httpx._client.UseClientDefault

For some parameters such as auth=... and timeout=... we need to be able to indicate the default "unset" state, in a way that is distinctly different to using None.

The default "unset" state indicates that whatever default is set on the client should be used. This is different to setting None, which explicitly disables the parameter, possibly overriding a client default.

For example we use timeout=USE_CLIENT_DEFAULT in the request() signature. Omitting the timeout parameter will send a request using whatever default timeout has been configured on the client. Including timeout=None will ensure no timeout is used.

Note that user code shouldn't need to use the USE_CLIENT_DEFAULT constant, but it is used internally when a parameter is not included.