[New-bugs-announce] [issue46742] Add '-d $fd' option to trace module, akin to bash -x feature

Charles Howes report at bugs.python.org
Sun Feb 13 16:39:31 EST 2022

New submission from Charles Howes <github.com at ch.pkts.ca>:

The 'trace' module logs trace output to stdout, intermingled with regular program output.  This is a problem when you want to read either the trace output or the normal output of the program separately.

To separate the trace output, it could be written to a file or to another file descriptor.

A pull request has been created that fixes this by mimicking bash's behaviour: bash can be told to write trace output to a different file descriptor using the BASH_XTRACEFD shell variable: `exec 42> xtrace.out; BASH_XTRACEFD=42; ...`

Usage of this new feature:

  python -m trace -t -d 111 your_program.py 111> /tmp/your_trace.txt


  t = Trace(count=1, trace=1, trace_fd=1, countfuncs=0, countcallers=0, ignoremods=(), ignoredirs=(), infile=None, outfile=None, timing=False)

* `bash -x` sends trace logs to stderr by default; `python -m trace -t` sends them to stdout.  I wanted to change Python to match, but was worried that this might break existing code.  

* Also considered writing trace logs to the file specified with the `-f FILE` option, but worried that it would mess up the count file if `-t` and `-c` were used together.

components: Library (Lib)
messages: 413197
nosy: PenelopeFudd
priority: normal
severity: normal
status: open
title: Add '-d $fd' option to trace module, akin to bash -x feature
type: enhancement
versions: Python 3.11

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