FAQs

On this page are some examples of usage and commonly asked questions.

Chaining transports

HTTPX Retries is implemented as a custom Transport. It's common to want to add additional custom behaviour (eg. rate-limiting, proxies and more), and it's possible to chain transports to layer in behaviours; the first argument to the RetryTransport constructor is a transport to wrap.

with AsyncClient(
    transport=RetryTransport(
        RateLimitTransport(
            AsyncHTTPTransport(),
            interval=timedelta(seconds=1),
            count=3,
        ),
        retry=Retry(total=5, backoff_factor=0.5),
    ),
    timeout=90.0,
) as client:
    ...

Client timeout or Retry timeout?

Does the httpx.Client timeout apply to each request made in a series of retries, or to the "user request", who wants the result in the next 10s, regardless of how many times the underlying HTTP client needs to try to get it?

The timeout passed to httpx.Client applies to each request in a series of retries. If a httpx.TimeoutException is raised and a retry is applicable, the same request, with the same timeout values, will be retried.

In the case where retries are bounded by individual (client) timeouts, it is always possible to work out the maximum possible time taken to execute all retries.

So if you wanted to add a lower overall retry value than the number of retries multiplied by the client timeout, you could tweak the max_backoff_wait and backoff_factor. Eg.

Retry(total=3, max_backoff_wait=5.0, backoff_factor=1, jitter=0)

would result in a retry-inclusive timeout of 15s + 3 * (client_timeout).

Limits / Cert / SSL / http2 parameters passed to the client are not being applied

This is a limitation of the way transports are applied to clients in HTTPX. If you provide a custom transport, several parameters that can be passed to httpx.Client are ignored. The workaround is to directly provide an instance of httpx.HTTPTransport (or the async variant) which will accept these parameters.

with Client(
    transport=RetryTransport(
        HTTPTransport(
            # Pass a transport with these parameters to wrap.
            http2=True,
            limits=httpx.Limits(max_connections=100, max_keepalive_connections=100, keepalive_expiry=60),
            verify=False
        ),
        retry=Retry(total=5, backoff_factor=0.5),
    )
    # These will do nothing!
    http2=True,
    limits=httpx.Limits(max_connections=100, max_keepalive_connections=100, keepalive_expiry=60),
    verify=False
) as client:
    ...