xml.dom.pulldom.DOMEventStream leaks file handles opened by parse()

pulldom.parse() opens a file when called with a filename string, but the resulting DOMEventStream never closes it. The class has no close() method, no context manager support, and clear() just sets self.stream = None without closing.

This produces ResourceWarning: unclosed file and can lead to file descriptor exhaustion in long-running processes.

The documentation example at https://docs.python.org/3/library/xml.dom.pulldom.html#module-xml.dom.pulldom shows:

doc = pulldom.parse('sales_items.xml')
for event, node in doc:
    ...

— with no cleanup, so users following the docs will hit this.

Reproduction

import warnings, tempfile, os, gc
from xml.dom import pulldom

warnings.simplefilter('always', ResourceWarning)

fd, path = tempfile.mkstemp(suffix='.xml')
os.write(fd, b'<root><item>test</item></root>')
os.close(fd)

events = pulldom.parse(path)
for event, node in events:
    pass

# stream is still open after full iteration
print(f'stream.closed: {events.stream.closed}')  # False

# clear() doesn't close it either
events.clear()

del events
gc.collect()  # ResourceWarning: unclosed file ...

os.unlink(path)

The existing test in test_pulldom.py already works around this with self.addCleanup(handler.stream.close) (line 36), which further confirms the leak.

Suggested fix

Track whether parse() opened the file (vs. receiving a user-provided stream), then add close(), __enter__/__exit__, and __del__ with ResourceWarning to DOMEventStream. Update clear() to close owned streams.

This follows the same approach used for ElementTree.iterparse() (gh-140601).

Linked PRs

• gh-148437

Bắt đầu với DOMEventStream và pulldom.parse(), sau đó kiểm tra test_pulldom.py, đặc biệt là phần dọn dẹp hiện có quanh dòng 36. Tái hiện ResourceWarning và xác minh hành vi ownership đối với filename và các stream do người dùng cung cấp. Được xem là hoàn tất khi các bài kiểm thử bao quát việc dọn dẹp vòng đời và hành vi của context manager mà không làm rò rỉ các handle.