arduino/Arduino · error · ValueError

You can only send PreparedRequests.

Error message

You can only send PreparedRequests.

What it means

Session.send() only accepts PreparedRequest objects. If the passed object still has a .prepare attribute (i.e. it's an unprepared requests.Request), send raises ValueError, guarding against the common mistake of passing a plain Request.

Source

Thrown at arduino-core/src/processing/app/i18n/python/requests/sessions.py:398

        """

        return self.request('PATCH', url,  data=data, **kwargs)

    def delete(self, url, **kwargs):
        """Sends a DELETE request. Returns :class:`Response` object.

        :param url: URL for the new :class:`Request` object.
        :param \*\*kwargs: Optional arguments that ``request`` takes.
        """

        return self.request('DELETE', url, **kwargs)

    def send(self, request, **kwargs):
        """Send a given PreparedRequest."""
        # It's possible that users might accidentally send a Request object.
        # Guard against that specific failure case.
        if getattr(request, 'prepare', None):
            raise ValueError('You can only send PreparedRequests.')

        # Set up variables needed for resolve_redirects and dispatching of
        # hooks
        allow_redirects = kwargs.pop('allow_redirects', True)
        req = kwargs.pop('req', None)
        stream = kwargs.get('stream', False)
        timeout = kwargs.get('timeout')
        verify = kwargs.get('verify')
        cert = kwargs.get('cert')
        proxies = kwargs.get('proxies')
        hooks = request.hooks

        # Get the appropriate adapter to use
        adapter = self.get_adapter(url=request.url)

        # Start time (approximately) of the request
        start = datetime.utcnow()
        # Send the request

View on GitHub (pinned to a0df6e0e83)

Solutions

1. Call .prepare() on the Request before sending, or use session.request(...) which prepares for you.
2. Use requests.PreparedRequest() explicitly and populate prepared fields before send().
3. Fix wrapper functions to accept PreparedRequest or call prepare internally.

Example fix

// before
req = requests.Request('GET', 'https://example.com')
session.send(req)  # ValueError
// after
req = requests.Request('GET', 'https://example.com').prepare()
session.send(req)

from requests import PreparedRequest
def send_prepared(session, req, **kw):
    if not isinstance(req, PreparedRequest):
        raise TypeError('send() requires PreparedRequest, got %s' % type(req).__name__)
    return session.send(req, **kw)

from requests import PreparedRequest
def is_prepared(req) -> bool:
    return isinstance(req, PreparedRequest)

try:
    session.send(req, timeout=10)
except ValueError as e:
    if 'PreparedRequests' in str(e):
        req = req.prepare()
        session.send(req, timeout=10)
    else:
        raise

When it happens

Trigger: Calling session.send(request.Request(...)) directly; building a Request manually and forgetting to call Request.prepare() / requests.PreparedRequest; passing the wrong object through wrapper code that forwards to session.send().

Common situations: Low-level usage of requests internals (retry middleware, custom adapters) where authors mix Request and PreparedRequest; copying example code that uses session.send without the preparation step.

Understand the failure class

Background: "Must be a positive integer", "Invalid value", "Unsupported": the invalid-argument-value error family, when a library rejects the value you pass — this error's family across 35 libraries.

Related errors

• cannot encode objects that are not 2-tuples
• Classes extending RequestMethods must implement their own ``
• stream_decompress mode must be gzip or deflate
• SSLError(e)
• MaxRetryError(self, url, e)

AI-assisted analysis of arduino/Arduino@a0df6e0e83 (2026-09-06). Data as JSON: /api/errors/4314081b81e1eb76. Report an issue: GitHub.