Traceback, Breadcrumbs, The code-context for a traceback could be neater in some specific cases

[leogott]

Call me Gretel, 'cause I'd like some Breadcrumbs with my traceback
Having usable, well-formatted tracebacks is important for everything unit testing.
rich.traceback does make tracebacks nicer to look at, but in some cases, I can imagine concrete improvements. However I'm not certain these can be boiled down to programmable rules. Thus a discussion and not an Issue.

Consider the following:

$ cat temp.py 
from enum import Enum

class A(Enum):
    a = 1

A.a = 2

$ python temp.py 
Traceback (most recent call last):
  File "/home/leogott/temp.py", line 6, in <module>
    A.a = 2
    ^^^
  File "/home/leogott/miniforge3/lib/python3.12/enum.py", line 860, in __setattr__
    raise AttributeError('cannot reassign member %r' % (name, ))
AttributeError: cannot reassign member 'a'

$ python temp.py   # with rich.traceback installed
╭────────────────────── Traceback (most recent call last) ──────────────────────╮
│ /home/leogott/temp.py:6 in <module>                                           │
│                                                                               │
│   3 class A(Enum):                                                            │
│   4 │   a = 1                                                                 │
│   5                                                                           │
│ ❱ 6 A.a = 2                                                                   │
│   7                                                                           │
│   8                                                                           │
│   9                                                                           │
│                                                                               │
│ ╭─────── locals ───────╮                                                      │
│ │    A = <enum 'A'>    │                                                      │
│ │ Enum = <enum 'Enum'> │                                                      │
│ ╰──────────────────────╯                                                      │
│                                                                               │
│ /home/leogott/miniforge3/lib/python3.12/enum.py:860 in __setattr__            │
│                                                                               │
│    857 │   │   """                                                            │
│    858 │   │   member_map = cls.__dict__.get('_member_map_', {})              │
│    859 │   │   if name in member_map:                                         │
│ ❱  860 │   │   │   raise AttributeError('cannot reassign member %r' % (name,  │
│    861 │   │   super().__setattr__(name, value)                               │
│    862 │                                                                      │
│    863 │   def _create_(cls, class_name, names, *, module=None, qualname=None │
│                                                                               │
│ ╭─────────── locals ───────────╮                                              │
│ │        cls = <enum 'A'>      │                                              │
│ │ member_map = {'a': <A.a: 1>} │                                              │
│ │       name = 'a'             │                                              │
│ │      value = 2               │                                              │
│ ╰──────────────────────────────╯                                              │
╰───────────────────────────────────────────────────────────────────────────────╯
AttributeError: cannot reassign member 'a'

some nitpicks:

• temp.py:L7-9 are just trailing newlines and could be omitted
• the called function ends at enum.py:L861, so all lines past that could be omitted; and enum.py:L857 is also not all that useful.
• Enum is only a local in the broadest sense. It's an imported and unmodified symbol
• knowing which environment was used can be extremely useful for solving very specific arcane errors caused by src being on the %path, and the way the path gets styled in a low-contrast color (but is still a usable link for certain IDEs) is pretty neat, but I still find it distracting.

an aside:

• enum.py:L860 is just a simple

Raise(exc=Call(func=Name(...), args=[BinOp(left=Constant(value='message %r'), op=Mod(), right=Name(...))], keywords=[]))

which feels like it could/should be special-cased?

actual shortcomings:

• the standard python traceback formatter now marks the "precise instruction" that caused the exception, which I think is pretty neat, and extremely useful in lines with nested function calls. Rich currently doesn't use this this(?) Or it does only on syntax errors? I didn't test this exhaustively
• the included context for setattr doesn't actually show me in which class this method is defined. something like breadcrumbs, a qualname or whatever would be nice.

Examples for how those could look like

│ ~/miniforge3/lib/python3.12/enum.py:860 in __setattr__                        │
│                                                                               │
│    479 class EnumType(type):                                                  │
│... 828 ︙   def __setattr__(cls, name, value):                                 │
│... 858 │   │   member_map = cls.__dict__.get('_member_map_', {})              │
│    859 │   │   if name in member_map:                                         │
│ ❱  860 │   │   │   raise AttributeError('cannot reassign member %r' % (name,  │
│    861 │   │   super().__setattr__(name, value)                               │
│                                                                               │

│ ~/miniforge3/lib/python3.12/enum.py:860                                       │
│     in EnumType.__setattr__                                                   │
│    858 │   │   member_map = cls.__dict__.get('_member_map_', {})              │
│    859 │   │   if name in member_map:                                         │
│ ❱  860 │   │   │   raise AttributeError('cannot reassign member %r' % (name,  │
│                                                                               │

│     in EnumType.__setattr__ @ ~/miniforge3/lib/python3.12/enum.py:860         │
│    858 │   │   member_map = cls.__dict__.get('_member_map_', {})              │
│    859 │   │   if name in member_map:                                         │
│ ❱  860 │   │   │   raise ...
AttributeError: cannot reassign member 'a' │
│                                                                               │

Thoughts?