Understanding Python's PyAsyncMethods.am_send

· 326 words · 2 minute read

What is PyAsyncMethods.am_send? 🔗

PyAsyncMethods.am_send is a method in Python’s C API, specifically designed for asynchronous programming. It is part of the PyAsyncMethods structure, which defines a set of methods that an asynchronous iterator must implement. The am_send method is responsible for sending a value into an asynchronous generator.

How is PyAsyncMethods.am_send Used? 🔗

To understand the usage of PyAsyncMethods.am_send, let’s first look at a high-level overview of asynchronous generators in Python. An asynchronous generator is a function that yields values asynchronously, allowing for more efficient handling of I/O-bound tasks.

Here’s a simple example of an asynchronous generator in Python:

async def async_generator():
    yield 1
    yield 2
    yield 3

When using an asynchronous generator, you can send values back into it using the async_generator.asend(value) method. This is where PyAsyncMethods.am_send comes into play at a lower level.

How PyAsyncMethods.am_send Works 🔗

To grasp how PyAsyncMethods.am_send functions, it’s essential to understand the mechanics behind it. Think of an asynchronous generator as a conveyor belt that produces items (values) over time. The am_send method acts as a way to place an item back onto the conveyor belt, resuming its operation from where it last yielded a value.

When you call async_generator.asend(value), the following steps occur:

  1. Suspend Execution: The generator’s execution is paused at the last yield statement.
  2. Send Value: The value provided to asend(value) is sent back into the generator, essentially resuming its execution.
  3. Resume Execution: The generator continues its operation, using the sent value to proceed.

In the context of the C API, PyAsyncMethods.am_send is a function pointer within the PyAsyncMethods structure. It is invoked when a value is sent to an asynchronous generator from the Python level. Here’s a simplified conceptual representation in C:

typedef struct {
    PyObject *(*am_await)(PyObject *);
    PyObject *(*am_aiter)(PyObject *);
    PyObject *(*am_anext)(PyObject *);
    PyObject *(*am_send)(PyObject *, PyObject *); // am_send definition
} PyAsyncMethods;

When an asynchronous generator’s asend method is called, the am_send function is triggered, performing the value injection into the generator and resuming its execution.