deduplicate keys in dict.fromkeys inference#3132
Open
nabhan06 wants to merge 1 commit into
Open
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Type of Changes
Description
infer_dict_fromkeyskeeps one entry per element without deduplicating, sodict.fromkeys("aab")infers a dict with keys"a", "a", "b"while the runtime call returns{"a": None, "b": None}; the same happens for list/tuple/dict inputs. Because each character becomes its ownConstnode, this also meansdict.fromkeys("x" * 10 ** 8)(a compact string the multiplication guard deliberately allows) expands into ~10^8 dict nodes while analyzing untrusted code, for what is really a single-key dict. The fix deduplicates the keys by value in each branch, matchingdict.fromkeyssemantics, which drops the inferred dict back to its real keys and removes the per-character node blowup.