Empty OPENAI_BASE_URL prevents fallback to default API endpoint

[thelyad]

Confirm this is an issue with the Python library and not an underlying OpenAI API

• This is an issue with the Python library

Describe the bug

I noticed a small issue in the base_url initialization logic: (

openai-python/src/openai/_client.py

Lines 163 to 166 in 656e3ca

	if base_url is None:
	base_url = os.environ.get("OPENAI_BASE_URL")
	if base_url is None:
	base_url = f"https://api.openai.com/v1"

)

if base_url is None:
    base_url = os.environ.get("OPENAI_BASE_URL")
if base_url is None:
    base_url = f"https://api.openai.com/v1"

If the environment variable OPENAI_BASE_URL is defined but empty (e.g., OPENAI_BASE_URL=""), then os.environ.get("OPENAI_BASE_URL") returns an empty string. As a result:

• base_url becomes ""
• the second condition (if base_url is None) is never triggered
• the intended fallback "https://api.openai.com/v1" is skipped

An empty string is not a valid base URL, so this can lead to confusing behavior.

To Reproduce

1. export OPENAI_BASE_URL=""
2. run the following:

from openai import OpenAI

client = OpenAI()
client.models.list()

3. Trigger an "openai.APIConnectionError: Connection error" error

Code snippets

OS

macOS

Python version

Python 3.12.2

Library version

2.15.0

[xXMrNidaXx]

Good catch on the empty string edge case. The current logic:

if base_url is None:
    base_url = os.environ.get('OPENAI_BASE_URL')
if base_url is None:
    base_url = f'https://api.openai.com/v1'

...uses is None for both checks, but os.environ.get() returns an empty string '' (not None) when the variable is set but empty. Empty string is falsy but not None, so the fallback never triggers.

The fix should be:

if base_url is None:
    base_url = os.environ.get('OPENAI_BASE_URL') or None  # converts '' to None
if base_url is None:
    base_url = 'https://api.openai.com/v1'

Or equivalently:

base_url = base_url or os.environ.get('OPENAI_BASE_URL') or 'https://api.openai.com/v1'

Workaround: Unset the environment variable entirely (unset OPENAI_BASE_URL or del os.environ['OPENAI_BASE_URL']) rather than setting it to an empty string. The bug only triggers when OPENAI_BASE_URL is defined but empty — if it's not set at all, os.environ.get() returns None and the fallback works correctly.

[giulio-leone]

This is addressed by #2939 — when OPENAI_BASE_URL is set to an empty string, it now falls back to the default API endpoint instead of constructing an invalid URL.

[mvanhorn]

I've submitted a fix for this in PR #2952. Uses or None to normalize empty env var strings, applied to both sync and async constructors.