Workaround for copy/pasting Slack's broken multiline code blocks

print-slack-clipboard

#!/usr/bin/env python3
"""
Slack's new WYSIWYG format broke copy/pasting multiline code blocks:
blank lines are omitted when pasting as plain text.

If you can get the HTML contents of the clipboard, this script can
output the expected text, blank lines and all.

The macOS clipboard is complicated, and the built-in `pbpaste` command
won't let you get the contents as HTML. (The `-Prefer` option seems to
not do anything at all: there's even a related bug documented in the
`pbpaste` man page.) Christopher Brown's `macos-pasteboard` project
works well for me: https://github.com/chbrown/macos-pasteboard (Thanks,
Christopher!) (Linux probably has similar tools available.)

Suggested usage with `macos-pasteboard` and the built-in `pbcopy`:

    pbv public.html | print-slack-clipboard | pbcopy

"""
import sys
from html.parser import HTMLParser


class SlackClipboardPrinter(HTMLParser):

    def handle_starttag(self, tag, attrs):
        if tag == 'br':
            print()
        elif tag == 'span':
            for attr in attrs:
                if attr == ('data-stringify-type', 'paragraph-break'):
                    print('\n')

    def handle_data(self, data):
        print(data, end='')


SlackClipboardPrinter().feed(str(sys.stdin.read()))

NOTE: Looks like this won't convert charrefs (e.g., <) on Python < 3.5: change SlackClipboardPrinter() to SlackClipboardPrinter(convert_charrefs=True) in Python 3.4 (or upgrade your Python 😉)