Feature or enhancement

Proposal:

pprint.pformat() decides whether a container fits on the current line by building its complete one-line repr, and when it doesn't, it repeats that for each child. For deeply nested data the innermost items are therefore formatted once per enclosing level, so the time grows with size times depth.

import json, pprint, time
flat = json.loads("[" + ",".join(["1"] * 20000) + "]")
deep = json.loads("[" * 300 + ",".join(["1"] * 20000) + "]" * 300)
for o in flat, deep:
    t = time.perf_counter(); pprint.pformat(o); print(time.perf_counter() - t)

The nested version takes about 40x longer than the flat one (0.07 s vs 2.6 s on a release build). The fit check can stop once the line is full, which makes it cost at most the line width per level; output stays the same.

Has this already been discussed elsewhere?

This is a minor feature, which does not need previous discussion elsewhere

Links to previous discussion of this feature:

No response

Linked PRs

• gh-161114: Speed up pprint on deeply nested containers #161115