tests/md5sum.py

pyoxidizer: update README.md with several small fixes

Currently, pyoxidizer.bzl does not mention the git commit that should be checked
out, so these instructions are a bit difficult to follow right now (impossible,
technically), so I removed the instruction to `git checkout <Git commit>` and
the admonition to use a specific version of PyOxidizer. I don't even know if the
project currently builds with the "0.7.0-pre" version that was previously
recommended.

As fallout from that change to not "pin" to a specific PyOxidizer, I had to
update the Python version to use when running the tests.

While here, I added a recommendation to use `--release`, as the primary reason
for this project is performance, and it may have been leaving some on the table
to not have that there.

Differential Revision: https://phab.mercurial-scm.org/D11698

#!/usr/bin/env python3
#
# Based on python's Tools/scripts/md5sum.py
#
# This software may be used and distributed according to the terms
# of the PYTHON SOFTWARE FOUNDATION LICENSE VERSION 2, which is
# GPL-compatible.

from __future__ import absolute_import

import hashlib
import os
import sys

try:
    import msvcrt

    msvcrt.setmode(sys.stdout.fileno(), os.O_BINARY)
    msvcrt.setmode(sys.stderr.fileno(), os.O_BINARY)
except ImportError:
    pass

for filename in sys.argv[1:]:
    try:
        fp = open(filename, 'rb')
    except IOError as msg:
        sys.stderr.write('%s: Can\'t open: %s\n' % (filename, msg))
        sys.exit(1)

    m = hashlib.md5()
    try:
        for data in iter(lambda: fp.read(8192), b''):
            m.update(data)
    except IOError as msg:
        sys.stderr.write('%s: I/O error: %s\n' % (filename, msg))
        sys.exit(1)
    sys.stdout.write('%s  %s\n' % (m.hexdigest(), filename))

sys.exit(0)