Adds examples of Exceptions.

Author: paulross

Beginers/ExampleExceptions/A_traceback.py

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+#!/usr/bin/env python
+"""Example of raising an exception through a call chain.
+
+Created on Aug 19, 2011
+
+@author: paulross
+"""
+
+def a():
+    b()
+    
+def b():
+    c()
+
+def c():
+    raise Exception('Ouch')
+
+def main():
+    a()
+    
+if __name__ == '__main__':
+    main()

Beginers/ExampleExceptions/B_catch.py

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+#!/usr/bin/env python
+"""Example of raising an exception through a call chain.
+Function c() will randomly raise a type ExceptionOne or ExceptionTwo. These
+will be caught by a() and b() respectively.
+
+Created on Aug 19, 2011
+
+@author: paulross
+"""
+
+import random
+
+class ExceptionOne(Exception):
+    pass
+
+class ExceptionTwo(Exception):
+    pass
+
+def a():
+    try:
+        b()
+        print('  a() called b() with no exception raised')
+    except ExceptionOne as err:
+        print('  a() CAUGHT %s' % err)
+    
+def b():
+    try:
+        c()
+    except ExceptionTwo as err:
+        print('  b() CAUGHT %s' % err)
+    else:
+        print('  b() No exception raised')
+
+def c():
+    # randVal is (0, 1, 2)
+    randVal = random.randint(0, 2)
+    if randVal == 1:
+        raise ExceptionOne('I am the One')
+    elif randVal == 2:
+        raise ExceptionTwo('I am the One two')
+    # Do something. Hopefully its useful.
+
+def main():
+    for i in range(8):
+        print('Round %d:' % i)
+        a()
+    return 0
+
+if __name__ == '__main__':
+    main()

Beginers/ExampleExceptions/C_finally_.py

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+#!/usr/bin/env python
+"""Example of raising an exception where b() has a finally clause and a()
+catches the exception.
+
+Created on Aug 19, 2011
+
+@author: paulross
+"""
+
+class ExceptionNormal(Exception):
+    pass
+
+class ExceptionCleanUp(Exception):
+    pass
+
+def a():
+    try:
+        b()
+    except ExceptionNormal as err:
+        print('  a(): CAUGHT "%s"' % err)
+    
+def b():
+    try:
+        c()
+    finally:
+        print('  b(): finally: This code is always executed.')
+
+def c():
+    print('Raising "ExceptionNormal" from c()')
+    raise ExceptionNormal('ExceptionNormal raised from function c()')
+
+def main():
+    a()
+    return 0
+
+if __name__ == '__main__':
+    main()

Beginers/ExampleExceptions/C_finally_prob.py

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+#!/usr/bin/env python
+"""Illustrates the problem where a finally block raises an exception. This
+can mask the original exception that caused the problem in the first place.
+
+The user sees the ExceptionCleanUp but not the ExceptionNormal which was masked
+(in Python 2.x). Python 3 reports both exceptions.
+
+Created on Aug 19, 2011
+
+@author: paulross
+"""
+
+class ExceptionNormal(Exception):
+    pass
+
+class ExceptionCleanUp(Exception):
+    pass
+
+def a():
+    b()
+    
+def b():
+    try:
+        c()
+    finally:
+        print('  b(): finally: This code is always executed.')
+        cleanUp()
+
+def c():
+    print('Raising "ExceptionNormal" from c()')
+    raise ExceptionNormal('ExceptionNormal raised from function c()')
+
+def cleanUp():
+    raise ExceptionCleanUp('Can not clean up')
+
+def main():
+    a()
+    return 0
+
+if __name__ == '__main__':
+    main()

Beginers/ExampleExceptions/C_finally_soln.py

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+#!/usr/bin/env python
+"""Illustrates one possible solution to the problem where a finally block raises
+an exception.
+
+Created on Aug 19, 2011
+
+@author: paulross
+"""
+
+class ExceptionNormal(Exception):
+    pass
+
+class ExceptionCleanUp(Exception):
+    pass
+
+def a():
+    b()
+    
+def b():
+    try:
+        c()
+    finally:
+        # If doing something that might raise then trap this exception
+        # to preserve the original one (if any).
+        try:
+            print('  b(): finally: This code is always executed.')
+            cleanUp()
+        except Exception as err:
+            print('  -- HELP! Consuming: %s' % type(err))
+
+def c():
+    print('Raising "ExceptionNormal" from c()')
+    raise ExceptionNormal('ExceptionNormal raised from function c()')
+
+def cleanUp():
+    raise ExceptionCleanUp('Can not clean up')
+    
+def main():
+    a()
+    return 0
+
+if __name__ == '__main__':
+    main()