IronLanguages / IronLanguages/ironpython3
Creating a set from a dict rehashes the keys
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CPython compatibility
- Dominant language
- C#
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Description
class HashCountingInt(int):
def __init__(self, *args):
self.hash_count = 0
def __hash__(self):
self.hash_count += 1
return int.__hash__(self)
n = 10
d = dict.fromkeys(map(HashCountingInt, range(n)))
assert sum(elem.hash_count for elem in d) == n
s = set(d) # this should not re-compute the hashes
assert sum(elem.hash_count for elem in d) == n
This issue comes from test_set.test_do_not_rehash_dict_keys.
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by running or reading the test_set.test_do_not_rehash_dict_keys test and reproduce the dict-to-set behavior shown in the issue. Trace the set construction path responsible for the extra hash calls, then make the test pass while preserving the existing hash count.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- csharp, python
- Domain
- backend
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 45/100