Type-hinting of filter regression

[dycw]

Hi all,

I have noticed a regression in the type-hinting of filter. More precisely, on 6.125.0:

from hypothesis.strategies import booleans

reveal_type(booleans().filter(lambda n: n))     ■ Undefined name `reveal_type`     ■ Type of "booleans().filter(lambda n: n)" is "SearchStrategy[bool]"

But on 6.125.1:

from hypothesis.strategies import booleans

reveal_type(booleans().filter(lambda n: n))     ■ Undefined name `reveal_type`     ■■■ Return type of lambda is unknown

I suppose it must be in hypothesis-python-6.125.0...hypothesis-python-6.125.1 ?

[tybug]

hmm, both pyright and mypy report this as SearchStrategy[bool] for me:

from hypothesis import strategies as st

reveal_type(st.booleans().filter(lambda n: n))

/Users/tybug/Desktop/sandbox.py:3: note: Revealed type is "hypothesis.strategies._internal.strategies.SearchStrategy[builtins.bool]" # mypy
/Users/tybug/Desktop/sandbox.py:3:13 - information: Type of "st.booleans().filter(lambda n: n)" is "SearchStrategy[bool]" # pyright

mypy 1.15.0 (compiled: yes), pyright pyright 1.1.393. Are you using another type checker?

[dycw]

Hi @tybug ; I'm using pyright and this is probably due to strictness.

setup

~/work/hypothesis via 🐍 v3.11.10 (python-3.11)
❯ which python
/Users/derekwan/work/hypothesis/.direnv/python-3.11/bin/python

~/work/hypothesis via 🐍 v3.11.10 (python-3.11)
❯ uv pip install hypothesis
Using Python 3.11.10 environment at: .direnv/python-3.11
Resolved 3 packages in 62ms
Installed 3 packages in 7ms
 + attrs==25.1.0
 + hypothesis==6.125.3
 + sortedcontainers==2.4.0

~/work/hypothesis via 🐍 v3.11.10 (python-3.11)
❯ which pyright
/opt/homebrew/bin/pyright

~/work/hypothesis via 🐍 v3.11.10 (python-3.11)
❯ pyright --version
pyright 1.1.393

~/work/hypothesis via 🐍 v3.11.10 (python-3.11)
❯ cat foo.py
───────┬─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: foo.py
───────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ from hypothesis.strategies import booleans
   2   │
   3   │ reveal_type(booleans().filter(lambda n: n))
───────┴─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

In normal mode:

~/work/hypothesis via 🐍 v3.11.10 (python-3.11)
❯ cat pyproject.toml
───────┬─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: pyproject.toml
───────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ [tool.pyright]
   2   │ typeCheckingMode = "normal"
───────┴─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

~/work/hypothesis via 🐍 v3.11.10 (python-3.11)
❯ pyright .
Config "typeCheckingMode" entry must contain "off", "basic", "standard", or "strict".
/Users/derekwan/work/hypothesis/foo.py
  /Users/derekwan/work/hypothesis/foo.py:3:13 - information: Type of "booleans().filter(lambda n: n)" is "SearchStrategy[bool]"
0 errors, 0 warnings, 1 information

Now in strict mode:

~/work/hypothesis via 🐍 v3.11.10 (python-3.11)
❯ cat pyproject.toml
───────┬─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       │ File: pyproject.toml
───────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
   1   │ [tool.pyright]
   2   │ typeCheckingMode = "strict"
───────┴─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────

~/work/hypothesis via 🐍 v3.11.10 (python-3.11)
❯ pyright .
/Users/derekwan/work/hypothesis/foo.py
  /Users/derekwan/work/hypothesis/foo.py:3:13 - error: Type of "filter" is partially unknown
    Type of "filter" is "(condition: (Unknown) -> object) -> SearchStrategy[bool]" (reportUnknownMemberType)
  /Users/derekwan/work/hypothesis/foo.py:3:13 - information: Type of "booleans().filter(lambda n: n)" is "SearchStrategy[bool]"
  /Users/derekwan/work/hypothesis/foo.py:3:38 - error: Type of parameter "n" is unknown (reportUnknownLambdaType)
  /Users/derekwan/work/hypothesis/foo.py:3:41 - error: Return type of lambda is unknown (reportUnknownLambdaType)
3 errors, 0 warnings, 1 information

[tybug]

Thanks. I still can't reproduce:

 ~/Desktop/temp λ pyright --verbose '/Users/tybug/Desktop/temp/main.py'
Loading pyproject.toml file at /Users/tybug/Desktop/temp/pyproject.toml
Auto-excluding **/node_modules
Auto-excluding **/__pycache__
Auto-excluding **/.*
Assuming Python version 3.13.1.final.0
Execution environment: python
  Extra paths:
    (none)
  Python version: 3.13.1.final.0
  Python platform: Darwin
  Search paths:
    /opt/homebrew/lib/python3.11/site-packages/pyright/dist/dist/typeshed-fallback/stdlib
    /Users/tybug/Desktop/temp
    /Users/tybug/Desktop/temp/typings
    /opt/homebrew/lib/python3.11/site-packages/pyright/dist/dist/typeshed-fallback/stubs/...
    /opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13
    /opt/homebrew/Cellar/python@3.13/3.13.1/Frameworks/Python.framework/Versions/3.13/lib/python3.13/lib-dynload
    /opt/homebrew/lib/python3.13/site-packages
    /opt/homebrew/Cellar/openvino/2024.6.0_1/libexec/lib/python3.13/site-packages
Found 1 source file
pyright 1.1.394
/Users/tybug/Desktop/temp/main.py
  /Users/tybug/Desktop/temp/main.py:3:13 - information: Type of "booleans().filter(lambda n: n)" is "SearchStrategy[bool]"
0 errors, 0 warnings, 1 information 
Completed in 0.31sec
 ~/Desktop/temp λ cat pyproject.toml 
[tool.pyright]
typeCheckingMode = "strict"
 ~/Desktop/temp λ cat main.py 
from hypothesis.strategies import booleans

reveal_type(booleans().filter(lambda n: n))
 ~/Desktop/temp λ python3
Python 3.12.3 (main, Apr  9 2024, 08:09:14) [Clang 15.0.0 (clang-1500.1.0.2.5)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import hypothesis
>>> hypothesis.__version__
'6.125.3'
>>> ^D
 ~/Desktop/temp λ 

I also tried pythonVersion = "3.11" in pyproject.toml to match your environment, but that didn't reproduce either.