psf/requests · error · InvalidSchema

No connection adapters were found for {url!r}

Error message

No connection adapters were found for {url!r}

What it means

Raised as `requests.exceptions.InvalidSchema` from `Session.get_adapter()` in `src/requests/sessions.py:881`. A Session dispatches each URL to a transport adapter chosen by longest matching prefix; by default only 'http://' and 'https://' adapters are mounted. If the request URL matches no mounted prefix (unknown scheme, missing scheme, or a typo), there is no transport capable of sending it.

Source

Thrown at src/requests/sessions.py:881

        proxies = merge_setting(proxies, self.proxies)
        stream = merge_setting(stream, self.stream)
        verify = merge_setting(verify, self.verify)
        cert = merge_setting(cert, self.cert)

        return {"proxies": proxies, "stream": stream, "verify": verify, "cert": cert}

    def get_adapter(self, url: str) -> BaseAdapter:
        """
        Returns the appropriate connection adapter for the given URL.

        :rtype: requests.adapters.BaseAdapter
        """
        for prefix, adapter in self.adapters.items():
            if url.lower().startswith(prefix.lower()):
                return adapter

        # Nothing matches :-/
        raise InvalidSchema(f"No connection adapters were found for {url!r}")

    def close(self) -> None:
        """Closes all adapters and as such the session"""
        for v in self.adapters.values():
            v.close()

    def mount(self, prefix: str, adapter: BaseAdapter) -> None:
        """Registers a connection adapter to a prefix.

        Adapters are sorted in descending order by prefix length.
        """
        self.adapters[prefix] = adapter
        keys_to_move = [k for k in self.adapters if len(k) < len(prefix)]

        for key in keys_to_move:
            self.adapters[key] = self.adapters.pop(key)

    def __getstate__(self) -> dict[str, Any]:

View on GitHub ↗ (pinned to 414f0513c3)

Solutions

1. Add the scheme: use 'https://example.com/path'; the repr in the message shows the exact URL requests saw — check it for missing scheme, typos, whitespace, or quote characters.
2. If the URL comes from config, normalize it: `url if url.startswith(('http://','https://')) else 'https://' + url`.
3. For non-HTTP schemes, mount an adapter that supports them (e.g. `requests_file.FileAdapter` for file://) or use the appropriate library (ftplib, websockets).
4. Strip stray characters: `url.strip().strip('\'"')` before requesting.

Example fix

# before
base = os.environ['API_HOST']  # 'api.example.com'
requests.get(f'{base}/v1/items')
# after
base = os.environ['API_HOST']
if not base.startswith(('http://', 'https://')):
    base = 'https://' + base
requests.get(f'{base}/v1/items')

def has_adapter(session, url):
    return any(url.lower().startswith(prefix) for prefix in session.adapters)

if not has_adapter(session, url):
    raise ValueError(f'No adapter mounted for {url!r} — expected http:// or https://')

try:
    resp = session.get(url)
except requests.exceptions.InvalidSchema as e:
    # scheme like ftp://, file://, ws:// or a missing scheme entirely
    log.error('Unsupported URL scheme: %s', e)

When it happens

Trigger: Calling `requests.get('example.com/path')` (no scheme), a typo like 'htp://' or 'https:/', a non-HTTP scheme such as 'ftp://', 'file://', 'ws://', 'localhost:8000/api' (parsed as scheme 'localhost'), or a URL with leading whitespace/quotes so the prefix match fails.

Common situations: URLs from config files or env vars stored without the scheme; concatenation bugs producing double or missing slashes; pasting a URL wrapped in quotes; expecting requests to fetch file:// or ftp:// resources (unsupported without a third-party adapter like requests-file/requests-ftp); base-URL joining that drops the scheme.

Related errors

• Invalid URL {url!r}: No scheme supplied. Perhaps you meant h
• Invalid URL {url!r}: No host supplied
• URL has an invalid label.
• Invalid percent-escape sequence: '{h}'
• Files must be provided.

AI-assisted analysis of psf/requests@414f0513c3 (2026-07-31). Data as JSON: /data/errors/8b7d06f4fad34a22.json. Report an issue: GitHub ↗.