feat(trace): live terminal output under bpython via a shared emit()

Live sniff/sim stream trace frames from a background thread. bpython replaces sys.stdout with a capture object whose write() does a greenlet switch back to the main thread — which raises off-thread; the text buffers but only repaints on the next keypress, so streamed frames 'pile up until you touch a key'. New trace/output.py emit() buffers via the repl's on_write and fires bpython's threadsafe repaint trigger; a plain write everywhere else, with a safe fallback on any internals mismatch.

Route TraceFormatter.print(), SimSession's sim-ended status, and SniffSession's state message through emit(). Flip the trace-line newline convention from leading to trailing so each emitted line self-terminates (format_sniff_line + test updated to match).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pm3py/sim/sim_session.py

@@ -12,6 +12,7 @@ from .frame import RFFrame
 from .table_compiler import ResponseTable, TableCompiler
 from pm3py.trace.format import TraceFormatter
 from pm3py.trace.decode_iso14a import decode_14443a
+from pm3py.trace.output import emit
 from .transponder import Transponder
 from ..core.protocol import Cmd
 from ..core.transport import encode_ng_frame, decode_response_frame, RESP_PREAMBLE_MAGIC, RESP_PREAMBLE_SIZE, RESP_POSTAMBLE_SIZE
@@ -394,7 +395,7 @@ class SimSession:
                             # HF_ISO14443A_SIMULATE (0x0384) but its teardown reply
                             # is HF_MIFARE_SIMULATE (0x0610) — watch for the latter.
                             self._active = False
-                            print(f"[SimSession] 14a sim ended, status={resp['status']}")
+                            emit(f"[SimSession] 14a sim ended, status={resp['status']}\n")
                             return
 
                         if resp["cmd"] in _TRACE_CMDS:

pm3py/sniff/session.py

@@ -1,6 +1,5 @@
 """Sniff sessions — live streaming with button-toggle, or legacy batch."""
 import struct
-import sys
 import threading
 import time
 
@@ -19,6 +18,7 @@ from ..core.transport import (
 from ..trace import parse_tracelog
 from ..trace.decode_iso15 import decode_15693
 from ..trace.format import TraceFormatter, format_sniff_line
+from ..trace.output import emit
 
 # Default serial port (same as SimSession)
 DEFAULT_PORT = "/dev/ttyACM0"
@@ -220,8 +220,7 @@ class SniffSession:
         count_str = f" ({count} frames)" if count > 0 else ""
 
         msg = f"\n[Snf] {icon} {label}{count_str}\n"
-        sys.stdout.write(msg)
-        sys.stdout.flush()
+        emit(msg)
 
         if state == SNIFF_STATE_STOPPED:
             self._active = False

pm3py/trace/format.py

@@ -6,6 +6,7 @@ import signal
 import sys
 
 from .decode_iso15 import decode_15693
+from .output import emit
 
 # ---- ANSI colors ----
 _C_CYAN = "\033[36m"
@@ -150,7 +151,7 @@ class TraceFormatter:
                 line = f"{prefix_colored}{hex_colored}{' ' * gap}{ann_colored}"
             else:
                 line = f"{prefix_colored}{hex_colored}"
-            return f"\n{line}"
+            return f"{line}\n"
 
         # Multi-line
         pad = " " * prefix_len
@@ -168,7 +169,7 @@ class TraceFormatter:
                 ann_pad = max(avail - len(al), 0)
                 parts.append(f"{pad}{' ' * ann_pad}{self._color(ann_color, al)}")
 
-        return "\n" + "\n".join(parts)
+        return "\n".join(parts) + "\n"
 
     def _color_hex_line(self, line: str, data_hex: str, crc_hex: str) -> str:
         if not crc_hex:
@@ -229,9 +230,8 @@ class TraceFormatter:
         return lines or [""]
 
     def print(self, direction: int, payload: bytes, crc_fail: bool = False) -> None:
-        """Format and print a trace line to stdout."""
-        sys.stdout.write(self.format(direction, payload, crc_fail=crc_fail))
-        sys.stdout.flush()
+        """Format and print a trace line, live even under bpython."""
+        emit(self.format(direction, payload, crc_fail=crc_fail))
 
 
 def format_sniff_line(entry: dict, width: int = 120, is_tty: bool = True) -> str:
@@ -243,5 +243,5 @@ def format_sniff_line(entry: dict, width: int = 120, is_tty: bool = True) -> str
                          width=width, is_tty=is_tty, crc_len=2)
     direction = 1 if entry["is_response"] else 0
     result = fmt.format(direction, entry["data"])
-    # Strip leading newline that TraceFormatter adds
-    return result.lstrip("\n")
+    # Strip the trailing newline that TraceFormatter adds
+    return result.rstrip("\n")

pm3py/trace/output.py

@@ -0,0 +1,75 @@
+"""Terminal output that stays live under interactive REPLs.
+
+Live sniff and sim stream trace frames from a background thread. Writing those
+straight to ``sys.stdout`` is fine in a plain REPL, but bpython replaces stdout
+with a capture object whose ``write`` hands control back to the main REPL thread
+via a greenlet switch — which raises from any other thread. The text is buffered
+first, so it survives, but the display only repaints on the next keypress, so
+streamed frames appear to "pile up until you touch a key".
+
+bpython exposes exactly the escape hatch we need: ``_interrupting_refresh_callback``
+is a curtsies ``threadsafe_event_trigger`` built to wake the input loop from
+another thread. So under bpython we buffer the text directly (via the repl's
+``on_write``, skipping the greenlet-switching ``write``) and then fire that
+trigger to force an immediate repaint. Everywhere else — plain python, IPython —
+it is just a direct write. All of the bpython plumbing is internal, so any
+mismatch falls back to a plain write and the sniff keeps working (just
+keypress-flushed) rather than breaking.
+
+The detection is intentionally bpython-only: the "wake the render loop" step is
+per-REPL and there is no universal hook, so we special-case the one REPL we use
+and let every other environment take the direct-write default.
+"""
+from __future__ import annotations
+
+import sys
+
+
+def _bpython_sink():
+    """Return ``(on_write, wake)`` for the running bpython repl, else ``None``.
+
+    ``sys.stdout`` under bpython is a ``FakeOutput`` whose ``on_write`` is a bound
+    method of the running repl; that repl carries the thread-safe repaint trigger.
+    Every access here is bpython-internal, so a miss just yields ``None``.
+    """
+    out = sys.stdout
+    if type(out).__module__.split(".", 1)[0] != "bpython":
+        return None
+    on_write = getattr(out, "on_write", None)
+    repl = getattr(on_write, "__self__", None)
+    wake = getattr(repl, "_interrupting_refresh_callback", None)
+    if callable(on_write) and callable(wake):
+        return on_write, wake
+    return None
+
+
+def emit(text: str) -> None:
+    """Write trace ``text`` to the terminal, live even under bpython.
+
+    Safe to call from a background thread. Under bpython the text is buffered and
+    an immediate repaint is triggered; otherwise it is a plain stdout write.
+    """
+    sink = None
+    try:
+        sink = _bpython_sink()
+    except Exception:
+        sink = None
+
+    if sink is not None:
+        on_write, wake = sink
+        try:
+            on_write(text)
+        except Exception:
+            pass  # fall through to a plain write below
+        else:
+            try:
+                wake()
+            except Exception:
+                pass
+            return
+
+    try:
+        sys.stdout.write(text)
+        sys.stdout.flush()
+    except Exception:
+        pass

tests/test_sim_trace_fmt.py

@@ -232,10 +232,10 @@ class TestTraceFormatterBasic:
         import re
         return re.sub(r'\033\[[0-9;]*m', '', s)
 
-    def test_starts_with_newline(self):
+    def test_ends_with_newline(self):
         fmt = TraceFormatter(mode="sim", decoder=decode_15693)
         result = fmt.format(0, bytes([0x26, 0x01, 0x00]))
-        assert result.startswith("\n")
+        assert result.endswith("\n")
 
     def test_sim_mode_tag(self):
         fmt = TraceFormatter(mode="sim", decoder=decode_15693)