aio-libs/aiohttp · warning · LookupError

Proxying is disallowed for

Error message

Proxying is disallowed for `{url.host!r}`

What it means

get_env_proxy_for_url raises LookupError when the URL's host matches the proxy_bypass list (typically the NO_PROXY environment variable). This means proxying to that host is explicitly disallowed by the environment configuration, so aiohttp refuses to route the request through a proxy.

Solutions

1. Remove the host from the NO_PROXY environment variable if proxying is actually intended
2. Pass the proxy explicitly via the proxy= parameter to bypass env resolution: session.get(url, proxy='http://proxy:8080')
3. Adjust NO_PROXY patterns to be more specific so they do not match the intended target

Example fix

# before (NO_PROXY=localhost causes this)
proxy, proxy_auth = get_env_proxy_for_url(URL('http://localhost:8080/api'))

# after — pass proxy explicitly, bypassing env check
resp = await session.get('http://localhost:8080/api', proxy='http://corporate-proxy:3128')

import os
from urllib.request import proxy_bypass

def can_proxy(host):
    return not (host and proxy_bypass(host))

if not can_proxy(url.host):
    logger.info('Host %s is in NO_PROXY; using direct connection', url.host)

from aiohttp.helpers import get_env_proxy_for_url
try:
    proxy, proxy_auth = get_env_proxy_for_url(url)
except LookupError as e:
    if 'disallowed' in str(e).lower():
        proxy, proxy_auth = None, None  # direct connection
    raise

When it happens

Trigger: Calling get_env_proxy_for_url(url) when url.host is in the NO_PROXY/no_proxy list. The proxy_bypass function (from urllib.request) returns True for hosts matching NO_PROXY patterns like 'localhost', '127.0.0.1', '*.internal', etc.

Common situations: NO_PROXY includes 'localhost' but code tries to use an env proxy for a localhost URL; NO_PROXY wildcard patterns that unexpectedly match the target host; corporate environments with broad NO_PROXY ranges that catch internal service hosts.

Related errors

• No .netrc file found
• No proxies found for
• aiohttp only supports http(s) proxies
• No entry for found in the `.netrc` file.
• base_url must have a trailing '/'

AI-assisted analysis of aio-libs/aiohttp@d041d4d0fd (2026-08-11). Data as JSON: /api/errors/9fe2ff57d14a7b84. Report an issue: GitHub.

Appendix: source

Thrown at aiohttp/helpers.py:293

        if proxy.scheme in ("https", "wss"):
            client_logger.warning(
                "%s proxies %s are not supported, ignoring", proxy.scheme.upper(), proxy
            )
            continue
        if netrc_obj and auth is None:
            if proxy.host is not None:
                try:
                    auth = _auth_header_from_netrc(netrc_obj, proxy.host)
                except LookupError:
                    auth = None
        ret[proto] = ProxyInfo(proxy, auth)
    return ret


def get_env_proxy_for_url(url: URL) -> tuple[URL, str | None]:
    """Get a permitted proxy for the given URL from the env."""
    if url.host is not None and proxy_bypass(url.host):
        raise LookupError(f"Proxying is disallowed for `{url.host!r}`")

    proxies_in_env = proxies_from_env()
    try:
        proxy_info = proxies_in_env[url.scheme]
    except KeyError:
        raise LookupError(f"No proxies found for `{url!s}` in the env")
    else:
        return proxy_info.proxy, proxy_info.proxy_auth


@frozen_dataclass_decorator
class MimeType:
    type: str
    subtype: str
    suffix: str
    parameters: "MultiDictProxy[str]"

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