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Keys

Note: This is not a lookup table of key objects provided by KMK. That listing can be found in keycodes.md. It's probably worth a look at the raw source if you're stumped: kmk/keys.py.

Key Objects

This is a bunch of documentation about how a physical keypress translates to events (and the lifecycle of said events) in KMK. It's somewhat technical, but if you're looking to extend your keyboard's functionality with extra code, you'll need at least some of this technical knowledge.

The first few steps in the process aren't all that interesting for most workflows, which is why they're buried deep in KMK: we scan a bunch of GPIO lanes (about as quickly as CircuitPython will let us) to see where, in a matrix of keys, a key has been pressed. The technical details about this process are probably best left to Wikipedia. Then, we scan through the defined keymap, finding the first valid key at this index based on the stack of currently active layers (this logic, if you want to read through the code, is in kmk/kmk_keyboard.py, method _find_key_in_map).

The next few steps are the interesting part, but to understand them, we need to understand a bit about what a Key object is (found in kmk/keys.py). Key objects have a few core pieces of information:

  • Their code, which can be any integer. Integers below FIRST_KMK_INTERNAL_KEY are sent through to the HID stack (and thus the computer, which will translate that integer to something meaningful - for example, code=4 becomes a on a US QWERTY/Dvorak keyboard).

  • Their attached modifiers (to implement things like shifted keys or KC.HYPR, which are single key presses sending along more than one key in a single HID report. For almost all purposes outside of KMK core, this field should be ignored - it can be safely populated through far more sane means than futzing with it by hand.

  • Handlers for "press" (sometimes known as "keydown") and "release" (sometimes known as "keyup") events. KMK provides handlers for standard keyboard functions and some special override keys (like KC.GESC, which is an enhanced form of existing ANSI keys) in kmk/handlers/stock.py.

  • A generic meta field, which is most commonly used for "argumented" keys - objects in the KC object which are actually functions that return Key instances, which often need to access the arguments passed into the "outer" function. Many of these examples are related to layer switching - for example, KC.MO is implemented as an argumented key - when the user adds KC.MO(1) to their keymap, the function call returns a Key object with meta set to an object containing layer and kc properties, for example. There's other uses for meta, and examples can be found in kmk/types.py

Key objects can also be chained together by calling them! To create a key which holds Control and Shift simultaneously, we can simply do:

CTRLSHFT = KC.LCTL(KC.LSFT)

keyboard.keymap = [ ... CTRLSHFT ... ]

When a key is pressed and we've pulled a Key object out of the keymap, the Key is first passed through the module processing pipeline. Modules can do whatever with that Key, but usually keys either pass right through, or are intercepted and emitted again later (think of timing based modules like Combos and Hold-Tap). Finally the assigned press handler will be run (most commonly, this is provided by KMK). On release the Key object lookup is, most of the time, cached and doesn't require searching the keymap again. Then it's the processing pipeline again, followed by the release handler.

Custom behavior can either be achieved with custom press and release handlers or with macros.

The Key Code Dictionary

You can also refer to a key by index:

  • KC['A']
  • KC['NO']
  • KC['LALT']

Or the KC.get function which has an optional default argument, which will be returned if the key is not found (default=None unless otherwise specified):

  • KC.get('A')
  • KC.get('NO', None)
  • KC.get('NOT DEFINED', KC.RALT)

Key names are case-sensitive. KC['NO'] is different from KC['no']. It is recommended that names are normally UPPER_CASE. The exception to this are alpha keys; KC['A'] and KC['a'] will both return the same, unshifted, key.