py/modsys: Add optional sys.tracebacklimit attribute.

With behaviour as per CPython.

Signed-off-by: Damien George <damien@micropython.org>

3 files changed, 81 insertions, 2 deletions

diff --git a/tests/basics/sys_tracebacklimit.py b/tests/basics/sys_tracebacklimit.py
new file mode 100644
index 0000000000..1ee638967f
--- /dev/null
+++ b/tests/basics/sys_tracebacklimit.py
@@ -0,0 +1,78 @@
+# test sys.tracebacklimit
+
+try:
+    try:
+        import usys as sys
+        import uio as io
+    except ImportError:
+        import sys
+        import io
+except ImportError:
+    print("SKIP")
+    raise SystemExit
+
+try:
+    sys.tracebacklimit = 1000
+except AttributeError:
+    print("SKIP")
+    raise SystemExit
+
+if hasattr(sys, "print_exception"):
+    print_exception = sys.print_exception
+else:
+    import traceback
+
+    print_exception = lambda e, f: traceback.print_exception(None, e, sys.exc_info()[2], file=f)
+
+
+def print_exc(e):
+    buf = io.StringIO()
+    print_exception(e, buf)
+    s = buf.getvalue()
+    for l in s.split("\n"):
+        # Remove filename.
+        if l.startswith("  File "):
+            l = l.split('"')
+            print(l[0], l[2])
+        # uPy and CPy tracebacks differ in that CPy prints a source line for
+        # each traceback entry.  In this case, we know that offending line
+        # has 4-space indent, so filter it out.
+        elif not l.startswith("    "):
+            print(l)
+
+
+def f0():
+    raise ValueError("value")
+
+
+def f1():
+    f0()
+
+
+def f2():
+    f1()
+
+
+def f3():
+    f2()
+
+
+def ftop():
+    try:
+        f3()
+    except ValueError as er:
+        print_exc(er)
+
+
+ftop()
+
+for limit in range(4, -2, -1):
+    print("limit", limit)
+    sys.tracebacklimit = limit
+    ftop()
+
+
+# test deleting the attribute
+print(hasattr(sys, "tracebacklimit"))
+del sys.tracebacklimit
+print(hasattr(sys, "tracebacklimit"))
diff --git a/tests/run-tests.py b/tests/run-tests.py
index edd20b9bd5..dfe0a8e55f 100755
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -504,6 +504,7 @@ def run_tests(pyb, tests, args, result_dir, num_threads=1):
         skip_tests.add("basics/del_local.py")  # requires checking for unbound local
         skip_tests.add("basics/exception_chain.py")  # raise from is not supported
         skip_tests.add("basics/scope_implicit.py")  # requires checking for unbound local
+        skip_tests.add("basics/sys_tracebacklimit.py")  # requires traceback info
         skip_tests.add("basics/try_finally_return2.py")  # requires raise_varargs
         skip_tests.add("basics/unboundlocal.py")  # requires checking for unbound local
         skip_tests.add("extmod/uasyncio_event.py")  # unknown issue
diff --git a/tests/unix/extra_coverage.py.exp b/tests/unix/extra_coverage.py.exp
index 1a5a2cde85..67d299bca1 100644
--- a/tests/unix/extra_coverage.py.exp
+++ b/tests/unix/extra_coverage.py.exp
@@ -45,8 +45,8 @@ utime           utimeq
 argv            atexit          byteorder       exc_info
 exit            getsizeof       implementation  maxsize
 modules         path            platform        print_exception
-stderr          stdin           stdout          version
-version_info
+stderr          stdin           stdout          tracebacklimit
+version         version_info
 ementation
 # attrtuple
 (start=1, stop=2, step=3)