psf/requests · error · InvalidURL

Invalid URL {url!r}: No host supplied

Error message

Invalid URL {url!r}: No host supplied

What it means

An `InvalidURL` exception raised in `prepare_url` when the URL parses successfully and has a scheme, but the host component is empty. Without a host there is nothing to connect to, so the request cannot proceed. This catches malformed URLs like 'http://' or 'http:///path'.

Source

Thrown at src/requests/models.py:522

        # handles RFC 3986 only.
        if ":" in url and not url.lower().startswith("http"):
            self.url = url
            return

        # Support for unicode domain names and paths.
        try:
            scheme, auth, host, port, path, query, fragment = parse_url(url)
        except LocationParseError as e:
            raise InvalidURL(*e.args)

        if not scheme:
            raise MissingSchema(
                f"Invalid URL {url!r}: No scheme supplied. "
                f"Perhaps you meant https://{url}?"
            )

        if not host:
            raise InvalidURL(f"Invalid URL {url!r}: No host supplied")

        # In general, we want to try IDNA encoding the hostname if the string contains
        # non-ASCII characters. This allows users to automatically get the correct IDNA
        # behaviour. For strings containing only ASCII characters, we need to also verify
        # it doesn't start with a wildcard (*), before allowing the unencoded hostname.
        if not unicode_is_ascii(host):
            try:
                host = self._get_idna_encoded_host(host)
            except UnicodeError:
                raise InvalidURL("URL has an invalid label.")
        elif host.startswith(("*", ".")):
            raise InvalidURL("URL has an invalid label.")

        # Carefully reconstruct the network location
        netloc = auth or ""
        if netloc:
            netloc += "@"
        netloc += host

View on GitHub ↗ (pinned to 414f0513c3)

Solutions

1. Trace where the URL was built and ensure the hostname variable is non-empty — most often a missing env var or config value.
2. Validate config at startup: raise a clear error if the host setting is empty instead of letting it reach requests.
3. Print/log the exact URL being requested (it appears in the exception message via {url!r}) to spot the empty authority.

Example fix

# before
host = os.environ.get('API_HOST', '')
requests.get(f'http://{host}/health')

# after
host = os.environ['API_HOST']  # KeyError early if unset
if not host:
    raise RuntimeError('API_HOST is empty')
requests.get(f'http://{host}/health')

from urllib.parse import urlparse
parsed = urlparse(url)
if not parsed.netloc:
    raise ValueError(f"URL {url!r} has no host")

from requests.exceptions import InvalidURL
try:
    resp = requests.get(url)
except InvalidURL:
    ...  # e.g. 'http://' or 'http:///path' — reject or re-prompt for a real host
    raise

When it happens

Trigger: `requests.get('http://')`, `requests.get('http:///path')`, `requests.get('https://:8080/x')` — any URL where `parse_url` returns an empty host. Commonly produced by string formatting where the hostname variable is empty: `f'http://{host}/api'` with `host=''`.

Common situations: An unset environment variable or config key interpolated into a URL template (e.g. `API_HOST` empty in a container/CI environment), yielding 'http:///endpoint'; URL builders that accept optional host; accidental double slashes replacing the authority.

Related errors

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

AI-assisted analysis of psf/requests@414f0513c3 (2026-07-31). Data as JSON: /data/errors/e8fe13b5afb24b50.json. Report an issue: GitHub ↗.