chore: make traceback module optional

some boards don't provide traceback so we can add a minimal implementation
that works _good enough_ in those cases so asyncio can still be used

Author: imnotjames

asyncio/core.py

@@ -16,7 +16,12 @@
 """
 
 from adafruit_ticks import ticks_ms as ticks, ticks_diff, ticks_add
-import sys, select, traceback
+import sys, select
+
+try:
+    from traceback import print_exception
+except:
+    from .traceback import print_exception
 
 # Import TaskQueue and Task, preferring built-in C code over Python code
 try:
@@ -371,7 +376,7 @@ def default_exception_handler(loop, context):
         """The default exception handler that is called."""
 
         exc = context["exception"]
-        traceback.print_exception(None, exc, exc.__traceback__)
+        print_exception(None, exc, exc.__traceback__)
 
     def call_exception_handler(context):
         """Call the current exception handler. The argument *context* is passed through

asyncio/traceback.py

@@ -0,0 +1,48 @@
+try:
+    from typing import List
+except ImportError:
+    pass
+
+import sys
+
+
+def _print_err(*args):
+    print(*args, file=sys.stderr)
+
+
+def _print_traceback(traceback, limit=None) -> List[str]:
+    if limit is None:
+        if hasattr(sys, "tracebacklimit"):
+            limit = sys.tracebacklimit
+
+    n = 0
+    while traceback is not None:
+        frame = traceback.tb_frame
+        line_number = traceback.tb_lineno
+        frame_code = frame.f_code
+        filename = frame_code.co_filename
+        name = frame_code.co_name
+        _print_err('  File "%s", line %d, in %s' % (filename, line_number, name))
+        traceback = traceback.tb_next
+        n = n + 1
+        if limit is not None and n >= limit:
+            break
+
+
+def print_exception(exception, value, traceback):
+    if traceback:
+        _print_err("Traceback (most recent call last):")
+        _print_traceback(traceback)
+
+    if isinstance(exception, Exception) or isinstance(exception, BaseException):
+        exception_type = type(exception).__name__
+    elif hasattr(exception, "__name__"):
+        exception_type = exception.__name__
+    else:
+        exception_type = type(value).__name__
+
+    valuestr = str(value)
+    if value is None or not valuestr:
+        _print_err(exception_type)
+    else:
+        _print_err("%s: %s" % (str(exception_type), valuestr))