Hi!
Thanks everyone for the interest and for the suggested options! I would
like ro add my two coins and clarify some moments as the original requester
of this feature.
1. We need this lazy `__repr__` calculation inside our debugger, where we
work with different user's objects. Usually it isn't some specific type,
for which you know that it'll be big and its `__repr__` calculation will be
slow (like, for example, pandas.DataFrame). Sometimes it can be just a
composition of builtin types, like in the example below.
On the top level it's just a `dict` with 10 elements and you don't expect
its `repr()` to be slow, but it takes 13 secs on my machine to calculate
it.
```
import time
def build_data_object():
data = dict()
for i in range(10):
temp_dict = dict()
for j in range(10):
temp_dict[str(j)] = "a" * 30000000
data[str(i)] = temp_dict
return data
obj = build_data_object()
start = time.time()
repr(obj)
finish = time.time()
print("Time: %.2f" % (finish - start))
```
2. I also agree it isn't the best idea to add additional parameters to
`repr` or `str`. Just a function like `lazy_repr` implemented in stdlib
will be already very useful.
3. But I also believe this issue can't be solved without changes in the
language or stdlib, because you can't predict the length of `repr` for an
object of unknown type without calculation of the whole string. But I hope
it should be possible to check current buffer size during `__repr__`
generation and interrupt it when it reaches the limit. (sorry, I'm not a
CPython developer and I might be too naive here, so correct me if I'm
wrong).
Elizaveta Shashkova.
сб, 25 июл. 2020 г. в 13:27, Serhiy Storchaka <storch...@gmail.com>:
> 24.07.20 18:10, Gábor Bernát пише:
> > I would like to have a lazy repr evaluation for the objects! Sometimes
> users have many really large objects, and when debugger is trying to show
> them in Variables View (=show their string representation) it can takes a
> lot of time. We do some tricks, but they not always work. It would be
> really-really cool to have parameter in repr, which defines max number of
> symbols we want to evaluate during repr for this object.
> > Maybe repr is not the best here, because that should be interpreter
> meaningful, but instead the __str__ method that's better for this. Maybe we
> could pass in an optional limit argument to these methods, so that the user
> can decide what to print depending on how many characters he has left?
> >
> > Any takes, better ideas how we could help this problem?
>
> We need a structural repr protocol, which would represent complex object
> as a structure containing items and attributes, so pprint() would know
> how to format a multiline text representation, and graphic tools could
> represent objects as a tree, with collapsed by default deep children and
> long sequences which can be expanded interactively. It was discussed in
> the past, but we still do not have good specification of such protocol.
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