micropython — access and control MicroPython internals

Functions

micropython.const(expr: int) → int

Used to declare that the expression is a constant so that the compiler can optimise it. The use of this function should be as follows:

from micropython import const

CONST_X = const(123)
CONST_Y = const(2 * CONST_X + 1)

Constants declared this way are still accessible as global variables from outside the module they are declared in. On the other hand, if a constant begins with an underscore then it is hidden, it is not available as a global variable, and does not take up any memory during execution.

This const function is recognised directly by the MicroPython parser and is provided as part of the micropython module mainly so that scripts can be written which run under both CPython and MicroPython, by following the above pattern.

micropython.opt_level(level: int | None = None) → int | None

If level is given then this function sets the optimisation level for subsequent compilation of scripts, and returns None. Otherwise it returns the current optimisation level.

The optimisation level controls the following compilation features:

  • Assertions: at level 0 assertion statements are enabled and compiled into the bytecode; at levels 1 and higher assertions are not compiled.

  • Built-in __debug__ variable: at level 0 this variable expands to True; at levels 1 and higher it expands to False.

  • Source-code line numbers: at levels 0, 1 and 2 source-code line number are stored along with the bytecode so that exceptions can report the line number they occurred at; at levels 3 and higher line numbers are not stored.

The default optimisation level is usually level 0.

micropython.alloc_emergency_exception_buf(size: int) → None

Allocate size bytes of RAM for the emergency exception buffer (a good size is around 100 bytes). The buffer is used to create exceptions in cases when normal RAM allocation would fail (eg within an interrupt handler) and therefore give useful traceback information in these situations.

A good way to use this function is to put it at the start of your main script (eg boot.py or main.py) and then the emergency exception buffer will be active for all the code following it.

micropython.mem_info(verbose: Any | None = None) → None

Print information about currently used memory. If the verbose argument is given then extra information is printed.

The information that is printed is implementation dependent, but currently includes the amount of stack and heap used. In verbose mode it prints out the entire heap indicating which blocks are used and which are free.

micropython.qstr_info(verbose: Any | None = None) → None

Print information about currently interned strings. If the verbose argument is given then extra information is printed.

The information that is printed is implementation dependent, but currently includes the number of interned strings and the amount of RAM they use. In verbose mode it prints out the names of all RAM-interned strings.

micropython.stack_use() → int

Return an integer representing the current amount of stack that is being used. The absolute value of this is not particularly useful, rather it should be used to compute differences in stack usage at different points.

micropython.heap_lock() → None

Lock the heap. While locked, no memory allocation can occur and a MemoryError will be raised if any heap allocation is attempted.

Locks nest: calling heap_lock() multiple times increases the lock depth. The heap remains locked until heap_unlock() has been called the same number of times.

If the REPL becomes active with the heap locked then it will be forcefully unlocked.

micropython.heap_unlock() → int

Decrement the heap lock depth by one and return the new depth as a non-negative integer. A return value of 0 means the heap is no longer locked and allocations are once again permitted.

micropython.heap_locked() → int

Return the current heap lock depth as a non-negative integer; 0 means the heap is not locked.

Note: this function is not available on the OpenMV Cam.

micropython.kbd_intr(chr: int) → None

Set the character that will raise a KeyboardInterrupt exception. By default this is set to 3 during script execution, corresponding to Ctrl-C. Passing -1 to this function will disable capture of Ctrl-C, and passing 3 will restore it.

This function can be used to prevent the capturing of Ctrl-C on the incoming stream of characters that is usually used for the REPL, in case that stream is used for other purposes.

micropython.schedule(func: Callable[[Any], Any], arg: Any) → None

Schedule the function func to be executed “very soon”. The function is passed the value arg as its single argument. “Very soon” means that the MicroPython runtime will do its best to execute the function at the earliest possible time, given that it is also trying to be efficient, and that the following conditions hold:

  • A scheduled function will never preempt another scheduled function.

  • Scheduled functions are always executed “between opcodes” which means that all fundamental Python operations (such as appending to a list) are guaranteed to be atomic.

  • A given port may define “critical regions” within which scheduled functions will never be executed. Functions may be scheduled within a critical region but they will not be executed until that region is exited. An example of a critical region is a preempting interrupt handler (an IRQ).

  • Inside native code functions, scheduled functions are not called unless the native code calls a function that specifically does so.

  • Certain functions including poll.poll, poll.ipoll, time.sleep and time.sleep_ms (including zero-duration sleeps) will call scheduled functions.

A use for this function is to schedule a callback from a preempting IRQ. Such an IRQ puts restrictions on the code that runs in the IRQ (for example the heap may be locked) and scheduling a function to call later will lift those restrictions.

On multi-threaded ports, the scheduled function’s behaviour depends on whether the Global Interpreter Lock (GIL) is enabled for the specific port:

  • If GIL is enabled, the function can preempt any thread and run in its context.

  • If GIL is disabled, the function will only preempt the main thread and run in its context.

Note: If schedule() is called from a preempting IRQ, when memory allocation is not allowed and the callback to be passed to schedule() is a bound method, passing this directly will fail. This is because creating a reference to a bound method causes memory allocation. A solution is to create a reference to the method in the class constructor and to pass that reference to schedule(). This is discussed in detail here reference documentation under “Creation of Python objects”.

There is a finite queue to hold the scheduled functions and schedule() will raise a RuntimeError if the queue is full.

Classes

class micropython.RingIO(size: int)
class micropython.RingIO(buffer: bytes | bytearray | memoryview)

Provides a fixed-size ringbuffer for bytes with a stream interface. Can be considered a FIFO-queue variant of io.BytesIO. The two constructor forms differ only in how the backing buffer is supplied:

  • RingIO(size) allocates the backing buffer internally. The classic ringbuffer algorithm reserves one byte for tracking, so the allocated buffer is one byte larger than size and the instance can hold the full size bytes of data. For example, RingIO(16) allocates a 17-byte buffer and holds 16 bytes of data.

  • RingIO(buffer) uses the supplied buffer in place rather than allocating one. Because one byte is reserved for tracking, the instance can hold len(buffer) - 1 bytes of data. For example, RingIO(bytearray(16)) holds 15 bytes of data.

A RingIO instance is IRQ-/thread-safe when used to pass data in a single direction (for example written to from an IRQ and read from a non-IRQ function, or vice versa). This does not hold if a single instance is written to from both IRQ and non-IRQ contexts, which would often cause data corruption.

any() → int

Returns an integer counting the number of characters that can be read.

read(nbytes: int | None = None) → bytes

Read available characters. This is a non-blocking function. If nbytes is specified then read at most that many bytes, otherwise read as much data as possible.

Return value: a bytes object containing the bytes read. Will be zero-length bytes object if no data is available.

readline(nbytes: int | None = None) → bytes

Read a line, ending in a newline character or return if one exists in the buffer, else return available bytes in buffer. If nbytes is specified then read at most that many bytes.

Return value: a bytes object containing the line read.

readinto(buf: bytearray | memoryview, nbytes: int | None = None) → int

Read available bytes into the provided buf. If nbytes is specified then read at most that many bytes. Otherwise, read at most len(buf) bytes.

Return value: Integer count of the number of bytes read into buf.

write(buf: bytes | bytearray | memoryview) → int

Non-blocking write of bytes from buf into the ringbuffer, limited by the available space in the ringbuffer.

Return value: Integer count of bytes written.

close() → None

No-op provided as part of standard stream interface. Has no effect on data in the ringbuffer.