repr () not used in window displays (Issue #1661 continued)

[mrolle45]

In safe_repr.py, ptvsd estimates whether repr (obj) might be too long to send to the IDE. In my code, I have a class derived from list, and if I have more than two levels of nesting, it is considered too long.

Please consider the following solution: If the obj being displayed has a method called 'safe_repr', then this is called directly. I put the following in my local copy of safe_repr.py:
def call(self, obj):

•    try: return obj.__safe_repr__ ()
  

•    except Exception: pass
  

The name 'safe_repr' is something I made up. You might want to provide some other way to tell SafeRepr (obj) that repr (obj) is OK to use.

Environment data

• VS Code version: 2017
• OS and version: Windows 10
• Python version: 3.7

[int19h]

This is something that really should be tackled on the Python side of things, because it's a problem that affects all IDEs (and really anything that has to visualize Python data structures). This is not a trivial design issue, because such a hook needs to allow objects to coordinate - e.g. in your case you don't want to apply nesting limitations, but other collections might.

OTOH if Python does it, it can be designed much more flexibly than our implementation - for example, instead of expecting the repr to return the value, it can supply a builder object with methods to append text, and to recursively invoke repr on a contained value; and the builder can then keep track of things like nesting level or number of elements rendered. The stdlib collections could then also implement it properly.

@brettcannon, is that something that would be PEP-worthy? The gist is to have a form of repr() that can limit the size of the output, for cases like collections of thousands of elements, or lists that nest so deeply that you get too many [...].

[brettcannon]

@int19h you could propose it on python-ideas and see if people are positive on the idea.