gh-145217: Add colour to pprint output

[hugovk]

Example:

import pprint

data = ["spam", "eggs", ("lumberjack", "knights"), "ni", 42, None]
data.insert(0, data)

pprint.pp(data)
pprint.pprint(data)
pprint.PrettyPrinter().pprint(data)

• Issue: Add colour to pprint output #145217

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📚 Documentation preview 📚: https://cpython-previews--145218.org.readthedocs.build/

[sunmy2019]

Shall we add a bool(color) conversion just as a few lines above?

        self._compact = bool(compact)
        self._expand = bool(expand)

[hugovk]

Sure, can do, but not sure if it's necessary?

[sunmy2019]

Do we have explicit test for color=True and can_colorize=False? It's an end to end test.

something like

        obj = {"key": "value"}
        stream = io.StringIO()

        # color=True should not produce no ANSI codes for streams
        # that do not support color
        pprint.pprint(obj, stream=stream, color=True)
        result = stream.getvalue()
        self.assertNotIn("\x1b[", result)

[sunmy2019]

If user's __repr__ contains color, it would break the color.

Code

import os
import pprint

os.environ["FORCE_COLOR"] = "1"
os.environ["NO_COLOR"] = ""


class Colorful:
    """something with a colorful repr"""

    def __repr__(self):
        return "\x1b[31mred\x1b[0m"

pprint.pprint({"a": Colorful(), "b": 42, "c": "hello"}, color=True)

What should we do for this case?

1. Document and keep as is?
2. Pre check escape sequence before colorize?
3. Other techniques for this?

[hugovk]

2. Pre check escape sequence before colorize?

I think if there's any colour escapes, we bail and print it as-is without extra colour from us. So we get something like this:

And I expect colour is rare in users' __repr__s? If so, this won't happen often, and when it does, we don't override any of their own colour or need more complex handling. And they don't end up with just a green "a" like in your example.