X-Git-Url: https://arthur.barton.de/gitweb/?a=blobdiff_plain;f=CODINGSTYLE;h=348a2f51340bfe3545b7f9477cde631343126e7c;hb=8ab02ae782a1bc6e28cd0719d66c8ae51920ade0;hp=12879e56b1873f06264aaa6d54021d78dc139f9b;hpb=6b9a8dc93e462c93408848470e3552ed10a5cce4;p=bup.git

diff --git a/CODINGSTYLE b/CODINGSTYLE
index 12879e5..348a2f5 100644
--- a/CODINGSTYLE
+++ b/CODINGSTYLE
@@ -1,7 +1,14 @@
 .. -*-rst-*-
 
-General
-=======
+C
+=
+
+The C implementations should follow the `kernel/git coding style
+<http://www.kernel.org/doc/Documentation/CodingStyle>`_.
+
+
+Python
+======
 
 Python code follows `PEP8 <http://www.python.org/dev/peps/pep-0008/>`_
 with regard to coding style and `PEP257
@@ -23,5 +30,56 @@ blank line in between). Here's an example from
 Module-level docstrings follow exactly the same guidelines but without the
 blank line between the summary and the details.
 
-The C implementations should follow the `kernel/git coding style
-<http://www.kernel.org/doc/Documentation/CodingStyle>`_.
+
+Exception Handling
+------------------
+
+Avoid finally: blocks in favor of explict catches because a throw
+from a finally block will lose any pending exception.  An explicit
+catch can chain it (see below).
+
+To behave similarly under Python 2 and 3, use add_ex_tb() to
+explicitly add stack traces to any exceptions that are going to be
+re-raised by anything other than a no-argument raise (otherwise the
+stack trace will be lost)::
+
+  try:
+      ...
+  except ... as ex:
+      add_ex_tb(ex)
+      pending_ex = ex
+  ...
+  raise pending_ex
+
+When an exception is thrown from an exception handler, the pending
+exception should be the `"context"
+<https://docs.python.org/3/reference/simple_stmts.html#the-raise-statement>`_
+of the new exception, which can be accomplished (portably) via
+``pending_raise()``::
+
+  try:
+      ...
+  except ... as ex:
+      with pending_raise(ex):
+          clean_up()
+
+This should do roughly the same thing in Python 2 and Python 3,
+throwing any exception from ``clean_up()`` after adding ex as the
+``__context__`` if clean_up() throws, and throwing ``ex`` otherwise.
+
+If for some reason, you need more control, you can use
+``add_ex_ctx()`` directly::
+
+  try:
+      ...
+  except ... as ex:
+      add_ex_tb(ex)
+      try:
+          ...
+      except ... as ex2:
+          add_ex_tb(ex2)
+          raise add_ex_ctx(ex2, ex)
+      raise
+
+See the end of ``lib/bup/compat.py`` for a functional example, and all
+of this can be removed once we drop support for Python 2.