Changes between Version 3 and Version 4 of python2and3CompatiblityEN

Timestamp:

Jun 13, 2013, 1:04:52 AM (12 years ago)

Author:

Martin Kolman

Comment:

--

python2and3CompatiblityEN

@@ -5 +5 @@
 
 == Exception handling ==
+The main difficulty in writing code that is both Python 2 and 3 compatible is getting to the exception object.
+
+The ''old'' syntax that works in all recent Python 2 (at least 2.5-2.7) versions looks like this:
+{{{
+except Exception, e:
+}}}
+The variable ''e'' contains the exception that occurred. This syntax is not supported by Python 3.
+
+An alternative syntax is supported in Python 2.6, 2.7 and all Python 3 versions:
+{{{
+except Exception as e:
+}}}
+Again, ''e'' contains the exception object.
+
+As long as Python 2.5 needs to be supported, this is a problem, as Python 2.5 does not support the new ''as'' notation and Python 3 on the other hand does not support the old ''comma'' notation.
+
+Fortunately, there is a workaround:
+
+{{{
+except Exception:
+    e = sys.exc_info()[1]
+}}}
+
+or alternatively for easy find & replace a standalone version independent on external imports:
+
+{{{
+except Exception:
+    import sys
+    e = sys.exc_info()[1]
+}}}
+
+This piece of code might look weird, but works in Python 2.5 - 3.3+
+
+If Python 2.5 doesn't have to be supported, just using the ''as'' syntax is enough for the exception handling code to be Python 2.6-3.3+ compatible.
 
 == Unicode handling ==