Implement heartbeats for Python

[unflxw]

Store global client and expose its config

Store the last (hopefully only) initialised client in a global
variable, and expose its config as a class method on the Client
class.

Implement AppSignal transmitter

Implement a transmitter module similar to the ones in other
integrations, which handles the sending of requests with the usual
AppSignal identifying params.

Remove empty TYPE_CHECKING block

Probably a leftover from some typing refactor.

Implement heartbeats for Python

Implement the heartbeats functionality for Python, similarly to how
it was implemented for Ruby, Elixir and Node.js.

Due to limitations on how with blocks are implemented, which make
it impossible for a function to behave in different ways when called
"by itself" and when called by a with block, it is possible to call
it in the following ways:

• heartbeat(name), which sends a finish heartbeat event
• heartbeat(name, function), which sends:
  • a start heartbeat event
  • a finish heartbeat event, if the function does not raise
• as a with Heartbeat(name): block (note: H not h!) which sends:
  • a start heartbeat event
  • a finish heartbeat event, if the with block does not raise

Add a LOGGING_ENDPOINT configuration variable to configure the
logging endpoint, which is also the endpoint to which heartbeats are
sent. This is a bit bizarre, as Python does not support the logging
feature yet, but it is consistent with our other integrations.

[tombruijn]

The build is failing because of some import error.

[unflxw]

Ended up changing the design significantly, please re-review. I feel that heartbeat_with_context was not a good name -- it was borrowed from send_error_with_context, but "with context" in that function means "with this context for the error", not "by using a with context block".

I feel that the current design, where the Heartbeat class implements the with context manager protocol, and heartbeat can optionally be called with a function (in a way, doing both the Ruby API design and the Elixir/Node.js API design) is a lot clearer, and likely to be a better fit to most use-cases.

Also fixed some major issues with the implementation.

[backlog-helper]

• This Pull Request needs more reviews. @luismiramirez @tombruijn - (More info)

---

This is a message from the daily scheduled checks.

New issue guide | Backlog management | Rules | Feedback