micropython/aiorepl: Initial version of an asyncio REPL.

This provides an async REPL with the following features:
- Run interactive REPL in the background.
- Execute statements using await.
- Simple history.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

micropython/aiorepl/README.md

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+# aiorepl
+
+This library provides "asyncio REPL", a simple REPL that can be used even
+while your program is running, allowing you to inspect program state, create
+tasks, and await asynchronous functions.
+
+This is inspired by Python's `asyncio` module when run via `python -m asyncio`.
+
+## Background
+
+The MicroPython REPL is unavailable while your program is running. This
+library runs a background REPL using the asyncio scheduler.
+
+Furthermore, it is not possible to `await` at the main REPL because it does
+not know about the asyncio scheduler.
+
+## Usage
+
+To use this library, you need to import the library and then start the REPL task.
+
+For example, in main.py:
+
+```py
+import uasyncio as asyncio
+import aiorepl
+
+async def demo():
+    await asyncio.sleep_ms(1000)
+    print("async demo")
+
+state = 20
+
+async def task1():
+    while state:
+        #print("task 1")
+        await asyncio.sleep_ms(500)
+    print("done")
+
+async def main():
+    print("Starting tasks...")
+
+    # Start other program tasks.
+    t1 = asyncio.create_task(task1())
+
+    # Start the aiorepl task.
+    repl = asyncio.create_task(aiorepl.task())
+
+    await asyncio.gather(t1, repl)
+
+asyncio.run(main())
+```
+
+The optional globals passed to `task([globals])` allows you to specify what
+will be in scope for the REPL. By default it uses `__main__`, which is the
+same scope as the regular REPL (and `main.py`). In the example above, the
+REPL will be able to call the `demo()` function as well as get/set the
+`state` variable.
+
+Instead of the regular `>>> ` prompt, the asyncio REPL will show `--> `.
+
+```
+--> 1+1
+2
+--> await demo()
+async demo
+--> state
+20
+--> import myapp.core
+--> state = await myapp.core.query_state()
+--> 1/0
+ZeroDivisionError: divide by zero
+--> def foo(x): return x + 1
+--> await asyncio.sleep(foo(3))
+--> 
+```
+
+History is supported via the up/down arrow keys.
+
+## Cancellation
+
+During command editing (the "R" phase), pressing Ctrl-C will cancel the current command and display a new prompt, like the regular REPL.
+
+While a command is being executed, Ctrl-C will cancel the task that is executing the command. This will have no effect on blocking code (e.g. `time.sleep()`), but this should be rare in an asyncio-based program.
+
+Ctrl-D at the asyncio REPL command prompt will terminate the current event loop, which will stop the running program and return to the regular REPL.
+
+## Limitations
+
+The following features are unsupported:
+
+* Tab completion is not supported (also unsupported in `python -m asyncio`).
+* Multi-line continuation. However you can do single-line definitions of functions, see demo above.
+* Exception tracebacks. Only the exception type and message is shown, see demo above.
+* Emacs shortcuts (e.g. Ctrl-A, Ctrl-E, to move to start/end of line).
+* Unicode handling for input.

micropython/aiorepl/aiorepl.py

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+# MIT license; Copyright (c) 2022 Jim Mussared
+
+import micropython
+import re
+import sys
+import time
+import uasyncio as asyncio
+
+# Import statement (needs to be global, and does not return).
+_RE_IMPORT = re.compile("^import ([^ ]+)( as ([^ ]+))?")
+_RE_FROM_IMPORT = re.compile("^from [^ ]+ import ([^ ]+)( as ([^ ]+))?")
+# Global variable assignment.
+_RE_GLOBAL = re.compile("^([a-zA-Z0-9_]+) ?=[^=]")
+# General assignment expression or import statement (does not return a value).
+_RE_ASSIGN = re.compile("[^=]=[^=]")
+
+# Command hist (One reserved slot for the current command).
+_HISTORY_LIMIT = const(5 + 1)
+
+
+async def execute(code, g, s):
+    if not code.strip():
+        return
+
+    try:
+        if "await " in code:
+            # Execute the code snippet in an async context.
+            if m := _RE_IMPORT.match(code) or _RE_FROM_IMPORT.match(code):
+                code = f"global {m.group(3) or m.group(1)}\n    {code}"
+            elif m := _RE_GLOBAL.match(code):
+                code = f"global {m.group(1)}\n    {code}"
+            elif not _RE_ASSIGN.search(code):
+                code = f"return {code}"
+
+            code = f"""
+import uasyncio as asyncio
+async def __code():
+    {code}
+
+__exec_task = asyncio.create_task(__code())
+"""
+
+            async def kbd_intr_task(exec_task, s):
+                while True:
+                    if ord(await s.read(1)) == 0x03:
+                        exec_task.cancel()
+                        return
+
+            l = {"__exec_task": None}
+            exec(code, g, l)
+            exec_task = l["__exec_task"]
+
+            # Concurrently wait for either Ctrl-C from the stream or task
+            # completion.
+            intr_task = asyncio.create_task(kbd_intr_task(exec_task, s))
+
+            try:
+                try:
+                    return await exec_task
+                except asyncio.CancelledError:
+                    pass
+            finally:
+                intr_task.cancel()
+                try:
+                    await intr_task
+                except asyncio.CancelledError:
+                    pass
+        else:
+            # Excute code snippet directly.
+            try:
+                try:
+                    micropython.kbd_intr(3)
+                    try:
+                        return eval(code, g)
+                    except SyntaxError:
+                        # Maybe an assignment, try with exec.
+                        return exec(code, g)
+                except KeyboardInterrupt:
+                    pass
+            finally:
+                micropython.kbd_intr(-1)
+
+    except Exception as err:
+        print(f"{type(err).__name__}: {err}")
+
+
+# REPL task. Invoke this with an optional mutable globals dict.
+async def task(g=None, prompt="--> "):
+    print("Starting asyncio REPL...")
+    if g is None:
+        g = __import__("__main__").__dict__
+    try:
+        micropython.kbd_intr(-1)
+        s = asyncio.StreamReader(sys.stdin)
+        # clear = True
+        hist = [None] * _HISTORY_LIMIT
+        hist_i = 0  # Index of most recent entry.
+        hist_n = 0  # Number of history entries.
+        c = 0  # ord of most recent character.
+        t = 0  # timestamp of most recent character.
+        while True:
+            hist_b = 0  # How far back in the history are we currently.
+            sys.stdout.write(prompt)
+            cmd = ""
+            while True:
+                b = await s.read(1)
+                c = ord(b)
+                pc = c  # save previous character
+                pt = t  # save previous time
+                t = time.ticks_ms()
+                if c < 0x20 or c > 0x7E:
+                    if c == 0x0A:
+                        # CR
+                        sys.stdout.write("\n")
+                        if cmd:
+                            # Push current command.
+                            hist[hist_i] = cmd
+                            # Increase history length if possible, and rotate ring forward.
+                            hist_n = min(_HISTORY_LIMIT - 1, hist_n + 1)
+                            hist_i = (hist_i + 1) % _HISTORY_LIMIT
+
+                            result = await execute(cmd, g, s)
+                            if result is not None:
+                                sys.stdout.write(repr(result))
+                                sys.stdout.write("\n")
+                        break
+                    elif c == 0x08 or c == 0x7F:
+                        # Backspace.
+                        if cmd:
+                            cmd = cmd[:-1]
+                            sys.stdout.write("\x08 \x08")
+                    elif c == 0x02:
+                        # Ctrl-B
+                        continue
+                    elif c == 0x03:
+                        # Ctrl-C
+                        if pc == 0x03 and time.ticks_diff(t, pt) < 20:
+                            # Two very quick Ctrl-C (faster than a human
+                            # typing) likely means mpremote trying to
+                            # escape.
+                            asyncio.new_event_loop()
+                            return
+                        sys.stdout.write("\n")
+                        break
+                    elif c == 0x04:
+                        # Ctrl-D
+                        sys.stdout.write("\n")
+                        # Shutdown asyncio.
+                        asyncio.new_event_loop()
+                        return
+                    elif c == 0x1B:
+                        # Start of escape sequence.
+                        key = await s.read(2)
+                        if key in ("[A", "[B"):
+                            # Stash the current command.
+                            hist[(hist_i - hist_b) % _HISTORY_LIMIT] = cmd
+                            # Clear current command.
+                            b = "\x08" * len(cmd)
+                            sys.stdout.write(b)
+                            sys.stdout.write(" " * len(cmd))
+                            sys.stdout.write(b)
+                            # Go backwards or forwards in the history.
+                            if key == "[A":
+                                hist_b = min(hist_n, hist_b + 1)
+                            else:
+                                hist_b = max(0, hist_b - 1)
+                            # Update current command.
+                            cmd = hist[(hist_i - hist_b) % _HISTORY_LIMIT]
+                            sys.stdout.write(cmd)
+                    else:
+                        # sys.stdout.write("\\x")
+                        # sys.stdout.write(hex(c))
+                        pass
+                else:
+                    sys.stdout.write(b)
+                    cmd += b
+    finally:
+        micropython.kbd_intr(3)

micropython/aiorepl/manifest.py

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+metadata(
+    version="0.1",
+    description="Provides an asynchronous REPL that can run concurrently with an asyncio, also allowing await expressions.",
+)
+
+module("aiorepl.py")