In the --ignore-dir handling of trace.py, the following is done:

                s = s.replace("$prefix",
                              os.path.join(sys.base_prefix, "lib",
                                           "python" + sys.version[:3]))
                s = s.replace("$exec_prefix",
                              os.path.join(sys.base_exec_prefix, "lib",
                                           "python" + sys.version[:3]))

This does not do what is expected on 64-bit Fedora and newer Debian since the proper directory is /usr/lib64/python2.7 or /usr/lib/$triple/python2.7. Just the libsuffix can't be changed either since Fedora also has /usr/lib/python2.7 for arch-independent modules. It'd be nice if $prefix were replaced with the following directories from sysconfig.get_paths(): platstdlib, platlib, purelib, and stdlib.

It also erroneously replaces things like '$prefixpath'. It should probably do split the path on the path separators and only replace components that are equal to $prefix or $exec_prefix (so that the '$' can be escaped for directories named as such literally, but that would require a pass to parse the escapes).

New changeset 4fac7ed43ebf1771a8fe86fdfe7b9991f3be78cd by Victor Stinner in branch 'master':
bpo-21016: pydoc and trace use sysconfig (GH-18476)
https://github.com/python/cpython/commit/4fac7ed43ebf1771a8fe86fdfe7b9991f3be78cd

New changeset ca133e53fafdec1aa77613fcb7558deed959383f by Miss Islington (bot) in branch '3.7':
bpo-21016: pydoc and trace use sysconfig (GH-18476)
https://github.com/python/cpython/commit/ca133e53fafdec1aa77613fcb7558deed959383f

New changeset ac6f4d2db703c0ff88e496bcb7b7fe55cf2ac458 by Miss Islington (bot) in branch '3.8':
bpo-21016: pydoc and trace use sysconfig (GH-18476)
https://github.com/python/cpython/commit/ac6f4d2db703c0ff88e496bcb7b7fe55cf2ac458

Thanks Ben Boeckel for the bugfix. Sorry for the delay (6 years)! But it's now fixed in 3.7, 3.8 and master branches.

Thanks!

Should I file a new issue for the other (less urgent) problem mentioned at the bottom or is it not really worth fixing?

> It also erroneously replaces things like '$prefixpath'. It should probably do split the path on the path separators and only replace components that are equal to $prefix or $exec_prefix (so that the '$' can be escaped for directories named as such literally, but that would require a pass to parse the escapes).

> It also erroneously replaces things like '$prefixpath'. It should probably do split the path on the path separators and only replace components that are equal to $prefix or $exec_prefix (so that the '$' can be escaped for directories named as such literally, but that would require a pass to parse the escapes).

re.sub() can be used to leave $prefixpath unchanged. Yeah, please open a separed issue. Sorry, I missed this part of the bug report.