While working on bpo-24644, I noticed that the help for python -mtrace is quite wrong.

$ python -mtrace --help
Usage: /usr/lib/python3.4/trace.py [OPTIONS] <file> [ARGS]

Meta-options:
--help Display this help then exit.
--version Output version information then exit.

Otherwise, exactly one of the following three options must be given:
-t, --trace Print each line to sys.stdout before it is executed.
-c, --count Count the number of times each line is executed
and write the counts to .cover for each
module executed, in the module's directory.
See also --coverdir', --file', --no-report' below. -l, --listfuncs Keep track of which functions are executed at least once and write the results to sys.stdout after the program exits. -T, --trackcalls Keep track of caller/called pairs and write the results to sys.stdout after the program exits. -r, --report Generate a report from a counts file; do not execute any code. --file' must specify the results file to
read, which must have been created in a previous run
with `--count --file=FILE'.

<elided modifier flags>

1. Obviously, there are more than 3 options there.
2. Simple testing suggests that it is at least possible to pass both -t and -c simultaneously. I haven't tested other combinations.

Maybe it is time to rewrite trace module argument parser using argparse
and get an "always correct" auto-generated help for free?

Added a patch that clears up the incorrect help. It now accurately reflects the only constraints that the code actually puts on the arguments:

    if listfuncs and (count or trace):
        _err_exit("cannot specify both --listfuncs and (--trace or --count)")

    if not (count or trace or report or listfuncs or countcallers):
        _err_exit("must specify one of --trace, --count, --report, "
                  "--listfuncs, or --trackcalls")

To reflect both of those constraints, and only those constraints, the part of the help message in question now reads:

Otherwise, at least one of the following options must be given:
-t, --trace Print each line to sys.stdout before it is executed.
-c, --count Count the number of times each line is executed
and write the counts to .cover for each
module executed, in the module's directory.
See also --coverdir', --file', --no-report' below. -l, --listfuncs Keep track of which functions are executed at least once and write the results to sys.stdout after the program exits. Cannot be specified alongside --traceor--count. -T, --trackcalls Keep track of caller/called pairs and write the results to sys.stdout after the program exits. -r, --report Generate a report from a counts file; do not execute any code. --file' must specify the results file to
read, which must have been created in a previous run
with `--count --file=FILE'.

A re-write using argparse is submitted in the bpo-22642, that's why I'm closing this issue. Changes from Evan's patch were incorporated in the submitted patch there.