(self) -> None:

# Don't actually close fd 2.

return None

@property

def closed(self) -> bool:

return False

_installed = False

def install() -> None:

"""Swap `sys.stdout` and `sys.stderr` for fd-2 writers.

Idempotent: only the first call has effect.

"""

global _installed

if _installed:

return

sys.stdout = _StderrStream()

sys.stderr = _StderrStream()

_installed = True

pythonnative/src/pythonnative/_ios_log.py at main · pythonnative/pythonnative · GitHub

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