What if duck types are unions of all the ducklings
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- Dominant language
- Python
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Description
If the duck typed types were actually unions of all the ducklings then it would fix a bunch of edge cases that arise.
And would make this feature more easily understood and discovered.
def func1(c: complex):
reveal_type(c) # float | int | complex
def func2(f: float):
reveal_type(f) # float | int
def func3(b: bytes):
reveal_type(b) # bytes | bytearray | memoryview
def func4(u: unicode): # python 2 moment
reveal_type(u) # unicode | str
edge cases:
def func(f: float):
f.is_integer() # error: int has no member "is_integer"
def func(f: float):
if not isinstance(f, float):
print("hi") # no 'unreachable code' error
reveal_type(f) # int | complex
It would also be useful to have type types for float and bytes, when you want exactly float and don't want any stinking ints.
Related #11511, #11145
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 with the examples in this issue and compare the proposed union semantics with related issues #11511 and #11145. Resolve how duck-typed types should behave, including exact float and bytes types and isinstance narrowing; done requires an agreed design and corresponding type-checker behavior.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- compilers
- Issue type
- Feature
- Difficulty
- 5/5
- Estimated time
- Over a week
- Activity status
- Stale
- Clarity
- Needs clarification
- Newbie friendliness
- 25/100