Compatibility with 3.15 lazy imports

[sentrivana]

Hey folks. I was just testing the Sentry SDK on a Python 3.15 beta (3.15.0b3) -- we use httpcore in our experimental HTTP2 transport -- and ran into a possible problem when httpcore is used with lazy imports.

The problem, distilled, can be triggered as follows:

• set up a uv environment that uses Python 3.15
• install latest httpcore in it
• save this as repro.py:

import httpcore
print(httpcore.ConnectionPool)

• run the above with PYTHON_LAZY_IMPORTS=all uv run repro.py

You'll get this stacktrace:

Traceback (most recent call last):
  File "<redacted>/repro.py", line 1, in <module>
    import httpcore
ImportError: lazy import of 'httpcore' raised an exception during resolution

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

Traceback (most recent call last):
  File "<redacted>/repro.py", line 2, in <module>
    print(httpcore.ConnectionPool)
          ^^^^^^^^
  File "<redacted>/.venv/lib/python3.15/site-packages/httpcore/__init__.py", line 141, in <module>
    setattr(__locals[__name], "__module__", "httpcore")  # noqa
    ~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
AttributeError: 'lazy_import' object has no attribute '__module__' and no __dict__ for setting new attributes. Did you mean '.__reduce__' instead of '.__module__'?

Thought I'd raise this with y'all as a heads up if you think this is actionable and httpcore should work with PYTHON_LAZY_IMPORTS=all (which is not a given).

[meyshad]

This is a compatibility bug in httpcore's public-name cleanup, not in ConnectionPool itself. At the end of httpcore/__init__.py, httpcore loops through __all__ and writes __module__ on every imported object. With Python 3.15's global lazy-import mode, those entries can still be types.LazyImportType proxies, and the proxy does not allow that assignment.

A caller-side workaround is to import httpcore eagerly, then restore lazy mode:

import sys

sys.set_lazy_imports("normal")
import httpcore
sys.set_lazy_imports("all")

print(httpcore.ConnectionPool)

A small cross-version library fix would skip the cosmetic __module__ rewrite for unresolved proxies:

import types

lazy_import_type = getattr(types, "LazyImportType", None)
__locals = locals()

for __name in __all__:
    if __name.startswith(("__", "SOCKET_OPTION")):
        continue

    value = __locals[__name]
    if lazy_import_type is not None and isinstance(value, lazy_import_type):
        continue

    setattr(value, "__module__", "httpcore")

The failing loop is visible in httpcore/init.py. Skipping the rewrite only leaves the original implementation module in introspection output; it does not change the exported object. Python 3.15 documents types.LazyImportType specifically for detecting these proxies.