Problem

Cannot catch a StopIteration raised from within a iterator.

Example

from typing import (
    Generator,
    Iterable,
    List
)
import sys
import pathlib
from itertools import islice

import numpy as np


def take(n: int, iterable: Iterable) -> List:
    taken = list(islice(iterable, 0, n))
    if len(taken) > 0:
        return taken
    else:
        print("Raising StopIteration")
        raise StopIteration("Nothing to take")     # <----- Raise StopIteration


def file_line_stream(path: str) -> Generator[str, None, None]:
    if not pathlib.Path(path).is_file():
        raise FileNotFoundError(f"file {path} does not exist or non file")
    try:
        _file = pathlib.Path(path)
        with _file.open() as f:
            for line in f:
                yield line.rstrip()
    except (IOError, FileNotFoundError) as e:
        raise RuntimeError("Read file failure") from e


def get_sentences(path_to_file, num_sentences):
    counter = 0
    stream = file_line_stream(path_to_file)
    try:
        while True:
            _lines = take(num_sentences, stream)
            print(f"Count {counter}:  yielding [{_lines[0]}]\n")
            yield np.array(_lines)
            counter += 1
    finally:
        stream.close()


def test():
    path_to_input = "test_has_two_lines.txt"
    generator = get_sentences(path_to_file=path_to_input, num_sentences=100)
    for i in range(10):
        # ----------------------------------------------------------------------
        # Want to catch the StopIteration raised from within the generator.
        # ----------------------------------------------------------------------
        try:
            next(generator)
        except StopIteration as e:
            print("Caught at StopIteration except")
            generator.close()

        except Exception as e:      # <--- Raised StopIteration will get caught here
            print("Caught at catch-all except: %s", sys.exc_info()[0])
            generator.close()
            raise e


if __name__ == '__main__':
    test()

Result

Count 0:  yielding [previous monthly <unk> of the major market index futures and standard & poor 's <unk> index options have produced spectacular volatility]

Raising StopIteration
Caught at catch-all except: %s <class 'RuntimeError'>
Traceback (most recent call last):
  File "test_050_word2vec.py", line 39, in get_sentences
    _lines = take(num_sentences, stream)
  File "test_050_word2vec.py", line 19, in take
    raise StopIteration("Nothing to take")     # <----- Raise StopIteration
StopIteration: Nothing to take

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "test_050_word2vec.py", line 67, in <module>
    test()
  File "test_050_word2vec.py", line 63, in test
    raise e
  File "test_050_word2vec.py", line 55, in test
    next(generator)
RuntimeError: generator raised StopIteration    <----- Converted into RuntimeError