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

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?

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.

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I think if there's any colour escapes, we bail and print it as-is without extra colour from us.

I agree with this.

But thinking further, our current highlighting logic relies on tokenize, yet pprint output has never made any guarantee that it must be valid Python source. __repr__ can return anything — it doesn't have to be tokenizer-friendly.

So, instead of special-casing \x1b[, how about

Probe the text with tokenize first,
-- if it can process the whole thing, highlight it;
-- if it chokes halfway through for any reason (ANSI escapes, illegal control chars, etc.), just print the raw text with no added colors.

No blacklist needed, no half-highlighted output.

What do you think?

 def _colorize_output(text):
     """Apply syntax highlighting."""
-    if "\x1b[" in text:
-        # If the text already contains ANSI escape sequences
-        # (for example, from a custom __repr__),
-        # return as-is to avoid breaking their color.
+    # Probe: if the text cannot be fully tokenized, fall back to plain text
+    # to avoid the "half-highlighted" problem.
+    try:
+        list(tokenize.generate_tokens(_StringIO(text).readline))
+    except (SyntaxError, tokenize.TokenError):
         return text
     colors = list(gen_colors(text))
     chars, _ = disp_str(text, colors=colors, force_color=True, escape=False)