Closed
Description
Bug Report
The Prime number sieve with generators Mypy with static typing example does not pass on mypy.
It's also not clear what needs to be done to make the example work. Typing numbers seems to work.
To Reproduce
# Taken directly from https://mypy-lang.org/examples.html
import itertools
from typing import Iterator
def iter_primes() -> Iterator[int]:
# An iterator of all numbers between 2 and
# +infinity
numbers = itertools.count(2)
# Generate primes forever
while True:
# Get the first number from the iterator
# (always a prime)
prime = next(numbers)
yield prime
# This code iteratively builds up a chain
# of filters...
numbers = filter(prime.__rmod__, numbers)
for p in iter_primes():
if p > 1000:
break
print(p)https://mypy-play.net/?mypy=master&python=3.9&gist=52970ddb2c5cd827dafa8f8af5219f89
Expected Behavior
No errors.
Actual Behavior
main.py:18: error: Incompatible types in assignment (expression has type "filter[int]", variable has type "count[int]") [assignment]
Found 1 error in 1 file (checked 1 source file)
Your Environment
- Mypy version used: mypy master, mypy 1.10.0 (I tried all the versions on the playground on https://mypy-play.net/, but none seem to work. I think it worked with 0.750 but I haven't tested it to be sure.)
- Mypy command-line flags: None
- Mypy configuration options from
mypy.ini(and other config files): None - Python version used: 3.12, 3.9
Suggested fix
I guess changing numbers = itertools.count(2) to numbers: Iterator[int] = itertools.count(2) seems to work. Perhaps we should update the mypy example?