PyObjC CoreMIDI Framework

Warnings

• breaking Python 3.9 support was dropped in PyObjC 12.0. Python 3.8 support was dropped in PyObjC 11.0. The current version requires Python >= 3.10.
  Fix: Ensure your Python environment is 3.10 or newer.
• gotcha CoreMIDI bindings are a low-level API, and for certain interactions, especially those not based on CoreFoundation or Objective-C types, users may need to perform manual reference counting. Some C functions like `MIDIDeviceCreate`, `MIDISend`, and event list manipulation (`MIDIEventListAdd`, `MIDIEventListInit`) are noted as requiring manual bindings or not being available from Python.
  Fix: Consult the PyObjC API Notes for CoreMIDI and Apple's CoreMIDI C API documentation for detailed usage and limitations.
• breaking PyObjC 11.1 aligned the core bridge's behavior with `clang`'s documentation for Automatic Reference Counting (ARC) regarding initializer methods. Methods in the 'init' family now correctly steal a reference to self and return a new reference, which differs from previous PyObjC versions' handling of partially initialized objects.
  Fix: Review custom Python subclasses of Objective-C classes, particularly `__new__` and `__init__` methods, to ensure compatibility with ARC behavior for initializers. Refer to `__init__` related breaking changes from v10.3/v10.3.1.
• gotcha Experimental support for free-threading (PEP 703) introduced in Python 3.13 is included in PyObjC 11, but PyObjC 10.3 explicitly did not support it. While PyObjC 12.1 supports Python 3.10+, if targeting Python 3.13 with free-threading, be aware of the experimental nature of this support.
  Fix: Exercise caution and thorough testing when using PyObjC with experimental free-threading builds of Python 3.13 or newer. Stick to default Python builds for stable applications.
• gotcha The behavior of `__init__` when a user implements `__new__` in Objective-C bridged classes changed in PyObjC 10.3 (dropping support for `__init__` in such cases) and was partially reintroduced in 10.3.1 due to breaking popular projects.
  Fix: If encountering issues with `__init__` not being called after `__new__`, ensure you are on PyObjC 10.3.1 or later, and review the specific conditions under which `__init__` is supported when `__new__` is user-implemented versus provided by PyObjC.

Install

• pip install pyobjc-framework-coremidi Install PyObjC CoreMIDI

Imports

• CoreMIDI

  import CoreMIDI

• MIDIObjectGetStringProperty

  from CoreMIDI import MIDIObjectGetStringProperty

Quickstart

This example demonstrates how to import the CoreMIDI framework and iterate through the available MIDI devices, printing their names. CoreMIDI is a low-level API; more complex interactions often require a deeper understanding of its C API and manual resource management.

import CoreMIDI
import objc

def list_midi_devices():
    """Lists all available CoreMIDI devices."""
    print("MIDI Devices:")
    num_devices = CoreMIDI.MIDIGetNumberOfDevices()
    if num_devices == 0:
        print("  No MIDI devices found.")
        return

    for i in range(num_devices):
        midi_device_ref = CoreMIDI.MIDIGetDevice(i)
        if midi_device_ref:
            # MIDIObjectGetStringProperty returns a status code and the string value.
            # PyObjC automatically bridges CFStringRef to Python string.
            (name_result, name_str) = CoreMIDI.MIDIObjectGetStringProperty(
                midi_device_ref, CoreMIDI.kMIDIPropertyName
            )
            if name_result == 0: # noErr
                print(f"  Device {i}: {name_str}")
            else:
                print(f"  Device {i}: (Error getting name, code {name_result})")
        else:
            print(f"  Device {i}: (Could not get device reference)")

if __name__ == "__main__":
    list_midi_devices()