Python 3.15: Lazy imports break httpx.

[anonymousx97]

If you enable -X lazy_imports=all added in python 3.15 the setattr block in httpx/__init__.py breaks.

>>> import httpx

>>> httpx.AsyncClient()

Traceback (most recent call last):
  File "<python-input-9>", line 1, in <module>
    httpx.AsyncClient()
    ~~~~~~~~~~~~~~~~~^^
  File "/opt/venv/lib/python3.15/site-packages/httpx/_client.py", line 1402, in __init__
    self._transport = self._init_transport(
                      ~~~~~~~~~~~~~~~~~~~~^
        verify=verify,
        ^^^^^^^^^^^^^^
    ...<5 lines>...
        transport=transport,
        ^^^^^^^^^^^^^^^^^^^^
    )
    ^
  File "/opt/venv/lib/python3.15/site-packages/httpx/_client.py", line 1445, in _init_transport
    return AsyncHTTPTransport(
        verify=verify,
    ...<4 lines>...
        limits=limits,
    )
  File "/opt/venv/lib/python3.15/site-packages/httpx/_transports/default.py", line 294, in __init__
    import httpcore
  File "/opt/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__'?

[kasparovabi]

The failing code is in httpcore rather than httpx. httpx imports httpcore inside HTTPTransport.__init__ and AsyncHTTPTransport.__init__, and an import inside a function is never lazy, so httpcore's __init__.py really runs at that point. Its own module-level from ._api import ... lines are top-level imports, so -X lazy_imports=all makes them lazy. Until something reads those names as attributes they are lazy_import placeholders in the module namespace, and the loop at the end of the file reads them straight out of locals().

__locals = locals()
for __name in __all__:
    if not __name.startswith(("__", "SOCKET_OPTION")):
        setattr(__locals[__name], "__module__", "httpcore")

A plain dict lookup returns the placeholder, so setattr lands on the lazy_import object.

Reproduced on the python:3.15-slim image (3.15.0) with httpx 0.28.1 and httpcore 1.0.9.

$ python -X lazy_imports=all -c "import httpcore; httpcore.Request"
AttributeError: 'lazy_import' object has no attribute '__module__' and no __dict__ for setting new attributes. ...

import httpcore on its own succeeds under all, because that top-level import is itself lazy. The error appears on first use.

Until httpcore changes, a lazy imports filter that keeps httpcore's own imports eager works around it.

import sys

sys.set_lazy_imports_filter(lambda importer, name, fromlist=None: importer != "httpcore")

With that set before httpx is used, httpx.Client().get(...) and AsyncClient().get(...) against a local server both return 200 under -X lazy_imports=all.

In httpcore itself, reading the names as module attributes instead of from the locals() dict resolves the placeholders first.

import sys as __sys

__module = __sys.modules[__name__]
for __name in __all__:
    # Exclude SOCKET_OPTION, it causes AttributeError on Python 3.14
    if not __name.startswith(("__", "SOCKET_OPTION")):
        setattr(getattr(__module, __name), "__module__", "httpcore")  # noqa

With that change the same sync and async requests return 200 under -X lazy_imports=all, httpcore.Request.__module__ is still "httpcore", and the default mode on 3.15 and 3.13 behaves as before. I have not run httpcore's test suite against it.

[anonymousx97]

Thanks for a fast reply.
And yes I'm filtering out problematic lazy libs in project.
I hope they update for py3.15 support soon.

[kasparovabi]

The change is now on a branch with a regression test and a CHANGELOG line: kasparovabi/httpcore@7042264 (fix/lazy-imports-all). The test runs the import in a -X lazy_imports=all subprocess, is skipped before 3.15, and fails without the change. httpcore's suite passes on 3.13 and 3.15 with it.

Opening a pull request on encode/httpcore is currently limited to collaborators, so I am leaving it here in case a maintainer wants to pick it up.