Custom __str__ vs __repr__

[ajwood]

I'm trying to add some pretty colors to the console representation of a custom object. The Console Prorotol docs describe how to do exactly that, by defining a __rich__ method. This method seems to override the built-in __str__ (although I find the docs actually suggest it would be __repr__). This is great, so when I rich.print(MyObj(123)), its __rich__ method kicks in and everything is beautiful. However with rich.print([MyObj(123), MyObj(456)]), it doesn't use the custom rendering.

I found the Rich Repr Protocol, but that seems to solve a different problem.

Is it possible to do what I'm attempting, implement custom methods to replace both __str__ and __repr__ for the purposes of custom rich.print output?

[willmcgugan]

What would you expect printing a list of MyObj to do?

When you print a container like a list, you are invoke pretty printing, which is designed for displaying data structures.

[ajwood]

What would you expect printing a list of MyObj to do?

Not sure exactly, but what rich does by default seems to make sense. IIUC, it applies some built-in logic to parse the __repr_ string, and does its best to make it pretty.

The part that was surprising me is that the __rich__ hook exists to define custom formatting for when python goes for its __str__ representation, but there doesn't seem to be an equivalent for __repr__ (I thought __rich_repr__ would be the answer, but that doesn't appear to support custom coloring). So I was expecting to find a way to have full control of how the custom object gets printed, regardless of whether python wants to render it with __str__ or __repr__.

To quickly describe my current scenario, I have a filesystem tree that follows a structured layout. For an entry in this tree e.g. aaa/bbb/ccc/ddd:1.2.3:4567, trying to make it easy to look at, where each item in the colon-separated component comes out a different colour, even in the case where I'm printing a list of these path items.

[ajwood]

IIUC, it applies some built-in logic to parse the _repr string, and does its best to make it pretty.

Oh I see where I went wrong there, the built-in parsing is on list's __str__ output, which happened to have called MyObj's __repr__. But by the time rich.print comes into the picture, it's too late?

[ajwood]

FWIW here's a working example of what I'm trying:

import itertools

from rich import print


class Foo:
    def __init__(self, tag: str):
        """A toy class with a colon-separated tag"""
        self.tag = tag

    def __rich__(self) -> str:
        # alternate tag component colours
        colors = itertools.cycle(("red", "green"))
        x = "[blue]:[blue/]".join(
            "[{color}]{t}[{color}/]".format(t=t, color=next(colors))
            for t in self.tag.split(":")
        )
        return x

    def __rich_repr__(self) -> str:
        yield self.tag


f = Foo("aaa:bbb:1.2.3:4567")
print(f)  # renders with alternating colours
print([f, f])  # can't get `f` rendered with custom format logic

[willmcgugan]

I see. No, I'm afraid you're asking too much from Rich there. When you are printing a dictionary you are essentially asking for a repr of it and its contents. It won't do any of the fancy formatting that you can do via __rich__.

By the looks of it, what you want is highlighting. If you are familiar with regexes, you can create a highlighter to automatically colorize certain patterns.

[ajwood]

Ohh indeed that highlighting looks very promising, I'll check it out. Thanks for taking the time to help!