Merged revisions 67117-67119,67123-67124,67143 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/trunk

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  r67117 | georg.brandl | 2008-11-06 11:17:58 +0100 (Thu, 06 Nov 2008) | 2 lines

  #4268: Use correct module for two toplevel functions.
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  r67118 | georg.brandl | 2008-11-06 11:19:11 +0100 (Thu, 06 Nov 2008) | 2 lines

  #4267: small fixes in sqlite3 docs.
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  r67119 | georg.brandl | 2008-11-06 11:20:49 +0100 (Thu, 06 Nov 2008) | 2 lines

  #4245: move Thread section to the top.
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  r67123 | georg.brandl | 2008-11-06 19:49:15 +0100 (Thu, 06 Nov 2008) | 2 lines

  #4247: add "pass" examples to tutorial.
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  r67124 | andrew.kuchling | 2008-11-06 20:23:02 +0100 (Thu, 06 Nov 2008) | 1 line

  Fix grammar error; reword two paragraphs
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  r67143 | georg.brandl | 2008-11-07 09:27:39 +0100 (Fri, 07 Nov 2008) | 2 lines

  Fix syntax.
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1 files changed, 35 insertions, 0 deletions

diff --git a/Doc/tutorial/controlflow.rst b/Doc/tutorial/controlflow.rst
index 5fdddcb..2a55cf1 100644
--- a/Doc/tutorial/controlflow.rst
+++ b/Doc/tutorial/controlflow.rst
@@ -196,6 +196,41 @@ required syntactically but the program requires no action. For example::
    ...     pass  # Busy-wait for keyboard interrupt (Ctrl+C)
    ... 
 
+This is commonly used for creating minimal classes such as exceptions, or
+for ignoring unwanted exceptions::
+
+   >>> class ParserError(Exception):
+   ...     pass
+   ... 
+   >>> try:
+   ...     import audioop
+   ... except ImportError:
+   ...     pass
+   ... 
+
+Another place :keyword:`pass` can be used is as a place-holder for a function or
+conditional body when you are working on new code, allowing you to keep
+thinking at a more abstract level.  However, as :keyword:`pass` is silently
+ignored, a better choice may be to raise a :exc:`NotImplementedError`
+exception::
+
+   >>> def initlog(*args):
+   ...     raise NotImplementedError   # Open logfile if not already open
+   ...     if not logfp:
+   ...         raise NotImplementedError  # Set up dummy log back-end
+   ...     raise NotImplementedError('Call log initialization handler')
+   ... 
+
+If :keyword:`pass` were used here and you later ran tests, they may fail
+without indicating why.  Using :exc:`NotImplementedError` causes this code
+to raise an exception, telling you exactly where the incomplete code 
+is.  Note the two calling styles of the exceptions above.
+The first style, with no message but with an accompanying comment, 
+lets you easily leave the comment when you remove the exception,
+which ideally would be a good description for
+the block of code the exception is a placeholder for.  However, the 
+third example, providing a message for the exception, will produce 
+a more useful traceback.
 
 .. _tut-functions: